What was the first animal to be domesticated by humans?

The beginnings of animal domestication involved a protracted coevolutionary process with multiple stages along different pathways. It is proposed that there were three major pathways that most animal domesticates followed into domestication: (1) commensals, adapted to a human niche (e.g., dogs, cats, fowl, possibly pigs); (2) prey animals sought for food (e.g., sheep, goats, cattle, water buffalo, yak, pig, reindeer, llama and alpaca); and (3) targeted animals for draft and nonfood resources (e.g., horse, donkey, camel). The dog was the first domesticant, and was established across Eurasia before the end of the Late Pleistocene era, well before cultivation and before the domestication of other animals. Humans did not intend to domesticate animals from, or at least they did not envision a domesticated animal resulting from, either the commensal or prey pathways. In both of these cases, humans became entangled with these species as the relationship between them, and the human role in their survival and reproduction, intensified, leading eventually to a formalised animal husbandry. Although the directed pathway proceeded from capture to taming, the other two pathways are not as goal-oriented and archaeological records suggest that they took place over much longer time frames.

Domestication

Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influence over the reproduction and care of another group to secure a more predictable supply of resources from that second group.

The dog was the first domesticated vertebrate, and was established across Eurasia before the end of the Late Pleistocene era, well before cultivation and before the domestication of other animals. The archaeological and genetic data suggest that long-term bidirectional gene flow between wild and domestic stocks – including donkeys, horses, New and Old World camelids, goats, sheep, and pigs – was common. Given its importance to humans and its value as a model of evolutionary and demographic change, domestication has attracted scientists from archaeology, palaeontology, anthropology, botany, zoology, genetics, and the environmental sciences.
Among birds, the major domestic species today is the chicken, important for meat and eggs, though economically valuable poultry include the turkey, guineafowl and numerous other species. Birds are also widely kept as cagebirds, from songbirds to parrots.
The longest established invertebrate domesticates are the honey bee and the silkworm. Terrestrial snails are raised for food, while species from several phyla are kept for research, and others are bred for biological control.

The domestication of plants began at least 12,000 years ago with cereals in the Middle East, and the bottle gourd in Asia. Agriculture developed in at least 11 different centres around the world, domesticating different crops and animals.

Domestication, from the Latin "", 'belonging to the house', is "a sustained multi-generational, mutualistic relationship in which one organism assumes a significant degree of influence over the reproduction and care of another organism in order to secure a more predictable supply of a resource of interest, and through which the partner organism gains advantage over individuals that remain outside this relationship, thereby benefitting and often increasing the fitness of both the domesticator and the target domesticate." This definition recognizes both the biological and the cultural components of the domestication process and the impacts on both humans and the domesticated animals and plants. All past definitions of domestication have included a relationship between humans with plants and animals, but their differences lay in who was considered as the lead partner in the relationship. This new definition recognizes a mutualistic relationship in which both partners gain benefits. Domestication has vastly enhanced the reproductive output of crop plants, livestock, and pets far beyond that of their wild progenitors. Domesticates have provided humans with resources that they could more predictably and securely control, move, and redistribute, which has been the advantage that had fueled a population explosion of the agro-pastoralists and their spread to all corners of the planet.

Houseplants and ornamentals are plants domesticated primarily for aesthetic enjoyment in and around the home, while those domesticated for large-scale food production are called crops. Domesticated plants deliberately altered or selected for special desirable characteristics are cultigens. Animals domesticated for home companionship are called pets, while those domesticated for food or work are known as livestock.

This biological mutualism is not restricted to humans with domestic crops and livestock but is well-documented in nonhuman species, especially among a number of social insect domesticators and their plant and animal domesticates, for example the ant–fungus mutualism that exists between leafcutter ants and certain fungi.

Domestication syndrome is the suite of phenotypic traits arising during domestication that distinguish crops from their wild ancestors. The term is also applied to vertebrate animals, and includes increased docility and tameness, coat color changes, reductions in tooth size, changes in craniofacial morphology, alterations in ear and tail form (e.g., floppy ears), more frequent and nonseasonal estrus cycles, alterations in adrenocorticotropic hormone levels, changed concentrations of several neurotransmitters, prolongations in juvenile behavior, and reductions in both total brain size and of particular brain regions.

The domestication of animals and plants began with the wolf ("Canis lupus") at least 15,000 years before present (YBP), which then led to a rapid shift in the evolution, ecology, and demography of both humans and numerous species of animals and plants. The sudden appearance of the domestic dog ("Canis lupus familiaris") in the archaeological record was followed by livestock and crop domestication, and the transition of humans from foraging to farming in different places and times across the planet. Around 10,000 YBP, a new way of life emerged for humans through the management and exploitation of plant and animal species, leading to higher-density populations in the centers of domestication, the expansion of agricultural economies, and the development of urban communities.

A 2018 domestication study looked at the reasons why the archeological record that is based on the dating of fossil remains often differed from the genetic record contained within the cells of living species. The study concluded that our inability to date domestication is because domestication is a continuum and there is no single point where we can say that a species was clearly domesticated using these two techniques. The study proposes that changes in morphology across time and how humans were interacting with the species in the past needs to be considered in addition to these two techniques.

The domestication of animals is the mutual relationship between animals with the humans who have influence on their care and reproduction. Charles Darwin recognized the small number of traits that made domestic species different from their wild ancestors. He was also the first to recognize the difference between conscious selective breeding in which humans directly select for desirable traits, and unconscious selection where traits evolve as a by-product of natural selection or from selection on other traits. There is a genetic difference between domestic and wild populations. There is also such a difference between the domestication traits that researchers believe to have been essential at the early stages of domestication, and the improvement traits that have appeared since the split between wild and domestic populations. Domestication traits are generally fixed within all domesticates, and were selected during the initial episode of domestication of that animal or plant, whereas improvement traits are present only in a proportion of domesticates, though they may be fixed in individual breeds or regional populations.

Domestication should not be confused with taming. Taming is the conditioned behavioral modification of an animal to reduce its natural avoidance of humans, and to accept the presence of humans. Domestication is the permanent genetic modification of a bred lineage that leads to an inherited predisposition towards humans. Certain animal species, and certain individuals within those species, make better candidates for domestication than others because they exhibit certain behavioral characteristics: (1) the size and organization of their social structure; (2) the availability and the degree of selectivity in their choice of mates; (3) the ease and speed with which the parents bond with their young, and the maturity and mobility of the young at birth; (4) the degree of flexibility in diet and habitat tolerance; and (5) responses to humans and new environments, including flight responses and reactivity to external stimuli.

Unlike other domestic species which were primarily selected for production-related traits, dogs were initially selected for their behaviors. The archaeological and genetic data suggest that long-term bidirectional gene flow between wild and domestic stocks – including donkeys, horses, New and Old World camelids, goats, sheep, and pigs – was common. One study has concluded that human selection for domestic traits likely counteracted the homogenizing effect of gene flow from wild boars into pigs and created domestication islands in the genome. The same process may also apply to other domesticated animals.

Domesticated birds principally mean poultry, raised for meat and eggs: some Galliformes (chicken, turkey, guineafowl) and Anseriformes (waterfowl: duck, goose, swan). Also widely domesticated are cagebirds such as songbirds and parrots; these are kept both for pleasure and for use in research.
Domestic pigeon is known as a messenger, research suggests it was domesticated as early as 10,000 years ago.
Chickens were domesticated at least 7,000 years ago, with fossils in China from c. 5400 BCE. The chicken's wild ancestor is "Gallus gallus", the red junglefowl of Southeast Asia, and another species, probably the grey junglefowl of India. It appears to have been kept initially for cockfighting rather than for food.

Two insects, the silkworm and the western honey bee, have been domesticated for over 5,000 years, often for commercial use. The silkworm is raised for the silk threads wound around its pupal cocoon; the western honey bee, for honey, and, lately, for pollination of crops.

Several other invertebrates have been domesticated, both terrestrial and aquatic, including some such as "Drosophila melanogaster" fruit flies and the freshwater cnidarian "Hydra" for research into genetics and physiology. Few have a long history of domestication. Most are used for food or other products such as shellac and cochineal. The phyla involved are Cnidaria, Platyhelminthes (for biological control), Annelida, Mollusca, Arthropoda (marine crustaceans as well as insects and spiders), and Echinodermata. While many marine molluscs are used for food, only a few have been domesticated, including squid, cuttlefish and octopus, all used in research on behaviour and neurology. Terrestrial snails in the genera "Helix" and "Murex" are raised for food. Several parasitic or parasitoidal insects including the fly "Eucelatoria", the beetle "Chrysolina", and the wasp "Aphytis" are raised for biological control. Conscious or unconscious artificial selection has many effects on species under domestication; variability can readily be lost by inbreeding, selection against undesired traits, or genetic drift, while in "Drosophila", variability in eclosion time (when adults emerge) has increased.

The initial domestication of animals impacted most on the genes that controlled their behavior, but the initial domestication of plants impacted most on the genes that controlled their morphology (seed size, plant architecture, dispersal mechanisms) and their physiology (timing of germination or ripening).

The domestication of wheat provides an example. Wild wheat shatters and falls to the ground to reseed itself when ripe, but domesticated wheat stays on the stem for easier harvesting. This change was possible because of a random mutation in the wild populations at the beginning of wheat's cultivation. Wheat with this mutation was harvested more frequently and became the seed for the next crop. Therefore, without realizing, early farmers selected for this mutation. The result is domesticated wheat, which relies on farmers for its reproduction and dissemination.

The earliest human attempts at plant domestication occurred in the Middle East. There is early evidence for conscious cultivation and trait selection of plants by pre-Neolithic groups in Syria: grains of rye with domestic traits have been recovered from Epi-Palaeolithic (c. 11,050 BCE) contexts at Abu Hureyra in Syria, but this appears to be a localised phenomenon resulting from cultivation of stands of wild rye, rather than a definitive step towards domestication.

By 10,000 BCE the bottle gourd ("Lagenaria siceraria") plant, used as a container before the advent of ceramic technology, appears to have been domesticated. The domesticated bottle gourd reached the Americas from Asia by 8000 BCE, most likely due to the migration of peoples from Asia to America.

Cereal crops were first domesticated around 9000 BCE in the Fertile Crescent in the Middle East. The first domesticated crops were generally annuals with large seeds or fruits. These included pulses such as peas and grains such as wheat. The Middle East was especially suited to these species; the dry-summer climate was conducive to the evolution of large-seeded annual plants, and the variety of elevations led to a great variety of species. As domestication took place humans began to move from a hunter-gatherer society to a settled agricultural society. This change would eventually lead, some 4000 to 5000 years later, to the first city states and eventually the rise of civilization itself.

Continued domestication was gradual, a process of intermittent trial and error. Over time perennials and small trees including the apple and the olive were domesticated. Some plants, such as the macadamia nut and the pecan, were not domesticated until recently.

In other parts of the world very different species were domesticated. In the Americas squash, maize, beans, and perhaps manioc (also known as cassava) formed the core of the diet. In East Asia millet, rice, and soy were the most important crops. Some areas of the world such as Southern Africa, Australia, California and southern South America never saw local species domesticated.

Domesticated plants may differ from their wild relatives in many ways, including

There are many challenges facing modern farmers, including climate change, pests, soil salinity, drought, and periods with limited sunlight.

Drought is one of the most serious challenges facing farmers today. With shifting climates comes shifting weather patterns, meaning that regions that could traditionally rely on a substantial amount of precipitation were, quite literally, left out to dry. In light of these conditions, drought resistance in major crop plants has become a clear priority. One method is to identify the genetic basis of drought resistance in naturally drought resistant plants, i.e. the Bambara groundnut. Next, transferring these advantages to otherwise vulnerable crop plants. Rice, which is one of the most vulnerable crops in terms of drought, has been successfully improved by the addition of the Barley hva1 gene into the genome using transgenetics. Drought resistance can also be improved through changes in a plant's root system architecture, such as a root orientation that maximizes water retention and nutrient uptake. There must be a continued focus on the efficient usage of available water on a planet that is expected to have a population in excess of nine-billion people by 2050.

Another specific area of genetic improvement for domesticated crops is the crop plant's uptake and utilization of soil potassium, an essential element for crop plants yield and overall quality. A plant's ability to effectively uptake potassium and utilize it efficiently is known as its potassium utilization efficiency. It has been suggested that first optimizing plant root architecture and then root potassium uptake activity may effectively improve plant potassium utilization efficiency.

Cereals, rice, wheat, corn, and barley, make up a huge amount of the global diet across all demographic and social scales. These cereal crop plants are all autogamous, i.e. self- fertilizing, which limits overall diversity in allelic combinations, and therefore adaptability to novel environments. To combat this issue the researchers suggest an "Island Model of Genomic Selection". By breaking a single large population of cereal crop plants into several smaller sub-populations which can receive "migrants" from the other subpopulations, new genetic combinations can be generated.

The Bambara groundnut is a durable crop plant that, like many underutilized crops, has received little attention in an agricultural sense. The Bambara Groundnut is drought resistant and is known to be able to grow in almost any soil conditions, no matter how impoverished an area may be. New genomic and transcriptomic approaches are allowing researchers to improve this relatively small-scale crop, as well as other large-scale crop plants. The reduction in cost, and wide availability of both microarray technology and Next Generation Sequencing have made it possible to analyze underutilized crops, like the groundnut, at genome-wide level. Not overlooking particular crops that don't appear to hold any value outside of the developing world will be key to not only overall crop improvement, but also to reducing the global dependency on only a few crop plants, which holds many intrinsic dangers to the global population's food supply.

The semi-arid tropics, ranging from parts of North and South Africa,Asia especially in the South Pacific, all the way to Australia are notorious for being both economically destitute and agriculturally difficult to cultivate and farm effectively. Barriers include everything from lack of rainfall and diseases, to economic isolation and environmental irresponsibility. There is a large interest in the continued efforts, of the International Crops Research Institute for the Semi-Arid Tropics (ICRSAT) to improve staple foods. some mandated crops of ICRISAT include the groundnut, pigeonpea, chickpea, sorghum and pearl millet, which are the main staple foods for nearly one billion people in the semi-arid tropics. As part of the ICRISAT efforts, some wild plant breeds are being used to transfer genes to cultivated crops by interspecific hybridization involving modern methods of embryo rescue and tissue culture. One example of early success has been work to combat the very detrimental peanut clump virus. Transgenetic plants containing the coat protein gene for resistance against peanut clump virus have already been produced successfully. Another region threatened by food security are the Pacific Island Countries, which are disproportionally faced with the negative effects of climate change. The Pacific Islands are largely made up of a chain of small bodies of land, which obviously limits the amount of geographical area in which to farm. This leaves the region with only two viable options 1.) increase agricultural production or 2.) increase food importation. The latter of course runs into the issues of availability and economic feasibility, leaving only the first option as a viable means to solve the region's food crisis. It is much easier to misuse the limited resources remaining, as compared with solving the problem at its' core.

Work has also has been focusing on improving domestic crops through the use of crop wild relatives. The amount and depth of genetic material available in crop wild relatives is larger than originally believed, and the range of plants involved, both wild and domestic, is ever expanding. Through the use of new biotechnological tools such as genome editing, cisgenesis/intragenesis, the transfer of genes between crossable donor species including hybrids, and other omic approaches.

Wild plants can be hybridized with crop plants to form perennial crops from annuals, increase yield, growth rate, and resistance to outside pressures like disease and drought. It is important to remember that these changes take significant lengths of time to achieve, sometimes even decades. However, the outcome can be extremly successful as is the case with a hybrid grass variant known as "Kernza." Over the course of nearly three decades, work was done on an attempted hybridization between an already domesticated grass strain, and several of its wild relatives. The domesticated strain as was more uniform in its orientation, but the wild strains were larger and propagated faster. The resulting "Kernza" crop has traits from both progenitors: uniform orientation and a linearly vertical root system from the domesticated crop, along with increased size and rate of propagation from the wild relatives.

Several species of fungi have been domesticated for use directly as food, or in fermentation to produce foods and drugs. The white button mushroom "Agaricus bisporus" is widely grown for food. The yeast "Saccharomyces cerevisiae" have been used for thousands of years to ferment beer and wine, and to leaven bread. Mould fungi including "Penicillium" are used to mature cheeses and other dairy products, as well as to make drugs such as antibiotics.

Selection of animals for visible "desirable" traits may have undesired consequences. Captive and domesticated animals often have smaller size, piebald color, shorter faces with smaller and fewer teeth, diminished horns, weak muscle ridges, and less genetic variability. Poor joint definition, late fusion of the limb bone epiphyses with the diaphyses, hair changes, greater fat accumulation, smaller brains, simplified behavior patterns, extended immaturity, and more pathology are among the defects of domestic animals. All of these changes have been documented by archaeological evidence, and confirmed by animal breeders in the 20th century. In 2014, a study proposed the theory that under selection, docility in mammals and birds results partly from a slowed pace of neural crest development, that would in turn cause a reduced fear–startle response due to mild neurocristopathy that causes domestication syndrome. The theory was unable to explain curly tails nor domestication syndrome exhibited by plants.

A side effect of domestication has been zoonotic diseases. For example, cattle have given humanity various viral poxes, measles, and tuberculosis; pigs and ducks have given influenza; and horses have given the rhinoviruses. Many parasites have their origins in domestic animals. The advent of domestication resulted in denser human populations which provided ripe conditions for pathogens to reproduce, mutate, spread, and eventually find a new host in humans.

Paul Shepard writes "Man substitutes controlled breeding for natural selection; animals are selected for special traits like milk production or passivity, at the expense of overall fitness and nature-wide relationships...Though domestication broadens the diversity of forms – that is, increases visible polymorphism – it undermines the crisp demarcations that separate wild species and cripples our recognition of the species as a group. Knowing only domestic animals dulls our understanding of the way in which unity and discontinuity occur as patterns in nature, and substitutes an attention to individuals and breeds. The wide variety of size, color, shape, and form of domestic horses, for example, blurs the distinction among different species of "Equus" that once were constant and meaningful."

Jared Diamond in his book "Guns, Germs, and Steel" describes the universal tendency for populations that have acquired agriculture and domestic animals to develop a large population and to expand into new territories. He recounts migrations of people armed with domestic crops overtaking, displacing or killing indigenous hunter-gatherers, whose lifestyle is coming to an end.

Some anarcho-primitivist authors describe domestication as the process by which previously nomadic human populations shifted towards a sedentary or settled existence through agriculture and animal husbandry. They claim that this kind of domestication demands a totalitarian relationship with both the land and the plants and animals being domesticated. They say that whereas, in a state of wildness, all life shares and competes for resources, domestication destroys this balance. Domesticated landscape (e.g. pastoral lands/agricultural fields and, to a lesser degree, horticulture and gardening) ends the open sharing of resources; where "this was everyone's", it is now "mine". Anarcho-primitivists state that this notion of ownership laid the foundation for social hierarchy as property and power emerged. It also involved the destruction, enslavement, or assimilation of other groups of early people who did not make such a transition.

In 2016, a study found that humans have had a major impact on global genetic diversity as well as extinction rates, including a contribution to megafaunal extinctions. Pristine landscapes no longer exist and have not existed for millennia, and humans have concentrated the planet's biomass into human-favored plants and animals. Domesticated ecosystems provide food, reduce predator and natural dangers, and promote commerce, but have also resulted in habitat loss and extinctions commencing in the Late Pleistocene. Ecologists and other researchers are advised to make better use of the archaeological and paleoecological data available for gaining an understanding the history of human impacts before proposing solutions.

The dog was the first domesticated animal, and was domesticated and widely established across Eurasia before the end of the Pleistocene, well before the cultivation of crops or the domestication of other animals. The dog is often hypothesised to be a classic example of a domestic animal that likely traveled a commensal pathway into domestication. Archaeological evidence, such as the Bonn-Oberkassel dog dating to ~14,000BP, supports the hypothesis that dog domestication preceded the emergence of agriculture and began close to the Last Glacial Maximum when hunter-gatherers preyed on megafauna.
The wolves more likely drawn to human camps were the less-aggressive, subdominant pack members with lowered flight response, higher stress thresholds, and less wary around humans, and therefore better candidates for domestication.
Proto-dogs might have taken advantage of carcasses left on site by early hunters, assisted in the capture of prey, or provided defense from large competing predators at kills. However, the extent to which proto-domestic wolves could have become dependent on this way of life prior to domestication and without human provisioning is unclear and highly debated. In contrast, cats may have become fully dependent on a commensal lifestyle before being domesticated by preying on other commensal animals, such as rats and mice, without any human provisioning. Debate over the extent to which some wolves were commensal with humans prior to domestication stems from debate over the level of human intentionality in the domestication process, which remains untested.

Commensalism

Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit from each other, amensalism, where one is harmed while the other is unaffected, and parasitism, where one benefits while the other is harmed. The commensal (the species that benefits from the association) may obtain nutrients, shelter, support, or locomotion from the host species, which is substantially unaffected. The commensal relation is often between a larger host and a smaller commensal; the host organism is unmodified, whereas the commensal species may show great structural adaptation consonant with its habits, as in the remoras that ride attached to sharks and other fishes. Both remora and pilot fish feed on the leftovers of their hosts' meals. Numerous birds perch on bodies of large mammal herbivores or feed on the insects turned up by grazing mammals.

The word "commensalism" is derived from the word "commensal", meaning "eating at the same table" in human social interaction, which in turn comes through French from the Medieval Latin "commensalis", meaning "sharing a table", from the prefix "com-", meaning "together", and "mensa", meaning "table" or "meal". Commensality, at Oxford and Cambridge Universities, refers to professors eating at the same table as students (as they live in the same "college").

Pierre-Joseph van Beneden introduced the term "commensalism" in 1876.

The commensal pathway was traveled by animals that fed on refuse around human habitats or by animals that preyed on other animals drawn to human camps. Those animals established a commensal relationship with humans in which the animals benefited but the humans received little benefit or harm. Those animals that were most capable of taking advantage of the resources associated with human camps would have been the ‘tamer’ individuals: less aggressive, with shorter fight or flight distances. Later, these animals developed closer social or economic bonds with humans and lead to a domestic relationship.

The leap from a synanthropic population to a domestic one could only have taken place after the animals had progressed from anthropophily to habituation, to commensalism and partnership, at which point the establishment of a reciprocal relationship between animal and human would have laid the foundation for domestication, including captivity and human-controlled breeding. From this perspective, animal domestication is a coevolutionary process in which a population responds to selective pressure while adapting to a novel niche that includes another species with evolving behaviors.

Commensal pathway animals include dogs, cats, fowl, and possibly pigs.

The earliest sign of domestication in dogs was the neotonization of skull morphology and the shortening of snout length that results in tooth crowding, reduction in tooth size, and a reduction in the number of teeth, which has been attributed to the strong selection for reduced aggression. This process may have begun during the initial commensal stage of dog domestication, even before humans began to be active partners in the process.

A mitochondrial, microsatellite, and Y-chromosome assessment of two wolf populations in North America combined with satellite telemetry data revealed significant genetic and morphological differences between one population that migrated with and preyed upon caribou and another territorial ecotype population that remained in a boreal coniferous forest. Although these two populations spend a period of the year in the same place, and though there was evidence of gene flow between them, the difference in prey–habitat specialization has been sufficient to maintain genetic and even coloration divergence.

A different study has identified the remains of a population of extinct Pleistocene Beringian wolves with unique mitochondrial signatures. The skull shape, tooth wear, and isotopic signatures suggested these remains were derived from a population of specialist megafauna hunters and scavengers that became extinct while less specialized wolf ecotypes survived. Analogous to the modern wolf ecotype that has evolved to track and prey upon caribou, a Pleistocene wolf population could have begun following mobile hunter-gatherers, thus slowly acquiring genetic and phenotypic differences that would have allowed them to more successfully adapt to the human habitat.

Numerous genera of bacteria and fungi live on and in the human body as part of its natural flora. The fungal genus "Aspergillus" is capable of living under considerable environmental stress, and thus is capable of colonising the upper gastrointestinal tract where relatively few examples of the body's gut flora can survive due to highly acidic or alkaline conditions produced by gastric acid and digestive juices. While "Aspergillus" normally produces no symptoms, in individuals who are immunocompromised or suffering from existing conditions such as tuberculosis, a condition called aspergillosis can occur, in which populations of "Aspergillus" grow out of control.

"Staphylococcus aureus", a common bacterial species, is known best for its numerous pathogenic strains that can cause numerous illnesses and conditions. However, many strains of "S. aureus" are metabiotic commensals, and are present on roughly 20 to 30% of the human population as part of the skin flora. "S. aureus" also benefits from the variable ambient conditions created by the body's mucous membranes, and as such can be found in the oral and nasal cavities, as well as inside the ear canal. Other "Staphylococcus" species including "S. warneri", "S. lugdunensis" and "S. epidermidis", will also engage in commensalism for similar purposes.

Whether the relationship between humans and some types of gut flora is commensal or mutualistic is still unanswered.

Some biologists argue that any close interaction between two organisms is unlikely to be completely neutral for either party, and that relationships identified as commensal are likely mutualistic or parasitic in a subtle way that has not been detected. For example, epiphytes are "nutritional pirates" that may intercept substantial amounts of nutrients that would otherwise go to the host plant. Large numbers of epiphytes can also cause tree limbs to break or shade the host plant and reduce its rate of photosynthesis. Similarly, phoretic mites may hinder their host by making flight more difficult, which may affect its aerial hunting ability or cause it to expend extra energy while carrying these passengers.

Like all ecological interactions, commensalisms vary in strength and duration from intimate, long-lived symbioses to brief, weak interactions through intermediaries.

Phoresy is one animal attached to another exclusively for transport, mainly arthropods, examples of which are mites on insects (such as beetles, flies or bees), pseudoscorpions on mammals or beetles, and millipedes on birds. Phoresy can be either obligate or facultative (induced by environmental conditions).

Inquilinism is the use of a second organism for permanent housing. Examples are epiphytic plants (such as many orchids) that grow on trees, or birds that live in holes in trees.

Metabiosis is a more indirect dependency, in which one organism creates or prepares a suitable environment for a second. Examples include maggots, which feast and develop on corpses, and hermit crabs, which use gastropod shells to protect their bodies.

The dog is a classic example of a domestic animal that likely traveled a commensal pathway into domestication. The dog was the first domesticant, and was domesticated and widely established across Eurasia before the end of the Pleistocene, well before cultivation or the domestication of other animals. It may have been inevitable that the first domesticated animal came from the order of carnivores as these are less afraid when approaching other species. Within the carnivores, the first domesticated animal would need to exist without an all-meat diet, possess a running and hunting ability to provide its own food, and be of a controllable size to coexist with humans, indicating the family "Canidae", and the right temperament with wolves being among the most gregarious and cooperative animals on the planet.

Origin of the domestic dog

The origin of the domestic dog is not clear. The domestic dog is a member of the genus "Canis", which forms part of the wolf-like canids, and is the most widely abundant terrestrial carnivore. The closest living relative of the dog is the extant gray wolf, and there is no evidence of any other canine contributing to its genetic lineage. The dog and the extant gray wolf are sister taxa, as modern wolves are not closely related to the wolves that were first domesticated. The archaeological record and genetic analysis show the remains of the Bonn–Oberkassel dog buried beside humans 14,200 years ago to be the first undisputed dog, with disputed remains occurring 36,000 years ago. These dates imply that the earliest dogs arose in the time of human hunter-gatherers and not agriculturists. The dog was the first species to be domesticated.

Where the genetic divergence of dog and wolf took place remains controversial, with the most plausible proposals spanning Western Europe, Central Asia and East Asia. This has been made more complicated by the most recent proposal that fits the available evidence, which is that an initial wolf population split into East and West Eurasian groups; these, before going extinct, were domesticated independently into two distinct dog populations between 14,000 and 6,400 years ago. The Western Eurasian dog population was partially and gradually replaced by East Asian dogs introduced by humans at least 6,400 years ago.

Six million years ago, towards the close of the Miocene era, the earth's climate was gradually cooling and this led to the glaciations of the Pliocene and the Pleistocene – the Ice Age. In many areas, forests and savannahs were replaced with steppe or grasslands and only those creatures that could adapt survived.

In southern North America, small woodland foxes grew bigger and better adapted to running, and by the late Miocene the first of the genus "Canis" had arisen - the ancestors of coyotes, wolves and the domestic dog. In eastern Africa, a split occurred among the large primates. Some remained in the trees, while others came down from the trees, learned to walk upright, developed larger brains, and in the more open country learned to avoid predators while becoming predators themselves. The ancestors of humans and dogs ultimately met in Eurasia.

Human hunter-gathers did not live in fear of nature and knew that they posed a formidable risk to any potential predators. The Ju'wasi people of Namibia share their land with prides of lions. Both species coexist with respect and without fear or hostility in a relationship that may go back to the dawn of modern humans. The lion is a larger and far more dangerous predator than the wolf. Early modern humans entering Eurasia and first encountering packs of wolves may have been assisted in living among them because of the traditional beliefs of their African ancestors. In historical times, mutual respect and cooperation with canids can be found in the stories and traditions of the indigenous peoples of Siberia, East Asia, North America, and Australia.

The causes and context of dog domestication are not known. Deriving a time and a place for domestication could help describe the conditions that gave rise to an association of a large carnivore with hunter-gatherers. All other domestication events occurred during or after the development of agriculture, which was approximately 10,000 years before present (YBP). The earlier association of dogs with humans may have allowed dogs to have a profound influence on the course of early human history and the development of civilization. However, the timing, geographic locations, and ecological conditions that led to dog domestication are not agreed.

When and where dogs were first domesticated has taxed geneticists for the past 20 years and archaeologists for many decades longer. Identifying the earliest dogs is difficult because the key morphological characters that are used by zooarchaeologists to differentiate domestic dogs from their wild wolf ancestors (size and position of teeth, dental pathologies, and size and proportion of cranial and postcranial elements) were not yet fixed during the initial phases of the domestication process. The range of natural variation among these characters that may have existed in ancient wolf populations, and the time it took for these traits to appear in dogs, are unknown.

Among archeologists, the proposed timing of the development of a relationship between humans and wolves is debated. There exists two schools of thought. The early domestication theory argues that the relationship commenced once humans moved into the colder parts of Eurasia around 35,000 YBP, which is when the proposed Paleolithic dogs first began to appear. Wolves that were adjusting to live with humans may have developed shorter, wider skulls and more steeply-rising foreheads that would make wolf facial expressions easier to interpret. The late domestication theory argues that Paleolithic dogs are an unusual phenotype of wolf and that dogs appeared only when they could be phenotypically distinguishable from the wolf, which is usually based on a reduction in size. This argument maintains that domesticated dogs are more clearly identified when they are associated with human occupation, and those interred side-by-side with human remains provide the most conclusive evidence, commencing with the 14,200 years old Bonn-Oberkassel dog.

The debate centres around "Homo sapiens" and if they had entered into cooperation with wolves soon after they moved into Eurasia, and if so when and where did these wolves change into domesticated dogs. In arguing that domestication leads to reduction in size, the late domestication theory ignores that modern horses and pigs are larger than their wild ancestors. It also ignores that if hunter-gathers entered into a hunting relationship with wolves then there would be no need of selection for a reduction in size. A reduction in size would have occurred much later when humans moved into agricultural villages. The late domestication theory does not consider the possibility that humans may have formed a relationship with non-domesticated wolves and that dogs in the early stages of domestication might be indistinguishable from wolves. According to indigenous North Americans, over the past 20,000 years the canids living with them were wolves that could not be distinguished as dogs.

The problem in attempting to identify when and where domestication occurred is the possibility that the process of domestication occurred in a number of places and at a number of times throughout prehistory. Early dog remains have been found in different parts of the world. This suggests that dog domestication may have taken place in different regions independently by hunter-gatherers, in some cases at the same time and in other cases at different times, with different wolf subspecies producing different dog lineages. Therefore, the number of dog domestication events is not known. A study of the maternal mitochondrial DNA (mDNA) shows that dogs fall within 4 mDNA clades, indicating that dogs are derived from 4 separate lineages and therefore there may not have been a single domestication event.

A domestication study looked at the reasons why the archeological record that is based on the dating of fossil remains often differed from the genetic record contained within the cells of living species. The study concluded that our inability to date domestication is because domestication is a continuum and there is no single point where we can say that a species was clearly domesticated using these two techniques. The study proposes that changes in morphology across time and how humans were interacting with the species in the past needs to be considered in addition to these two techniques.

The table below lists by location and timing in years before present the very early co-location of hominid and wolf specimens, then some proposed Paleolithic dogs, followed by the first undisputed dog remains.

Genetic studies indicate that the gray wolf is the closest living relative of the dog, with no evidence of any other canine species having contributed. Attempting to reconstruct the dog's lineage through the phylogenetic analysis of DNA sequences from modern dogs and wolves has given conflicting results for several reasons. Firstly, studies indicate that an extinct Late Pleistocene wolf is the nearest common ancestor to the dog, with modern wolves not being the dog's direct ancestor. Secondly, the genetic divergence between the dog and modern wolves occurred over a short period of time, so that the time of the divergence is difficult to date (referred to as incomplete lineage sorting). This is complicated further by the cross-breeding that has occurred between dogs and wolves since domestication (referred to as post-domestication gene flow). Finally, there have been only tens of thousands of generations of dogs since domestication, so that the number of mutations between the dog and the wolf are few and this makes the timing of domestication difficult to date.

However, recent studies based on genetics propose five generalizations about dogs.The extinction of the wolves that were the direct ancestors of dogs, and the sustained admixture between different dog and wolf populations over at least the last 10,000 years, has blurred the genetic signatures and confounded efforts of researchers at pinpointing the origins of dogs. An alternate proposal is that during the ecological upheavals of the Late Pleistocene, all of the remaining members of a dwindling lineage joined with humans.

The archaeological and paleontological records show gray wolf continuous presence for at least the last 300,000 years. This continuous presence contrasts with genomic analyses. Two studies of the mitochondrial genome of both modern and extinct grey wolves ("Canis lupus") have been conducted. The ancient specimens were radiocarbon dated and stratagraphically dated, and together with DNA sequences a time-based phylogenetic tree was generated for wolves. The study inferred that the most recent common ancestor for all "Canis lupus" specimens – modern and extinct – was 80,000 years before present. Other studies suggest that all modern wolves and dogs descend from a common ancestral wolf population that existed as recently as 20,000 years ago. These analyses indicate a population bottleneck, followed by a rapid radiation from an ancestral population at a time during, or just after, the Last Glacial Maximum. However, the geographic origin of this radiation is not known.

During the last Ice Age, the most recent peak is known as the Last Glacial Maximum when a vast mammoth steppe stretched from Spain eastwards across Eurasia and over the Bering land bridge into Alaska and the Yukon. The continent of Europe was much colder and drier than it is today, with polar desert in the north and the remainder steppe or tundra. Forest and woodland were almost non-existent except for isolated pockets in the mountain ranges of southern Europe. The Late Pleistocene was characterized by a series of severe and rapid climate oscillations with regional temperature changes of up to 16 °C, which has been correlated with Pleistocene megafaunal extinctions. There is no evidence of megafaunal extinctions at the height of the Last Glacial Maximum, indicating that increasing cold and glaciation were not factors. Multiple events appear to have caused the rapid replacement of one species by another one within the same genus, or one population by another within the same species, across a broad area. As some species became extinct, so too did the predators that depended on them. The ancestors of modern humans first reached Europe between 43,000-45,000 years BP, with their remains found in Italy and in Britain.

During the Last Glacial Maximum there were two types of wolf. The cold north of the Holarctic was spanned by a large, robust, wolf ecomorph that specialised in preying on megafauna. Another more slender form lived in refuges from the glaciation. When the planet warmed and the Late Glacial Maximum came to a close, whole species of megafauna became extinct along with their predators, leaving the more gracile wolf to dominate the Holarctic. The more gracile wolf was the ancestor of the modern gray wolf, which is the dog's sister but not its ancestor as the dog shows a closer genetic relationship to the now-extinct megafaunal wolf."

The date estimated for the evolutionary divergence of a domestic lineage from a wild one does not necessarily indicate the start of the domestication process but it does provide an upper boundary. The divergence of the domestic horse from the lineage that led to the modern Przewalski's horse is estimated to have occurred around 45,000 YBP but the archaeological record indicates 5,500 YBP. The variance could be due to the modern wild population not being the direct ancestor of the domestic one, or the impact of a split due to climate, topography, or other environmental changes. The divergence time does not imply domestication during this specific period. Some researchers propose that the "dog was the dog before it was domesticated" and that the ancestor of "Canis familiaris" was a wild "Canis familiaris", which had diverged from a common ancestor along with the modern grey wolf.

An early mitochondrial DNA analysis of modern dogs and wolves indicated that if the dog had descended from the modern grey wolf then the divergence occurred 100,000–135,000 YBP. Two later studies using whole genome sequencing of modern dogs and wolves indicated divergence times of 32,000 YBP or 11,000-16,000 YBP. A later study of the whole genomes of modern dogs and wolves, and the genome extracted from a 34,900 YBP fossil of a Taimyr wolf indicates that the Taimyr wolf population, gray wolves, and dogs diverged from a now-extinct common ancestor before the peak of the Last Glacial Maximum 27,000-40,000 years ago. In 2017, a study compared the nuclear genome sequences of 3 fossil Neolithic dog specimens with sequences from modern dogs and wolves, giving a divergence time of 36,900-41,500 YBP. In 2018, a study looked at the y-chromosome male lineage of canines including the 3 Neolithic dog specimens, which indicates that the dog male lineage diverged from its nearest common ancestor shared with the gray wolf between 68,000-151,000 YBP.

Towards the end of 2018, a study resequenced and compared the genomes of 48 modern wolf-like canids. The study found that the dog and the modern grey wolf diverged 31,000 YBP. Additionally, the study also indicates that the common ancestor of the coyote and gray wolf lineage has genetically admixed with a ghost population of an extinct unidentified canid. The canid is genetically close to the dhole and has evolved after the divergence of the African hunting dog from the other canid species.

The grey wolf "Canis lupus" is a highly adaptable species that is able to exist in a range of environments and which possesses a wide distribution across Eurasia and North America. Studies of modern grey wolves have identified distinct sub-populations that live in close proximity to each other. This variation in sub-populations is closely linked to differences in habitat - precipitation, temperature, vegetation, and prey specialization - which affect cranio-dental plasticity. The archaeological and paleontological records show their continuous presence for at least the last 300,000 years. This continuous presence contrasts with genomic analyses, which suggest that all modern wolves and dogs descend from a common ancestral wolf population that existed as recently as 20,000 years ago. These analyses indicate a population bottleneck, followed by a rapid radiation from an ancestral population at a time during, or just after, the Last Glacial Maximum. However, the geographic origin of this radiation is not known.

Where the genetic divergence of dog and wolf took place remains controversial, with the most plausible proposals spanning Western Europe, Central Asia, and East Asia. This has been made more complicated by the most recent proposal that fits the available evidence, which is that an initial wolf population split into East and West Eurasian wolves, these were then domesticated independently before going extinct into two distinct dog populations between 14,000-6,400 years ago, and then the Western Eurasian dog population was partially and gradually replaced by East Asian dogs that were brought by humans at least 6,400 years ago.

Europe
In 2007, a study of maternal mDNA sequences from dogs and wolves indicated that their haplotypes resolved into four monophyletic clades (a grouping that includes its ancestor), of which two clades showed a strong relationship between dogs and the wolves of Europe.

South East Asia:
In 2009, a study of the maternal mitochondrial genome indicated the origin in south-eastern Asia south of the Yangtze River as more dog haplogroups had been found there. Paternal Y-chromosome DNA sequences indicated the south-western part of south-eastern Asia that is south of the Yangtze River (comprising South-East Asia and the Chinese provinces of Yunnan and Guangxi) because of the greater diversity of yDNA haplogroups found in that region. A criticism of this proposal is that no wolf remains have been found in this region and the earliest archaeological evidence of a dog dates to only 4,700 YBP.

Middle East: In 2010, a study using single nucleotide polymorphisms indicated that dogs originated in the Middle East due to the greater sharing of haplotypes between dogs and Middle Eastern gray wolves, else there may have been significant admixture between some regional breeds and regional wolves. In 2011, a study found that there had been dog-wolf hybridization and not an independent domestication.

East Asia: In 2002, a study of maternal mDNA indicated that the dog diverged from its ancestor in East Asia because there were more dog mDNA haplotypes found there than in other parts of the world, but this was rebutted because village dogs in Africa also show a similar haplotype diversity. In 2015, a whole genome analysis of modern dog and wolf sequences concluded that based on the genetic diversity of today's East Asian dogs, the dog had originated in southern East Asia, followed by a migration of a subset of ancestral dogs 15,000 YBP towards the Middle East, Africa and Europe and reaching Europe 10,000 YBP. Then, one of these lineages migrated back to northern China and admixed with endemic Asian lineages before migrating to the Americas. A criticism of this proposal is that no dog remains date beyond 12,000 YBP in this region but date to 14,000 YBP in western Europe, however it is accepted that archaeological studies in the Far East are generally lagging behind those in Europe.

Central Asia: In 2015, a study looked at 85,805 genetic markers of autosomal, maternal mitochondrial genome and paternal Y chromosome diversity in 4,676 purebred dogs from 161 breeds and 549 village dogs from 38 countries. Some dog populations in the Neotropics and the South Pacific are almost completely derived from European stock, and other regions show clear admixture between indigenous and European dogs. The indigenous dog populations of Vietnam, India, and Egypt show minimal evidence of European admixture, and exhibit indicators consistent with a Central Asian domestication origin, followed by a population expansion in East Asia. The study could not rule out the possibility that dogs were domesticated elsewhere and subsequently arrived in and diversified from Central Asia. Studies of extant dogs cannot exclude the possibility of earlier domestication events that subsequently died out or were overwhelmed by more modern populations.

No agreement using modern DNA: In 2016, a whole-genome study of wolves and dogs concluded that admixture had confounded the ability to make inferences about the place of dog domestication. Past studies based on single-nucleotide polymorphisms, genome-wide similarities with Chinese wolves, and lower linkage disequilibrium might reflect regional admixture between dogs with wolves and gene flow between dog populations, with genetically divergent dog breeds possibly maintaining more wolf ancestry in their genome. The study proposed that the analysis of ancient DNA might be a better approach.

In his 1868 book on "Variation under Domestication", Charles Darwin assessed the arguments for single or multiple origins of dogs, and noted the paleontological research of de Blainville who proposed that dogs were descended from a single extinct species. In 1934, an eminent paleontologist indicated that the ancestor of the dog lineage may have been the extinct "Canis variabilis". In 1950, a morphological study of Japanese prehistoric dogs compared to extant wolves concluded: "Therefore the living wolf kinds have nothing to do with the ancestral forms of the prehistoric dog races." In 1999, a study emphasized that while molecular genetic data seem to support the origin of dogs from wolves, dogs may have descended from a now extinct species of canid whose closest living relative was the wolf. The dog's lineage may have been contributed to from a ghost population. The advent of rapid and inexpensive DNA sequencing technology has made it possible to significantly increase the resolving power of genetic data taken from both modern and ancient domestic dog genomes. Attention was now turned to studies based on ancient DNA from fossil canids.

Europe: In 2013, a study analysed the complete and partial mitochondrial genome sequences of 18 fossil canids dated from 1,000 to 36,000 YBP from the Old and New Worlds, and compared these with the complete mitochondrial genome sequences from modern wolves and dogs. Phylogenetic analysis showed that modern dog mDNA haplotypes resolve into four monophyletic clades with strong statistical support, and these have been designated by researchers as clades A-D. Based on the specimens used in this study, clade A included 64% of the dogs sampled and these were sister to a 14,500 YBP wolf sequence from the near Thayngen in the canton of Schaffhausen, Switzerland, with a most recent common ancestor estimated to 32,100 YBP. This group of dogs matched three fossil pre-Columbian New World dogs dated between 1,000 and 8,500 YBP, which supported the hypothesis that pre-Columbian dogs in the New World share ancestry with modern dogs and that they likely arrived with the first humans to the New World. Clade B included 22% of the dog sequences and was related to modern wolves from Sweden and the Ukraine, with a common recent ancestor estimated to 9,200 YBP. However, this relationship might represent mitochondrial genome introgression from wolves because dogs were domesticated by this time. Clade C included 12% of the dogs sampled and these were sister to two ancient dogs from the Bonn-Oberkassel cave (14,700 YBP) and the Kartstein cave (12,500 YBP) near Mechernich in Germany, with a common recent ancestor estimated to 16,000–24,000 YBP. Clade D contained sequences from 2 Scandinavian breeds (Jamthund, Norwegian Elkhound) and were sister to another 14,500 YBP wolf sequence also from the Kesserloch cave, with a common recent ancestor estimated to 18,300 YBP. Its branch is phylogenetically rooted in the same sequence as the "Altai dog" (not a direct ancestor). The data from this study indicated a European origin for dogs that was estimated at 18,800–32,100 years ago based on the genetic relationship of 78% of the sampled dogs with ancient canid specimens found in Europe. The data supports the hypothesis that dog domestication preceded the emergence of agriculture and was initiated close to the Last Glacial Maximum when hunter-gatherers preyed on megafauna.

The study found that three ancient Belgium canids (the 36,000 YBP "Goyet dog" cataloged as "Canis" species, along with Belgium 30,000 YBP and 26,000 years YBP cataloged as "Canis lupus") formed an ancient clade that was the most divergent group. The study found that the skulls of the "Goyet dog" and the "Altai dog" had some dog-like characteristics and proposed that the may have represented an aborted domestication episode. If so, there may have been originally more than one ancient domestication event for dogs as there was for domestic pigs.

One theory is that domestication occurred during one of the five cold Heinrich events that occurred after the arrival of humans in West Europe 37 000, 29 000, 23 000, 16 500 and 12 000 YBP. The theory is that the extreme cold during one of these events caused humans to either shift their location, adapt through a breakdown in their culture and change of their beliefs, or adopt innovative approaches. The adoption of the large wolf/dog was an adaptation to this hostile environment.

A criticism of the European proposal is that dogs in East Asia show more genetic diversity. However, dramatic differences in genetic diversity can be influenced both by an ancient and recent history of inbreeding. A counter-comment is that the modern European breeds only emerged in the 19th century, and that throughout history global dog populations experienced numerous episodes of diversification and homogenization, with each round further reducing the power of genetic data derived from modern breeds to help infer their early history.

Arctic North-East Siberia: In 2015, a study looked at the mitochondrial control region sequences of 13 ancient canid remains and one modern wolf from five sites across Arctic north-east Siberia. The fourteen canids revealed nine mitochondrial haplotypes, three of which were on record and the others not reported before. The phylogentic tree generated from the sequences showed that four of the Siberian canids dated 28,000 YBP and one "Canis c.f. variabilis" dated 360,000 YBP were highly divergent. The haplotype designated as S805 (28,000 YBP) from the Yana River was one mutation away from another haplotype S902 (8,000 YBP) that represents Clade A of the modern wolf and domestic dog lineages. Closely related to this haplotype was one that was found in the recently-extinct Japanese wolf. Several ancient haplotypes were oriented around S805, including "Canis c.f. variabilis" (360,000 YBP), Belgium (36,000 YBP – the "Goyet dog"), Belgium (30,000 YBP), and Konsteki, Russia (22,000 YBP). Given the position of the S805 haplotype on the phylogenetic tree, it may potentially represent a direct link from the progenitor (including "Canis c.f. variabilis") to the domestic dog and modern wolf lineages. The gray wolf is thought to be ancestral to the domestic dog, however its relationship to "C. variabilis", and the genetic contribution of "C. variabilis" to the dog, is the subject of debate.

The Zhokhov Island (8,700 YBP) and Aachim (1,700 YBP) canid haplotypes fell within the domestic dog clade, cluster with S805, and also share their haplotypes with – or are one mutation away from – the Tibetan wolf ("C. l. chanco") and the recently-extinct Japanese wolf ("C. l. hodophilax"). This may indicate that these canids retained the genetic signature of admixture with regional wolf populations. Another haplotype designated as S504 (47,000 YBP) from Duvanny Yar appeared on the phylogenetic tree as not being connected to wolves (both ancient and modern) yet ancestral to dogs, and may represent a genetic source for regional dogs.

In 2009, a study looked at the two earliest dog skulls that had been found at Eliseevich 1 in comparison to other much earlier but morphologically similar fossil skulls that had been found across Europe and concluded that the earlier specimens were "Paleolithic dogs", which were morphologically and genetically distinct from Pleistocene wolves that lived in Europe at that time. These also include the 36,000-year-old "Goyet dog" and the 33,000-year-old "Altai dog".
Later studies suggested that it was possible for multiple primitive forms of the dog to have existed, including in Europe. European dog populations had undergone extensive turnover during the last 15,000 years that has erased the genomic signature of early European dogs, the genetic heritage of the modern breeds has become blurred due to admixture, and there was the possibility of past domestication events that had gone extinct or had been largely replaced by more modern dog populations.

In 2016, a study compared the mitochondrial DNA and whole-genome sequences of a worldwide panel of modern dogs, the mDNA sequences of 59 ancient European dog specimens dated 14,000-3,000 YBP, and the nuclear genome sequence of a dog specimen that was found in the Late Neolithic passage grave at Newgrange, Ireland and radiocarbon dated at 4,800 YBP. A genetic analysis of the Newgrange dog showed that it was male, did not possess genetic variants associated with modern coat length nor color, was not as able to process starch as efficiently as modern dogs but more efficiently than wolves, and showed ancestry from a population of wolves that could not be found in other dogs nor wolves today. As the taxonomic classification of the "proto-dog" Paleolithic dogs as being either dogs or wolves remains controversial, they were excluded from the study. The phylogenetic tree generated from mDNA sequences found a deep division between the Sarloos wolfdog and all other dogs, indicating that breed's recent deriving from the German Shepherd and captive gray wolves. The next largest division was between Eastern Asian dogs and Western Eurasian (Europe and the Middle East) dogs that had occurred between 14,000-6,400 YBP, with the Newgrange dog clustering with the Western Eurasian dogs. The northern breed Greenland dog and the Siberian husky were poorly supported in the tree, possibly indicating mixed ancestry. (See also Taimyr wolf admixture)

The Newgrange and ancient European dog mDNA sequences could be largely assigned to mDNA haplogroups C and D but modern European dog sequences could be largely assigned to mDNA haplogroups A and B, indicating a turnover of dogs in the past from a place other than Europe. As this split dates older than the Newgrange dog this suggests that the replacement was only partial. The analysis showed that most modern European dogs had undergone a population bottleneck which can be an indicator of travel. The archaeological record shows dog remains dating over 15,000 YBP in Western Eurasia, over 12,500 YBP in Eastern Eurasia, but none older than 8,000 YBP in Central Asia. The study proposed that dogs may have been domesticated separately in both Eastern and Western Eurasia from two genetically distinct and now extinct wolf populations. East Eurasian dogs then made their way with migrating people to Western Europe between 14,000-6,400 YBP where they partially replaced the dogs of Europe. Two domestication events in Western Eurasia and Eastern Eurasia has recently been found for the domestic pig.

The hypothesis is that two genetically different, and possibly now extinct, wolf populations were domesticated independently in eastern and western Eurasia to produce paleolithic dogs. The eastern Eurasian dogs then dispersed westward alongside humans, reaching western Europe 6,400–14,000 years ago where they partially replaced the western paleolithic dogs. A single domestication is thought to be due to chance, however dual domestication on different sides of the world is unlikely to have happened randomly and it suggests that external factors - an environmental driver - may have forced wolves to work together with humans for survival. It is possible that wolves took advantage of resources that humans had, or humans may have been introduced to wolves in an area in which they didn't previously live.

The study used the radiocarbon age of the Newgrange dog to calibrate the mutation rate for dogs, which was similar to that calculated for the Late Pleistocene Taimyr wolf. Comparing the sequence of the Newgrange dog using this mutation rate with two modern wolves from Russia gave a divergence time between 20,000-60,000 YBP. However, these two modern wolves may not have been closely related to the population that gave rise to the dog, which may have diverged from their ancestor at a later time. Immediately after divergence, the dog population outnumbered the wolf population, and later the dog population underwent a population reduction to be much lower than that of the wolf.

In 2017, a study compared the nuclear genome sequences of three Neolithic dog specimens from Germany and Ireland with sequences from over 5,000 dogs and wolves. The study found that modern European dogs descended from their Neolithic ancestors with no evidence of a population turnover found by an earlier study. The study found that a single dog-wolf divergence occurred 36,900-41,500 YBP, followed by a divergence between Southeast Asian and Western Eurasian dogs 17,500-23,900 YBP and this indicates a single dog domestication event occurring between 20,000-40,000 YBP. The study did not support a dual domestication event found by an earlier study.

A 2018 study of mDNA sequences shows that the pre-Neolithic dogs of Europe all fell under haplogroup C. The Neolithic and Post-Neolithic dogs from Southeastern Europe that are associated with farmers fell under haplogroup D. In Western and Northern Europe, haplogroup D became diluted into the native dog population. This implies that haplogroup D arrived in Europe 9,000 years ago from the Near East along with pigs, cows, sheep, and goats.

The domestication of animals is the scientific theory of the mutual relationship between animals with the humans who have influence on their care and reproduction. Charles Darwin recognized the small number of traits that made domestic species different from their wild ancestors. He was also the first to recognize the difference between conscious selective breeding in which humans directly select for desirable traits, and unconscious selection where traits evolve as a by-product of natural selection or from selection on other traits.

There is a genetic difference between domestic and wild populations. There is also such a difference between the domestication traits that researchers believe to have been essential at the early stages of domestication, and the improvement traits that have appeared since the split between wild and domestic populations. Domestication traits are generally fixed within all domesticates, and were selected during the initial episode of domestication of that animal or plant, whereas improvement traits are present only in a proportion of domesticates, though they may be fixed in individual breeds or regional populations. The dog was the first domesticant and was established across Eurasia before the end of the Late Pleistocene era, well before cultivation and before the domestication of other animals.

An apex predator is a predator that sits on the top trophic level of the food chain, while a mesopredator sits further down the food chain and is dependent on smaller animals. Towards the end of the Pleistocene era, most of today's apex predators were mesopredators and this included the wolf. During the ecological upheaval associated with the close of the Late Pleistocene, one type of wolf population rose to become today's apex predator and another joined with humans to become an apex consumer.

In August 2015, a study undertook an analysis of the complete mitogenome sequences of 555 modern and ancient dogs. The sequences showed an increase in the population size approximately 23,500 YBP, which broadly coincides with the proposed separation of the ancestors of dogs and present-day wolves before the Last Glacial Maximum (refer first divergence). A ten-fold increase in the population size occurred after 15,000 YBP, which may be attributable to domestication events and is consistent with the demographic dependence of dogs on the human population (refer archaeological evidence).

Humans and wolves both exist in complex social groups. How humans and wolves got together remains unknown. One view holds that domestication as a process that is difficult to define. The term was developed by anthropologists with a human-centric view in which humans took wild animals (ungulates) and bred them to be "domestic", usually in order to provide improved food or materials for human consumption. That term may not be appropriate for a large carnivore such as the dog. This alternate view regards dogs as being either socialized and able to live among humans, or unsocialized. There exists today dogs that live with their human families but are unsocialized and will threaten strangers defensively and aggressively no different from a wild wolf. There also exists a number of cases where wild wolves have approached people in remote places, attempting to initiate play and to form companionship. One such notable wolf was Romeo, a gentle black wolf that formed relationships with the people and dogs of Juneau, Alaska. This view holds that before there could have been domestication of the wolf, there had to have been its socialization.

Animal domestication is a coevolutionary process in which a population responds to selective pressure while adapting to a novel niche that included another species with evolving behaviors.

The dog is a classic example of a domestic animal that likely traveled a commensal pathway into domestication. The dog was the first domesticant, and was domesticated and widely established across Eurasia before the end of the Pleistocene, well before cultivation or the domestication of other animals. It may have been inevitable that the first domesticated animal came from the order of carnivores as these are less afraid when approaching other species. Within the carnivores, the first domesticated animal would need to exist without an all-meat diet, possess a running and hunting ability to provide its own food, and be of a controllable size to coexist with humans, indicating the family "Canidae", and the right temperament with wolves being among the most gregarious and cooperative animals on the planet.

Ancient DNA supports the hypothesis that dog domestication preceded the emergence of agriculture and was initiated close to the Last Glacial Maximum 27,000 YBP when hunter-gatherers preyed on megafauna, and when proto-dogs might have taken advantage of carcasses left on site by early hunters, assisted in the capture of prey, or provided defense from large competing predators at kill-sites. Wolves were probably attracted to human campfires by the smell of meat being cooked and discarded refuse in the vicinity, first loosely attaching themselves and then considering these as part of their home territory where their warning growls would alert humans to the approach of outsiders. The wolves most likely drawn to human camps were the less-aggressive, subdominant pack members with lowered flight response, higher stress thresholds, less wary around humans, and therefore better candidates for domestication. The earliest sign of domestication in dogs was the neotonization of skull morphology and the shortening of snout length that results in tooth crowding, reduction in tooth size, and a reduction in the number of teeth, which has been attributed to the strong selection for reduced aggression. This process may have begun during the initial commensal stage of dog domestication, even before humans began to be active partners in the process.

A maternal mitochondrial, paternal Y chromosome, and microsatellite assessment of two wolf populations in North America and combined with satellite telemetry data revealed significant genetic and morphological differences between one population that migrated with and preyed upon caribou, and another territorial ecotype population that remained in a boreal coniferous forest. Though these two populations spend a period of the year in the same place, and though there was evidence of gene flow between them, the difference in prey–habitat specialization has been sufficient to maintain genetic and even coloration divergence. A study has identified the remains of a population of extinct Pleistocene Beringian wolves with unique mitochondrial signatures. The skull shape, tooth wear, and isotopic signatures suggested these were specialist megafauna hunters and scavengers that became extinct while less specialized wolf ecotypes survived. Analogous to the modern wolf ecotype that has evolved to track and prey upon caribou, a Pleistocene wolf population could have begun following mobile hunter-gatherers, thus slowly acquiring genetic and phenotypic differences that would have allowed them to more successfully adapt to the human habitat.

Even today, the wolves on Ellesmere Island do not fear humans, which is thought to be due to them seeing humans so little, and they will approach humans cautiously, curiously and closely.

Some studies have found greater diversity in the genetic markers of dogs from East and Central Asia compared to Europe and have concluded that dogs originated from these regions, despite no archaeological evidence to support the conclusions. One reason for these discrepancies is the sustained admixture between different dog and wolf populations across the Old and New Worlds over at least the last 10,000 years, which has blurred the genetic signatures and confounded efforts of researchers at pinpointing the origins of dogs. Another reason is that none of the modern wolf populations are related to the Pleistocene wolves that were first domesticated. In other words, the extinction of the wolves that were the direct ancestors of dogs has muddied efforts to pinpoint the time and place of dog domestication.

Phylogenetic analysis shows that modern dog mDNA haplotypes resolve into four monophyletic clades with strong statistical support, and these have been designated by researchers as clades A-D. Other studies that included a wider sample of specimens have reported two rare East Asian clades E-F with weaker statistical support. In 2009, a study found that haplogroups A, B and C included 98% of dogs and are found universally distributed across Eurasia, indicating that they were the result of a single domestication event, and that haplogroups D, E, and F were rare and appeared to be the result of regional hybridization with local wolves post-domestication. Haplogroups A and B contained subclades that appeared to be the result of hybridization with wolves post-domestication, because each haplotype within each of these subclades was the result of a female wolf/male dog pairing.

Haplogroup A: Includes 64-65% of dogs. Haplotypes of subclades a2–a6 are derived from post-domestication wolf–dog hybridization.

Haplogroup B: Includes 22-23% of dogs. haplotypes of subclade b2 are derived from post-domestication wolf–dog hybridization.

Haplogroup C: Includes 10-12% of dogs.

Haplogroup D: Derived from post-domestication wolf–dog hybridization in subclade d1 (Scandinavia) and d2 (South-West Asia). The northern Scandinavian subclade d1 hybrid haplotypes originated 480-3,000 YBP and are found in all Sami-related breeds: Finnish Lapphund, Swedish Lapphund, Lapponian Herder, Jamthund, Norwegian Elkhound and Hällefors Elkhound. The maternal wolf sequence that contributed to them has not been matched across Eurasia and its branch is phylogenetically rooted in the same sequence as the Altai dog (not a direct ancestor). The subclade d2 hybrid haplotypes are found in 2.6% of South-West Asian dogs.

Haplogroup E: Derived from post-domestication wolf–dog hybridization in East Asia, (rare distribution in South-East Asia, Korea and Japan).

Haplogroup F: Derived from post-domestication wolf–dog hybridization in Japan. A study of 600 dog specimens found only one dog whose sequence indicated hybridization with the extinct Japanese wolf.

It is not known whether this hybridization was the result of humans selecting for phenotypic traits from local wolf populations or the result of natural introgression as the dog expanded across Eurasia.

In 2018, a study found a small amount of dog ancestry in 62% of Eurasian wolf specimens looked at, that hybridization had occurred across a wide number of timescales and not just recently, however in contrast there was almost no admixture detected in the North American specimens. There was introgression of the male dog into the wolf, but also one hybrid detected which was the result of a male wolf crossed with a female dog. Wolves have maintained their phenotype differences from the dog, which indicates low-frequency hybridization. The conclusion is that phenotype is no indication of "purity" and the definition of pure wolves is ambiguous. Free-ranging dogs across Eurasia show introgression from wolves. Another study found that the β-defensin gene responsible for the black coat of North American wolves was the result of a single introgression from dogs in the Yukon dated between 1,600-7,200 years ago. The study proposes that early Native American dogs were the source.

In May 2015, a study compared the ancestry of the Taimyr-1 wolf lineage to that of dogs and gray wolves.

Comparison to the gray wolf lineage indicated that Taimyr-1 was basal to gray wolves from the Middle East, China, Europe and North America but shared a substantial amount of history with the present-day gray wolves after their divergence from the coyote. This implies that the ancestry of the majority of gray wolf populations today stems from an ancestral population that lived less than 35,000 years ago but before the inundation of the Bering Land Bridge with the subsequent isolation of Eurasian and North American wolves.

A comparison of the ancestry of the Taimyr-1 lineage to the dog lineage indicated that some modern dog breeds have a closer association with either the gray wolf or Taimyr-1 due to admixture. The Saarloos wolfdog showed more association with the gray wolf, which is in agreement with the documented historical crossbreeding with gray wolves in this breed. Taimyr-1 shared more alleles (i.e. gene expressions) with those breeds that are associated with high latitudes - the Siberian husky and Greenland dog that are also associated with arctic human populations, and to a lesser extent the Shar Pei and Finnish spitz. An admixture graph of the Greenland dog indicates a best-fit of 3.5% shared material, although an ancestry proportion ranging between 1.4% and 27.3% is consistent with the data. This indicates admixture between the Taimyr-1 population and the ancestral dog population of these four high-latitude breeds. These results can be explained either by a very early presence of dogs in northern Eurasia or by the genetic legacy of Taimyr-1 being preserved in northern wolf populations until the arrival of dogs at high latitudes. This introgression could have provided early dogs living in high latitudes with phenotypic variation beneficial for adaption to a new and challenging environment. It also indicates that the ancestry of present-day dog breeds descends from more than one region.

An attempt to explore admixture between Taimyr-1 and gray wolves produced unreliable results.

As the Taimyr wolf had contributed to the genetic makeup of the Arctic breeds, a later study suggested that descendants of the Taimyr wolf survived until dogs were domesticated in Europe and arrived at high latitudes where they mixed with local wolves, and these both contributed to the modern Arctic breeds. Based on the most widely accepted oldest zooarchaeological dog remains, domestic dogs most likely arrived at high latitudes within the last 15,000 years. The mutation rates calibrated from both the Taimyr wolf and the Newgrange dog genomes suggest that modern wolf and dog populations diverged from a common ancestor between 20,000 and 60,000 YBP. This indicates that either dogs were domesticated much earlier than their first appearance in the archaeological record, or they arrived in the Arctic early, or both.

Charles Darwin recognized the small number of traits that made domestic species different from their wild ancestors. He was also the first to recognize the difference between conscious selective breeding in which humans directly select for desirable traits, and unconscious selection where traits evolve as a by-product of natural selection or from selection on other traits. Domestic animals have variations in coat color as well as texture, dwarf and giant varieties, and changes in their reproductive cycle, and many others have tooth crowding and floppy ears.

Although it is easy to assume that each of these traits was uniquely selected for by hunter-gatherers and early farmers, beginning in 1959 Dmitry Belyayev tested the reactions of silver foxes to a hand placed in their cage and selected the tamest, least aggressive individuals to breed. His hypothesis was that, by selecting a behavioral trait, he could also influence the phenotype of subsequent generations, making them more domestic in appearance. Over the next 40 years, he succeeded in producing foxes with traits that were never directly selected for, including piebald coats floppy ears, upturned tails, shortened snouts, and shifts in developmental timing. In the 1980s, a researcher used a set of behavioral, cognitive, and visible phenotypic markers, such as coat colour, to produce domesticated fallow deer within a few generations. Similar results for tameness and fear have been found for mink and Japanese quail. In addition to demonstrating that domestic phenotypic traits could arise through selection for a behavioral trait, and domestic behavioral traits could arise through the selection for a phenotypic trait, these experiments provided a mechanism to explain how the animal domestication process could have begun without deliberate human forethought and action.

The genetic difference between domestic and wild populations can be framed within two considerations. The first distinguishes between domestication traits that are presumed to have been essential at the early stages of domestication, and improvement traits that have appeared since the split between wild and domestic populations. Domestication traits are generally fixed within all domesticates and were selected during the initial episode of domestication, whereas improvement traits are present only in a proportion of domesticates, though they may be fixed in individual breeds or regional populations. A second issue is whether traits associated with the domestication syndrome resulted from a relaxation of selection as animals exited the wild environment or from positive selection resulting from intentional and unintentional human preference. Some recent genomic studies on the genetic basis of traits associated with the domestication syndrome have shed light on both of these issues. A study published in 2016 suggested that there have been negative genetic consequences of the domestication process as well, that enrichment of disease-related gene variants accompanied positively selected traits.

In 2010, a study identified 51 regions of the dog genome that were associated with phenotypic variation among breeds in 57 traits studied, which included body, cranial, dental, and long bone shape and size. There were 3 quantitative trait loci that explained most of the phenotypic variation. Indicators of recent selection were shown by many of the 51 genomic regions that were associated with traits that define a breed, which include body size, coat characteristics, and ear floppiness. Geneticists have identified more than 300 genetic loci and 150 genes associated with coat color variability. Knowing the mutations associated with different colors has allowed the correlation between the timing of the appearance of variable coat colors in horses with the timing of their domestication. Other studies have shown how human-induced selection is responsible for the allelic variation in pigs. Together, these insights suggest that, although natural selection has kept variation to a minimum before domestication, humans have actively selected for novel coat colors as soon as they appeared in managed populations.

In 2015, a study looked at over 100 pig genome sequences to ascertain their process of domestication. A model that fitted the data included admixture with a now extinct ghost population of wild pigs during the Pleistocene. The study also found that despite back-crossing with wild pigs, the genomes of domestic pigs have strong signatures of selection at genetic loci that affect behavior and morphology. The study concluded that human selection for domestic traits likely counteracted the homogenizing effect of gene flow from wild boars and created domestication islands in the genome. The same process may also apply to other domesticated animals.

In 2014, a whole genome study of the DNA differences between wolves and dogs found that dogs did not show a reduced fear response but did show greater synaptic plasticity. Synaptic plasticity is widely believed to be the cellular correlate of learning and memory, and this change may have altered the learning and memory abilities of dogs in comparison to wolves.

Unlike other domestic species which were primarily selected for production-related traits, dogs were initially selected for their behaviors. In 2016, a study found that there were only 11 fixed genes that showed variation between wolves and dogs. These gene variations were unlikely to have been the result of natural evolution, and indicate selection on both morphology and behavior during dog domestication. There was evidence of selection during dog domestication of genes that affect the adrenaline and noradrenaline biosynthesis pathway. These genes are involved in the synthesis, transport and degradation of a variety of neurotransmitters, particularly the catecholamines, which include dopamine and noradrenaline. Recurrent selection on this pathway and its role in emotional processing and the fight-or-flight response suggests that the behavioral changes we see in dogs compared to wolves may be due to changes in this pathway, leading to tameness and an emotional processing ability. Dogs generally show reduced fear and aggression compared to wolves. Some of these genes have been associated with aggression in some dog breeds, indicating their importance in both the initial domestication and then later in breed formation.

In 2018, a study identified 429 genes that differed between modern dogs and modern wolves. As the differences in these genes could also be found in ancient dog fossils, these were regarded as being the result of the initial domestication and not from recent breed formation. These genes are linked to neural crest and central nervous system development. These genes affect embryogenesis and can confer tameness, smaller jaws, floppy ears, and diminished craniofacial development, which distinguish domesticated dogs from wolves and are considered to reflect domestication syndrome. The study proposes that domestication syndrome is caused by alterations in the migration or activity of neural crest cells during their development. The study concluded that during early dog domestication, the initial selection was for behavior. This trait is influenced by those genes which act in the neural crest, which led to the phenotypes observed in modern dogs.

AMY2B (Alpha-Amylase 2B) is a gene that codes a protein that assists with the first step in the digestion of dietary starch and glycogen. An expansion of this gene in dogs would enable early dogs to exploit a starch-rich diet as they fed on refuse from agriculture. In a study in 2014, the data indicated that the wolves and dingo had just two copies of the gene and the Siberian Husky that is associated with hunter-gatherers had just three or four copies, whereas the Saluki that is associated with the Fertile Crescent where agriculture originated had 29 copies. The results show that on average, modern dogs have a high copy number of the gene, whereas wolves and dingoes do not. The high copy number of AMY2B variants likely already existed as a standing variation in early domestic dogs, but expanded more recently with the development of large agriculturally based civilizations. This suggests that at the beginning of the domestication process, dogs may have been characterized by a more carnivorous diet than their modern-day counterparts, a diet held in common with early hunter-gatherers. A later study indicated that because most dogs had a high copy number of the AMY2B gene but the arctic breeds and the dingo did not, that the dog's dietary change may not have been caused by initial domestication but by the subsequent spread of agriculture to most - but not all - regions of the planet.

In 2016, a study of the dog genome compared to the wolf genome looked for genes that showed signs of having undergone positive selection. The study identified genes relating to brain function and behavior, and to lipid metabolism. This ability to process lipids indicates a dietary target of selection that was important when proto-dogs hunted and fed alongside hunter-gatherers. The evolution of the dietary metabolism genes may have helped process the increased lipid content of early dog diets as they scavenged on the remains of carcasses left by hunter-gatherers. Prey capture rates may have increased in comparison to wolves and with it the amount of lipid consumed by the assisting proto-dogs. A unique dietary selection pressure may have evolved both from the amount consumed, and the shifting composition of, tissues that were available to proto-dogs once humans had removed the most desirable parts of the carcass for themselves. A study of the mammal biomass during modern human expansion into the northern Mammoth steppe found that it had occurred under conditions of unlimited resources, and that many of the animals were killed with only a small part consumed or left unused.

Dogs can infer the name of an object and have been shown to learn the names of over 1,000 objects. Dogs can follow the human pointing gesture; even nine-week-old puppies can follow a basic human pointing gesture without being taught. New Guinea singing dogs, a half-wild proto-dog endemic to the remote alpine regions of New Guinea, as well as dingoes in the remote Outback of Australia are also capable of this. These examples demonstrate an ability to read human gestures that arose early in domestication and did not require human selection. "Humans did not develop dogs, we only fine-tuned them down the road."

A dog's cranium is 15% smaller than an equally heavy wolf's, and the dog is less aggressive and more playful. Other species pairs show similar differences. Bonobos, like chimpanzees, are a close genetic cousin to humans, but unlike the chimpanzees, bonobos are not aggressive and do not participate in lethal inter-group aggression or kill within their own group. The most distinctive features of a bonobo are its cranium, which is 15% smaller than a chimpanzee's, and its less aggressive and more playful behavior. In other examples, the guinea pig's cranium is 13% smaller than its wild cousin the cavy, and domestic fowl show a similar reduction to their wild cousins. Possession of a smaller cranium for holding a smaller brain is a telltale sign of domestication. Bonobos appear to have domesticated themselves. In the farm fox experiment, humans selectively bred foxes against aggression, causing domestication syndrome. The foxes were not selectively bred for smaller craniums and teeth, floppy ears, or skills at using human gestures, but these traits were demonstrated in the friendly foxes. Natural selection favors those that are the most successful at reproducing, not the most aggressive. Selection against aggression made possible the ability to cooperate and communicate among foxes, dogs and bonobos. Perhaps it did the same thing for humans. The more docile animals have been found to have less testosterone than their more aggressive counterparts, and testosterone controls aggression and brain size. One researcher has argued that in becoming more social, we humans have developed a smaller brain than those of humans 20,000 years ago.

As a result of the domestication process there is also evidence of convergent evolution having occurred between dogs and humans. The history of the two is forever intertwined.

In 2007, a study found that dog domestication was accompanied by selection at three genes with key roles in starch digestion: AMY2B, MGAMand SGLT1, and was a striking case of parallel evolution when coping with an increasingly starch-rich diet caused similar adaptive responses in dogs and humans.

In 2013, a DNA sequencing study indicated that parallel evolution in humans and dogs is most apparent in the genes for digestion and metabolism, neurological processes, and cancer, likely as a result of shared selection pressures.

In 2014, a study compared the hemoglobin levels of village dogs and people on the Chinese lowlands with those on the Tibetan Plateau. It found the hemoglobin levels higher for both people and dogs in Tibet, suggesting that Tibetan dogs might share similar adaptive strategies as the Tibetan people. A population genetic analysis then showed a significant convergence between humans and dogs in Tibet. Like the Tibetan people, Tibetan mastiffs appear to have derived these benefits partially from the EPAS1 gene, acquired through introgression.

In 2015, a study found that when dogs and their owners interact, extended eye contact (mutual gaze) increases oxytocin levels in both the dog and its owner. As oxytocin is known for its role in maternal bonding, it is considered likely that this effect has supported the coevolution of human-dog bonding. One observer has stated, "The dog could have arisen only from animals predisposed to human society by lack of fear, attentiveness, curiosity, necessity, and recognition of advantage gained through collaboration...the humans and wolves involved in the conversion were sentient, observant beings constantly making decisions about how they lived and what they did, based on the perceived ability to obtain at a given time and place what they needed to survive and thrive. They were social animals willing, even eager, to join forces with another animal to merge their sense of group with the others' sense and create an expanded super-group that was beneficial to both in multiple ways. They were individual animals and people involved, from our perspective, in a biological and cultural process that involved linking not only their lives but the evolutionary fate of their heirs in ways, we must assume, they could never have imagined. Powerful emotions were in play that many observers today refer to as love – boundless, unquestioning love."

Convergent evolution is when distantly related species independently evolve similar solutions to the same problem. For example, fish, penguins and dolphins have each separately evolved flippers as a solution to the problem of moving through the water. What has been found between dogs and humans is something less frequently demonstrated: psychological convergence. Dogs have independently evolved to be cognitively more similar to humans than we are to our closest genetic relatives. Dogs have evolved specialized skills for reading human social and communicative behavior. These skills seem more flexible – and possibly more human-like – than those of other animals more closely related to humans phylogenetically, such as chimpanzees, bonobos and other great apes. This raises the possibility that convergent evolution has occurred: both "Canis familiaris" and "Homo sapiens" might have evolved some similar (although obviously not identical) social-communicative skills – in both cases adapted for certain kinds of social and communicative interactions with human beings.

The pointing gesture is a human-specific signal, is referential in its nature, and is a foundation building-block of human communication. Human infants acquire it weeks before the first spoken word. In 2009, a study compared the responses to a range of pointing gestures by dogs and human infants. The study showed little difference in the performance of 2-year-old children and dogs, while 3-year-old children's performance was higher. The results also showed that all subjects were able to generalize from their previous experience to respond to relatively novel pointing gestures. These findings suggest that dogs demonstrating a similar level of performance as 2-year-old children can be explained as a joint outcome of their evolutionary history as well as their socialization in a human environment.

Later studies support coevolution in that dogs can discriminate the emotional expressions of human faces, and that most people can tell from a bark whether a dog is alone, being approached by a stranger, playing, or being aggressive, and can tell from a growl how big the dog is.

In 2002, a study proposed that immediate human ancestors and wolves may have domesticated each other through a strategic alliance that would change both respectively into humans and dogs. The effects of human psychology, hunting practices, territoriality and social behavior would have been profound. Wolves and dogs mark their territory with scent; however, humans do not have a keen sense of smell and may have begun to mark their territories with symbols, which became the first art and may have been generative of human culture. Wolves hunt large game; however, there is no evidence of pre-"sapiens" hunting large game. Early humans moved from scavenging and small-game hunting to big-game hunting by living in larger, socially more-complex groups, learning to hunt in packs, and developing powers of cooperation and negotiation in complex situations. As these are characteristics of wolves, dogs and humans, it can be argued that these behaviors were enhanced once wolves and humans began to cohabit. Communal hunting led to communal defense. Wolves actively patrol and defend their scent-marked territory, and perhaps humans had their sense of territoriality enhanced by living with wolves. One of the keys to recent human survival has been the forming of partnerships. Strong bonds exist between same-sex wolves, dogs and humans and these bonds are stronger than exist between other same-sex animal pairs. Today, the most widespread form of inter-species bonding occurs between humans and dogs. The concept of friendship has ancient origins but it may have been enhanced through the inter-species relationship to give a survival advantage.

In 2003, a study compared the behavior and ethics of chimpanzees, wolves and humans. Cooperation among humans' closest genetic relative is limited to occasional hunting episodes or the persecution of a competitor for personal advantage, which had to be tempered if humans were to become domesticated. The closest approximation to human morality that can be found in nature is that of the gray wolf, "Canis lupus". Wolves are among the most gregarious and cooperative of animals on the planet, and their ability to cooperate in well-coordinated drives to hunt prey, carry items too heavy for an individual, provisioning not only their own young but also the other pack members, babysitting etc. are rivaled only by that of human societies. Similar forms of cooperation are observed in two closely related canids, the African wild dog and the Asian dhole, therefore it is reasonable to assume that canid sociality and cooperation are old traits that in terms of evolution predate human sociality and cooperation. Today's wolves may even be less social than their ancestors, as they have lost access to big herds of ungulates and now tend more toward a lifestyle similar to coyotes, jackals, and even foxes. Social sharing within families may be a trait that early humans learned from wolves, and with wolves digging dens long before humans constructed huts it is not clear who domesticated whom.

On the mammoth steppe the wolf's ability to hunt in packs, to share risk fairly among pack members, and to cooperate moved them to the top of the food chain above lions, hyenas and bears. Some wolves followed the great reindeer herds, eliminating the unfit, the weaklings, the sick and the aged, and therefore improved the herd. These wolves had become the first pastoralists hundreds of thousands of years before humans also took to this role. The wolves' advantage over their competitors was that they were able to keep pace with the herds, move fast and enduringly, and make the most efficient use of their kill by their ability to "wolf down" a large part of their quarry before other predators had detected the kill. The study proposed that during the Last Glacial Maximum, some of our ancestors teamed up with those pastoralist wolves and learned their techniques. Many of our ancestors remained gatherers and scavengers, or specialized as fish-hunters, hunter-gatherers, and hunter-gardeners. However, some ancestors adopted the pastoralist wolves' lifestyle as herd followers and herders of reindeer, horses, and other hoofed animals. They harvested the best stock for themselves while the wolves kept the herd strong, and this group of humans was to become the first herders and this group of wolves was to become the first dogs.

The domestic dog is the most widely abundant large carnivore. The dog was the first species and the only large carnivore to have been domesticated. Over the past 200 years, dogs have undergone rapid phenotypic change and were formed into today's modern dog breeds due to artificial selection imposed by humans. These breeds can vary in size and weight from a teacup poodle to a giant mastiff. The skull, body, and limb proportions vary significantly between breeds, with dogs displaying more phenotypic diversity than can be found within the entire order of carnivores. Some breeds demonstrate outstanding skills in herding, retrieving, scent detection, and guarding, which demonstrates the functional and behavioral diversity of dogs. There have been major advances in understanding the genes that gave rise to the phenotypic traits of dogs. The first dogs were certainly wolflike, however the phenotypic changes that coincided with the dog–wolf genetic divergence are not known.

In 1914, on the eve of the First World War, two human skeletons were discovered during basalt quarrying at Oberkassel, Bonn in Germany. With them were found a right mandible of a "wolf" and other animal bones. After the end of the First World War, in 1919 a full study was made of these remains. The mandible was recorded as ""Canis lupus", the wolf" and some of the other animal bones were assigned to it. The remains were then stored and forgotten for fifty years. In the late 1970s there was renewed interest in the Oberkassel remains and the mandible was re-examined and reclassified as belonging to a domesticated dog. The mitochondrial DNA sequence of the mandible was matched to "Canis lupus familiaris" - dog, and confirms that the Oberkassel dog is a direct ancestor of today's dogs. The bodies were dated to 14,223 YBP. This implies that in Western Europe there were morphologically and genetically "modern" dogs in existence around 14,500 years ago.

Later studies assigned more of the other animal bones to the dog until most of a skeleton could be assembled. The humans were a man aged 40 years and a woman aged 25 years. All three skeletal remains were found covered with large 20 cm thick basalt blocks and were sprayed with red hematite powder. The consensus is that a dog was buried along with two humans. A tooth belonging to a smaller and older dog was also identified but it had not been sprayed with red powder. The cause of the death of the two humans is not known. A pathology study of the dog remains suggests that it had died young after suffering from canine distemper between ages 19 and 23 weeks. The dog could not have survived during this period without intensive human care. During this period the dog was of no utilitarian use to humans, and suggests the existence of emotional or symbolic ties between these humans and this dog. In conclusion, near the end of the Late Pleistocene at least some humans regarded dogs not just materialistically, but had developed emotional and caring bonds for their dogs.

During the late Paleolithic, the increase in human population density, advances in blade and hunting technology, and climate change may have altered prey densities and made scavenging crucial to the survival of some wolf populations. Adaptations to scavenging such as tameness, small body size, and a decreased age of reproduction would reduce their hunting efficiency further, eventually leading to obligated scavenging. Whether these earliest dogs were simply human-commensal scavengers or they played some role as companions or hunters that hastened their spread is unknown.

Researchers have proposed that in the past a hunting partnership existed between humans and dogs that was the basis for dog domestication. The transition from the Late Pleistocene into the early Holocene was marked by climatic change from cold and dry to warmer, wetter conditions and rapid shifts in flora and fauna, with much of the open habitat of large herbivores being replaced by forests. In the early Holocene, it is proposed that along with changes in arrow-head technology that hunting dogs were used by hunters to track and retrieve wounded game in thick forests. The dog's ability to chase, track, sniff out and hold prey can significantly increase the success of hunters in forests, where human senses and location skills are not as sharp as in more open habitats. Dogs are still used for hunting in forests today.

In Japan, temperate deciduous forests rapidly spread onto the main island of Honshu and caused an adaption away from hunting megafauna (Naumann's elephant and Yabe's giant deer) to hunting the quicker sika deer and wild boar in dense forest. With this came a change in hunting technology, including a shift to smaller, triangular points for arrows. A study of the Jōmon people that lived on the Pacific coast of Honshu during the early Holocene shows that they were conducting individual dog burials and were probably using dogs as tools for hunting sika deer and wild boar, as hunters in Japan still do today.

Hunting dogs make major contributions to forager societies and the ethnographic record shows them being given proper names, treated as family members, and considered separate to other types of dogs. This special treatment includes separate burials with markers and grave-goods, with those that were exceptional hunters or that were killed on the hunt often venerated. A dog's value as a hunting partner gives them status as a living weapon and the most skilled elevated to taking on a "personhood", with their social position in life and in death similar to that of the skilled hunters.

Intentional dog burials together with ungulate hunting is also found in other early Holocene deciduous forest forager societies in Europe and North America, indicating that across the Holarctic temperate zone hunting dogs were a widespread adaptation to forest ungulate hunting.

In 2018, a study compared sequences of fossil North American dogs with fossil Siberian dogs and modern dogs. The study indicates that dogs entered North America from Siberia 4,500 years after humans did, were isolated for 9,000 years, and after contact with Europeans these no longer exist because they were replaced with Eurasian dogs. The pre-contact dogs exhibit a unique genetic signature that is also now gone, with their nearest genetic relatives being the arctic breed dogs.

In 2017, a study showed that 9,000 YBP the domestic dog was present at what is now Zhokhov Island, arctic north-eastern Siberia, which was connected to the mainland at that time. The dogs were selectively bred as either sled dogs or as hunting dogs, which implies that a sled dog standard and a hunting dog standard existed at that time. The optimal maximum size for a sled dog is 20–25 kg based on thermo-regulation, and the ancient sled dogs were between 16–25 kg. The same standard has been found in the remains of sled dogs from this region 2,000 YBP and in the modern Siberian husky breed standard. Other dogs were more massive at 30 kg and appear to be dogs that had been crossed with wolves and used for polar bear hunting. At death, the heads of the dogs had been carefully separated from their bodies by humans, probably for ceremonial reasons.

The study proposes that after having diverged from the common ancestor along with the grey wolf, the evolution of "Canis familiaris" proceeded in three stages. The first was natural selection based on feeding behavior within the ecological niche that had been formed through human activity. The second was artificial selection based on tamability. The third was directed selection based on forming breeds that possessed qualities to help with specific tasks within the human economy. The process commenced 40,000-30,000 YBP with its speed increasing with each stage until domestication became complete.

Along with sheep, goats were among the first domesticated animals. The domestication process started at least 10,000 years ago in what is now northern Iran. Easy human access to goat hair, meat, and milk were the primary motivations. Goat skins were popularly used until the Middle Ages for water and wine bottles when traveling and camping, and in certain regions as parchment for writing.

Capra (genus)

Capra is a genus of mammals, the goats, composed of up to nine species, including the wild goat, the markhor, and several species known as ibexes. The domestic goat ("Capra aegagrus hircus") is a domesticated subspecies of the wild goat ("Capra aegagrus"). Evidence of goat domestication dates back more than 8,500 years.

Wild goats are animals of mountain habitats. They are very agile and hardy, able to climb on bare rock and survive on sparse vegetation. They can be distinguished from the genus "Ovis", which includes sheep, by the presence of scent glands close to the feet, in the groin, and in front of the eyes, and the absence of other facial glands, and by the presence of a beard in the males, and of hairless calluses on the knees of the forelegs.

The Rocky Mountain goat is in a separate genus, "Oreamnos". Present-day genetic and phenotypic differences between the "Capra" species are largely related to (1) discontinuity of and impeded migration between "Capra" populations during glacial periods, and (2) insufficient time in the postglacial period for now-adjoining "Capra" populations to overcome behavioral mechanisms impeding hybridization in the wild so as to erase these differences.

All members of the genus "Capra" are bovids (members of the family Bovidae), and more specifically caprids (subfamily Caprinae). As such they are ruminants, meaning they chew the cud, and have four-chambered stomachs which play a vital role in digesting, regurgitating, and redigesting their food.

The genus has sometimes been taken to include "Ovis" (sheep) and "Ammotragus" (Barbary sheep), but these are usually regarded as distinct genera, leaving "Capra" for goats and ibexes. In this smaller genus, some authors have recognized only two species, the markhor on one side and all other forms included in one species on the other side. Today, nine species are usually accepted:

The goats of the genus "Capra" have complex systematic relationships, which are still not completely resolved. Recent studies based on mitochondrial DNA suggest that the Siberian ibex and the Nubian ibex represent distinct species, which are not very closely related to the physically similar Alpine ibex. The Alpine ibex forms a group with the Spanish ibex. The West Caucasian tur appears to be more closely related to the wild goat than to the East Caucasian tur. The markhor is relatively little separated from other forms—previously it had been considered to be a separate branch of the genus.

Almost all wild goat species are allopatric (geographically separated)—the only geographical overlaps are the wild goat ("Capra hircus") with the East Caucasian tur ("Capra caucasica cylindricornis"), and the markhor ("Capra falconeri") with the Siberian ibex ("Capra siberica"). In both cases, the overlapping species do not usually interbreed in the wild, but in captivity, all "Capra" species can interbreed, producing fertile offspring.

A study by Queen Mary University reports that goats try to communicate with people in the same manner as domesticated animals such as dogs and horses. Goats were first domesticated as livestock more than 10,000 years ago. Research conducted to test communication skills found that the goats will look to a human for assistance when faced with a challenge that had previously been mastered, but was then modified. Specifically, when presented with a box, the goat was able to remove the lid and retrieve a treat inside, but when the box was turned so the lid could not be removed, the goat would turn and gaze at the person and move toward them, before looking back toward the box. This is the same type of complex communication observed by animals bred as domestic pets, such as dogs. Researchers believe that better understanding of human-goat interaction could offer overall improvement in the animals' welfare. The field of anthrozoology has established that domesticated animals have the capacity for complex communication with humans when in 2015 a Japanese scientist determined that levels of oxytocin did increase in human subjects when dogs were exposed to a dose of the "love hormone", proving that a human-animal bond does exist. This is the same affinity that was proven with the London study above; goats are intelligent, capable of complex communication, and able to form bonds. Despite having the reputation of being slightly rebellious, more and more people today are choosing more exotic companion animals like goats. Goats are herd animals and typically prefer the company of other goats, but because of their herd mentality, they will follow their owners around just the same.

Goat

The domestic goat or simply goat ("Capra aegagrus hircus") is a subspecies of "C. aegagrus" domesticated from the wild goat of Southwest Asia and Eastern Europe. The goat is a member of the animal family Bovidae and the goat—antelope subfamily Caprinae, meaning it is closely related to the sheep. There are over 300 distinct breeds of goat. Goats are one of the oldest domesticated species of animal, and have been used for milk, meat, fur, and skins across much of the world. Milk from goats is often turned into goat cheese.

Female goats are referred to as "does" or "nannies", intact males are called "bucks" or "billies" and juvenile goats of both sexes are called "kids". Castrated males are called "wethers". While the words "hircine" and "caprine" both refer to anything having a goat-like quality, "hircine" is used most often to emphasize the distinct smell of domestic goats.

In 2011, there were more than 924 million goats living in the world, according to the UN Food and Agriculture Organization.

The Modern English word "goat" comes from Old English "gāt" "she-goat, goat in general", which in turn derives from Proto-Germanic *"gaitaz" (cf. Dutch/Icelandic "geit", German "Geiß", and Gothic "gaits"), ultimately from Proto-Indo-European "*ǵʰaidos" meaning "young goat" (cf. Latin "haedus" "kid"), itself perhaps from a root meaning "jump" (assuming that Old Church Slavonic "zajęcǐ" "hare", Sanskrit "jihīte" "he moves" are related). To refer to the male, Old English used "bucca" (giving modern "buck") until ousted by "hegote", "hegoote" in the late 12th century. "Nanny goat" (females) originated in the 18th century and "billy goat" (for males) in the 19th.

Goats are among the earliest animals domesticated by humans. The most recent genetic analysis confirms the archaeological evidence that the wild Bezoar ibex of the Zagros Mountains is the likely original ancestor of probably all domestic goats today.

Neolithic farmers began to herd wild goats primarily for easy access to milk and meat, as well as to their dung, which was used as fuel, and their bones, hair and sinew for clothing, building and tools. The earliest remnants of domesticated goats dating 10,000 years before present are found in Ganj Dareh in Iran. Goat remains have been found at archaeological sites in Jericho, Choga Mami, Djeitun, and Çayönü, dating the domestication of goats in Western Asia at between 8000 and 9000 years ago.

Studies of DNA evidence suggests 10,000 years BP as the domestication date.

Historically, goat hide has been used for water and wine bottles in both traveling and transporting wine for sale. It has also been used to produce parchment.

Each recognized breed of goat has specific weight ranges, which vary from over for bucks of larger breeds such as the Boer, to for smaller goat does. Within each breed, different strains or bloodlines may have different recognized sizes. At the bottom of the size range are miniature breeds such as the African Pygmy, which stand at the shoulder as adults.

Most goats naturally have two horns, of various shapes and sizes depending on the breed. There have been incidents of polycerate goats (having as many as eight horns), although this is a genetic rarity thought to be inherited. Unlike cattle, goats have not been successfully bred to be reliably polled, as the genes determining sex and those determining horns are closely linked. Breeding together two genetically polled goats results in a high number of intersex individuals among the offspring, which are typically sterile. Their horns are made of living bone surrounded by keratin and other proteins, and are used for defense, dominance, and territoriality.

Goats are ruminants. They have a four-chambered stomach consisting of the rumen, the reticulum, the omasum, and the abomasum. As with other mammal ruminants, they are even-toed ungulates. The females have an udder consisting of two teats, in contrast to cattle, which have four teats. An exception to this is the Boer goat, which sometimes may have up to eight teats.

Goats have horizontal, slit-shaped pupils. Because goats' irises are usually pale, their contrasting pupils are much more noticeable than in animals such as cattle, deer, most horses and many sheep, whose similarly horizontal pupils blend into a dark iris and sclera.

Both male and female goats have beards, and many types of goat (most commonly dairy goats, dairy-cross Boers, and pygmy goats) may have wattles, one dangling from each side of the neck.

Goats expressing the tan pattern have coats pigmented completely with phaeomelanin (tan/brown pigment). The allele which codes for this pattern is located at the agouti locus of the goat genome. It is completely dominant to all other alleles at this locus. There are multiple modifier genes which control how much tan pigment is actually expressed, so a tan-patterned goat can have a coat ranging from pure white to deep red.

Goats reach puberty between three and 15 months of age, depending on breed and nutritional status. Many breeders prefer to postpone breeding until the doe has reached 70% of the adult weight. However, this separation is rarely possible in extensively managed, open-range herds.

In temperate climates and among the Swiss breeds, the breeding season commences as the day length shortens, and ends in early spring or before. In equatorial regions, goats are able to breed at any time of the year. Successful breeding in these regions depends more on available forage than on day length. Does of any breed or region come into estrus (heat) every 21 days for two to 48 hours. A doe in heat typically flags (vigorously wags) her tail often, stays near the buck if one is present, becomes more vocal, and may also show a decrease in appetite and milk production for the duration of the heat.

Bucks (intact males) of Swiss and northern breeds come into rut in the fall as with the does' heat cycles. Bucks of equatorial breeds may show seasonal reduced fertility, but as with the does, are capable of breeding at all times. Rut is characterized by a decrease in appetite and obsessive interest in the does. A buck in rut will display flehmen lip curling and will urinate on his forelegs and face. Sebaceous scent glands at the base of the horns add to the male goat's odor, which is important to make him attractive to the female. Some does will not mate with a buck which has been descented.

In addition to natural, traditional mating, artificial insemination has gained popularity among goat breeders, as it allows easy access to a wide variety of bloodlines.

Gestation length is approximately 150 days. Twins are the usual result, with single and triplet births also common. Less frequent are litters of quadruplet, quintuplet, and even sextuplet kids. Birthing, known as kidding, generally occurs uneventfully. Just before kidding, the doe will have a sunken area around the tail and hip, as well as heavy breathing. She may have a worried look, become restless and display great affection for her keeper. The mother often eats the placenta, which gives her much-needed nutrients, helps stanch her bleeding, and parallels the behavior of wild herbivores, such as deer, to reduce the lure of the birth scent for predators.

Freshening (coming into milk production) occurs at kidding. Milk production varies with the breed, age, quality, and diet of the doe; dairy goats generally produce between of milk per 305-day lactation. On average, a good quality dairy doe will give at least of milk per day while she is in milk. A first-time milker may produce less, or as much as, or more of milk in exceptional cases. After the lactation, the doe will "dry off", typically after she has been bred. Occasionally, goats that have not been bred and are continuously milked will continue lactation beyond the typical 305 days. Meat, fiber, and pet breeds are not usually milked and simply produce enough for the kids until weaning.

Male lactation is also known to occur in goats.

Goats are reputed to be willing to eat almost anything, including tin cans and cardboard boxes. While goats will not actually eat inedible material, they are browsing animals, not grazers like cattle and sheep, and (coupled with their highly curious nature) will chew on and taste just about anything remotely resembling plant matter to decide whether it is good to eat, including cardboard, clothing and paper (such as labels from tin cans). The unusual smells of leftover food in discarded cans or boxes may further stimulate their curiosity.

Goats prefer to browse on vines, such as kudzu, on shrubbery and on weeds, more like deer than sheep, preferring them to grasses. Nightshade is poisonous; wilted fruit tree leaves can also kill goats. Silage (fermented corn stalks) and haylage (fermented grass hay) can be used if consumed immediately after opening – goats are particularly sensitive to "Listeria" bacteria that can grow in fermented feeds. Alfalfa, a high-protein plant, is widely fed as hay; fescue is the least palatable and least nutritious hay. Mold in a goat's feed can make it sick and possibly kill it.

In various places in China, goats are used in the production of tea. Goats are released onto the tea terraces where they avoid consuming the green tea leaves (which contain bitter tasting substances) but instead eat the weeds. The goats' droppings fertilise the tea plants.

The digestive physiology of a very young kid (like the young of other ruminants) is essentially the same as that of a monogastric animal. Milk digestion begins in the abomasum, the milk having bypassed the rumen via closure of the reticuloesophageal groove during suckling. At birth, the rumen is undeveloped, but as the kid begins to consume solid feed, the rumen soon increases in size and in its capacity to absorb nutrients.

The adult size of a particular goat is a product of its breed (genetic potential) and its diet while growing (nutritional potential). As with all livestock, increased protein diets (10 to 14%) and sufficient calories during the prepuberty period yield higher growth rates and larger eventual size than lower protein rates and limited calories. Large-framed goats, with a greater skeletal size, reach mature weight at a later age (36 to 42 months) than small-framed goats (18 to 24 months) if both are fed to their full potential. Large-framed goats need more calories than small-framed goats for maintenance of daily functions.

Goats are naturally curious. They are also agile and well known for their ability to climb and balance in precarious places. This makes them the only ruminant to regularly climb trees. Due to their agility and inquisitiveness, they are notorious for escaping their pens by testing fences and enclosures, either intentionally or simply because they are used to climbing. If any of the fencing can be overcome, goats will almost inevitably escape. Due to their intelligence, once a goat has discovered a weakness in the fence, they will exploit it repeatedly, and other goats will observe and quickly learn the same method.

Goats explore anything new or unfamiliar in their surroundings, primarily with their prehensile upper lip and tongue, by nibbling at them, occasionally even eating them.

When handled as a group, goats tend to display less herding behavior than sheep. When grazing undisturbed, they tend to spread across the field or range, rather than feed side-by-side as do sheep. When nursing young, goats will leave their kids separated ("lying out") rather than clumped, as do sheep. They will generally turn and face an intruder and bucks are more likely to charge or butt at humans than are rams.

While goats are generally considered hardy animals and in many situations receive little medical care, they are subject to a number of diseases. Among the conditions affecting goats are respiratory diseases including pneumonia, foot rot, internal parasites, pregnancy toxosis and feed toxicity. Feed toxicity can vary based on breed and location. Certain foreign fruits and vegetables can be toxic to different breeds of goats.

Goats can become infected with various viral and bacterial diseases, such as foot-and-mouth disease, caprine arthritis encephalitis, caseous lymphadenitis, pinkeye, mastitis, and pseudorabies. They can transmit a number of zoonotic diseases to people, such as tuberculosis, brucellosis, Q-fever, and rabies.

Life expectancy for goats is between fifteen and eighteen years. An instance of a goat reaching the age of 24 has been reported.

Several factors can reduce this average expectancy; problems during kidding can lower a doe's expected life span to ten or eleven, and stresses of going into rut can lower a buck's expected life span to eight to ten years.

A goat is useful to humans when it is living and when it is dead, first as a renewable provider of milk, manure, and fiber, and then as meat and hide. Some charities provide goats to impoverished people in poor countries, because goats are easier and cheaper to manage than cattle, and have multiple uses. In addition, goats are used for driving and packing purposes.

The intestine of goats is used to make "catgut", which is still in use as a material for internal human surgical sutures and strings for musical instruments. The horn of the goat, which signifies plenty and wellbeing (the cornucopia), is also used to make spoons.

According to the Food and Agriculture Organization (FAO), the top producers of goat milk in 2008 were India (4 million metric tons), Bangladesh (2.16 million metric tons) and the Sudan (1.47 million metric tons).

Husbandry, or animal care and use, varies by region and culture. The particular housing used for goats depends not only on the intended use of the goat, but also on the region of the world where they are raised. Historically, domestic goats were generally kept in herds that wandered on hills or other grazing areas, often tended by goatherds who were frequently children or adolescents, similar to the more widely known shepherd. These methods of herding are still used today.

In some parts of the world, especially Europe and North America, distinct breeds of goats are kept for dairy (milk) and for meat production. Excess male kids of dairy breeds are typically slaughtered for meat. Both does and bucks of meat breeds may be slaughtered for meat, as well as older animals of any breed. The meat of older bucks (more than one year old) is generally considered not desirable for meat for human consumption. Castration at a young age prevents the development of typical buck odor.
Dairy goats are generally pastured in summer and may be stabled during the winter. As dairy does are milked daily, they are generally kept close to the milking shed. Their grazing is typically supplemented with hay and concentrates. Stabled goats may be kept in stalls similar to horses, or in larger group pens. In the US system, does are generally rebred annually. In some European commercial dairy systems, the does are bred only twice, and are milked continuously for several years after the second kidding.

Meat goats are more frequently pastured year-round, and may be kept many miles from barns. Angora and other fiber breeds are also kept on pasture or range. Range-kept and pastured goats may be supplemented with hay or concentrates, most frequently during the winter or dry seasons.

In the Indian subcontinent and much of Asia, goats are kept largely for milk production, both in commercial and household settings. The goats in this area may be kept closely housed or may be allowed to range for fodder. The Salem Black goat is herded to pasture in fields and along roads during the day, but is kept penned at night for safe-keeping.

In Africa and the Mideast, goats are typically run in flocks with sheep. This maximizes the production per acre, as goats and sheep prefer different food plants. Multiple types of goat-raising are found in Ethiopia, where four main types have been identified: pastured in annual crop systems, in perennial crop systems, with cattle, and in arid areas, under pastoral (nomadic) herding systems. In all four systems, however, goats were typically kept in extensive systems, with few purchased inputs. Household goats are traditionally kept in Nigeria. While many goats are allowed to wander the homestead or village, others are kept penned and fed in what is called a 'cut-and-carry' system. This type of husbandry is also used in parts of Latin America. Cut-and-carry, which refers to the practice of cutting down grasses, corn or cane for feed rather than allowing the animal access to the field, is particularly suited for types of feed, such as corn or cane, that are easily destroyed by trampling.

Pet goats may be found in many parts of the world when a family keeps one or more animals for emotional reasons rather than as production animals. It is becoming more common for goats to be kept exclusively as pets in North America and Europe.

The taste of goat kid meat is similar to that of spring lamb meat; in fact, in the English-speaking islands of the Caribbean, and in some parts of Asia, particularly Bangladesh, Pakistan and India, the word “mutton” is used to describe both goat and lamb meat. However, some compare the taste of goat meat to veal or venison, depending on the age and condition of the goat. Its flavor is said to be primarily linked to the presence of 4-methyloctanoic and 4-methylnonanoic acid. It can be prepared in a variety of ways, including stewing, baking, grilling, barbecuing, canning, and frying; it can be minced, curried, or made into sausage. Due to its low fat content, the meat can toughen at high temperatures if cooked without additional moisture. One of the most popular goats grown for meat is the South African Boer, introduced into the United States in the early 1990s. The New Zealand Kiko is also considered a meat breed, as is the myotonic or "fainting goat", a breed originating in Tennessee.

Goats produce about 2% of the world's total annual milk supply. Some goats are bred specifically for milk. If the strong-smelling buck is not separated from the does, his scent will affect the milk.

Goat milk naturally has small, well-emulsified fat globules, which means the cream remains suspended in the milk, instead of rising to the top, as in raw cow milk; therefore, it does not need to be homogenized. Indeed, if the milk is to be used to make cheese, homogenization is not recommended, as this changes the structure of the milk, affecting the culture's ability to coagulate the milk and the final quality and yield of cheese.

Dairy goats in their prime (generally around the third or fourth lactation cycle) average——of milk production daily—roughly —during a ten-month lactation, producing more just after freshening and gradually dropping in production toward the end of their lactation. The milk generally averages 3.5% butterfat.

Goat milk is commonly processed into cheese, butter, ice cream, yogurt, "cajeta" and other products. Goat cheese is known as "fromage de chèvre" ("goat cheese") in France. Some varieties include Rocamadour and Montrachet. Goat butter is white because goats produce milk with the yellow beta-carotene converted to a colorless form of vitamin A.

The American Academy of Pediatrics discourages feeding infants milk derived from goats. An April 2010 case report summarizes their recommendation and presents "a comprehensive review of the consequences associated with this dangerous practice", also stating, "Many infants are exclusively fed unmodified goat's milk as a result of cultural beliefs as well as exposure to false online information. Anecdotal reports have described a host of morbidities associated with that practice, including severe electrolyte abnormalities, metabolic acidosis, megaloblastic anemia, allergic reactions including life-threatening anaphylactic shock, hemolytic uremic syndrome, and infections." Untreated caprine brucellosis results in a 2% case fatality rate. According to the USDA, doe milk is not recommended for human infants because it contains "inadequate quantities of iron, folate, vitamins C and D, thiamine, niacin, vitamin B, and pantothenic acid to meet an infant’s nutritional needs" and may cause harm to an infant's kidneys and could cause metabolic damage.

The department of health in the United Kingdom has repeatedly released statements stating on various occasions that "Goats' milk is not suitable for babies, and infant formulas and follow-on formulas based on goats' milk protein have not been approved for use in Europe", and "infant milks based on goats' milk protein are not suitable as a source of nutrition for infants." Moreover, according to the Canadian federal health department "Health Canada", most of the dangers of, and counter-indications for, feeding unmodified goat's milk to infants parallel those associated with unmodified cow's milk — especially insofar as allergic reactions go.

However, some farming groups promote the practice. For example, Small Farm Today, in 2005, claimed beneficial use in invalid and convalescent diets, proposing that glycerol ethers, possibly important in nutrition for nursing infants, are much higher in does' milk than in cows' milk. A 1970 book on animal breeding claimed that does' milk differs from cows' or humans' milk by having higher digestibility, distinct alkalinity, higher buffering capacity, and certain therapeutic values in human medicine and nutrition. George Mateljan suggested doe milk can replace ewe milk or cow milk in diets of those who are allergic to certain mammals' milk. However, like cow milk, doe milk has lactose (sugar), and may cause gastrointestinal problems for individuals with lactose intolerance. In fact, the level of lactose is similar to that of cow milk.

These compositions vary by breed (especially in the Nigerian dwarf breed), animal, and point in the lactation period.

The Angora breed of goats produces long, curling, lustrous locks of mohair. The entire body of the goat is covered with mohair and there are no guard hairs. The locks constantly grow to four inches or more in length. Angora crossbreeds, such as the pygora and the nigora, have been created to produce mohair and/or cashgora on a smaller, easier-to-manage animal.
The wool is shorn twice a year, with an average yield of about.

Most goats have softer insulating hairs nearer the skin, and longer guard hairs on the surface. The desirable fiber for the textile industry is the former, and it goes by several names (down, cashmere and pashmina). The coarse guard hairs are of little value as they are too coarse, difficult to spin and difficult to dye. The cashmere goat produces a commercial quantity of cashmere wool, which is one of the most expensive natural fibers commercially produced; cashmere is very fine and soft. The cashmere goat fiber is harvested once a year, yielding around of down.

In South Asia, cashmere is called "pashmina" (from Persian "pashmina", "fine wool").
In the 18th and early 19th centuries, Kashmir (then called Cashmere by the British), had a thriving industry producing shawls from goat-hair imported from Tibet and Tartary through Ladakh. The shawls were introduced into Western Europe when the General in Chief of the French campaign in Egypt (1799–1802) sent one to Paris. Since these shawls were produced in the upper Kashmir and Ladakh region, the wool came to be known as "cashmere".

Goats have been used by humans to clear unwanted vegetation for centuries. They have been described as "eating machines" and "biological control agents". There has been a resurgence of this in North America since 1990, when herds were used to clear dry brush from California hillsides thought to be endangered by potential wildfires. This form of using goats to clear land is sometimes known as conservation grazing. Since then, numerous public and private agencies have hired private herds to perform similar tasks. This practice has become popular in the Pacific Northwest, where they are used to remove invasive species not easily removed by humans, including (thorned) blackberry vines and poison oak.

As a goat's anatomy and physiology is not too dissimilar from that of human, some countries' militaries use goats to train combat medics. In the United States, goats have become the main animal species used for this purpose after Pentagon phased out using dogs for medical training in the 1980s. While modern mannequins used in medical training are quite efficient in simulating the behavior of a human body, trainees feel that "the goat exercise provide[s] a sense of urgency that only real life trauma can provide".

Some people choose goats as a pet because of their ability to form close bonds with their human guardians. Because of goats' herd mentality, they will follow their owners around and form close bonds with them.

Goat breeds fall into overlapping, general categories. They are generally distributed in those used for dairy, fiber, meat, skins, and as companion animals. Some breeds are also particularly noted as pack goats.

Goat breeders' clubs frequently hold shows, where goats are judged on traits relating to conformation, udder quality, evidence of high production, longevity, build and muscling (meat goats and pet goats) and fiber production and the fiber itself (fiber goats). People who show their goats usually keep registered stock and the offspring of award-winning animals command a higher price. Registered goats, in general, are usually higher-priced if for no other reason than that records have been kept proving their ancestry and the production and other data of their sires, dams, and other ancestors. A registered doe is usually less of a gamble than buying a doe at random (as at an auction or sale barn) because of these records and the reputation of the breeder.
Children's clubs such as 4-H also allow goats to be shown. Children's shows often include a showmanship class, where the cleanliness and presentation of both the animal and the exhibitor as well as the handler's ability and skill in handling the goat are scored. In a showmanship class, conformation is irrelevant since this is not what is being judged.

Various "Dairy Goat Scorecards" (milking does) are systems used for judging shows in the US. The American Dairy Goat Association (ADGA) scorecard for an adult doe includes a point system of a hundred total with major categories that include general appearance, the dairy character of a doe (physical traits that aid and increase milk production), body capacity, and specifically for the mammary system. Young stock and bucks are judged by different scorecards which place more emphasis on the other three categories; general appearance, body capacity, and dairy character.

The American Goat Society (AGS) has a similar, but not identical scorecard that is used in their shows. The miniature dairy goats may be judged by either of the two scorecards. The "Angora Goat scorecard" used by the Colored Angora Goat Breeder's Association (CAGBA), which covers the white and the colored goats, includes evaluation of an animal's fleece color, density, uniformity, fineness, and general body confirmation. Disqualifications include: a deformed mouth, broken down pasterns, deformed feet, crooked legs, abnormalities of testicles, missing testicles, more than 3 inch split in scrotum, and close-set or distorted horns.

Archaeologists excavating the ancient city of Ebla in Syria discovered, among others, the tomb of some king or great noble which included
a throne decorated with bronze goat heads. That led to this tomb becoming known as "The Tomb of the Lord of the Goats".
According to Norse mythology, the god of thunder, Thor, has a chariot that is pulled by the goats Tanngrisnir and Tanngnjóstr. At night when he sets up camp, Thor eats the meat of the goats, but takes care that all bones remain whole. Then he wraps the remains up, and in the morning, the goats always come back to life to pull the chariot. When a farmer's son who is invited to share the meal breaks one of the goats' leg bones to suck the marrow, the animal's leg remains broken in the morning, and the boy is forced to serve Thor as a servant to compensate for the damage.

Possibly related, the Yule Goat is one of the oldest Scandinavian and Northern European Yule and Christmas symbols and traditions. Yule Goat originally denoted the goat that was slaughtered around Yule, but it may also indicate a goat figure made out of straw. It is also used about the custom of going door-to-door singing carols and getting food and drinks in return, often fruit, cakes and sweets. "Going Yule Goat" is similar to the British custom wassailing, both with roots. The Gävle Goat is a giant version of the Yule Goat, erected every year in the Swedish city of Gävle.

The Greek god Pan is said to have the upper body of a man and the horns and lower body of a goat. Pan was a very lustful god, nearly all of the myths involving him had to do with him chasing nymphs. He is also credited with creating the pan flute.

The goat is one of the twelve-year cycle of animals which appear in the Chinese zodiac related to the Chinese calendar. Each animal is associated with certain personality traits; those born in a year of the goat are predicted to be shy, introverted, creative, and perfectionist.

Several mythological hybrid creatures are believed to consist of parts of the goat, including the Chimera. The Capricorn sign in the Western zodiac is usually depicted as a goat with a fish's tail. Fauns and satyrs are mythological creatures that are part goat and part human. The mineral bromine is named from the Greek word "brόmos", which means "stench of he-goats".

Goats are mentioned many times in the Bible. A goat is considered a "clean" animal by Jewish dietary laws and was slaughtered for an honored guest. It was also acceptable for some kinds of sacrifices. Goat-hair curtains were used in the tent that contained the tabernacle (Exodus 25:4). Its horns can be used instead of sheep's horn to make a shofar. On Yom Kippur, the festival of the Day of Atonement, two goats were chosen and lots were drawn for them. One was sacrificed and the other allowed to escape into the wilderness, symbolically carrying with it the sins of the community. From this comes the word "scapegoat". A leader or king was sometimes compared to a male goat leading the flock. In the New Testament, Jesus told a parable of the Sheep and the Goats (Gospel of Matthew 25).

Popular Christian folk tradition in Europe associated Satan with imagery of goats. A common superstition in the Middle Ages was that goats whispered lewd sentences in the ears of the saints. The origin of this belief was probably the behavior of the buck in rut, the very epitome of lust. The common medieval depiction of the Devil was that of a goat-like face with horns and small beard (a goatee). The Black Mass, a probably mythological "Satanic mass", involved Satan manifesting as a black goat for worship.

The goat has had a lingering connection with Satanism and pagan religions, even into modern times. The inverted pentagram, a symbol used in Satanism, is said to be shaped like a goat's head. The "Baphomet of Mendes" refers to a satanic goat-like figure from 19th-century occultism.

The common Russian surname "Kozlov" (), means "goat". Goatee refers to a style of facial hair incorporating hair on a man's chin, so named because of some similarity to a goat's facial feature.

Goats readily revert to the wild (become feral) if given the opportunity. The only domestic animal known to return to feral life as swiftly is the cat. Feral goats have established themselves in many areas: they occur in Australia, New Zealand, Great Britain, the Galapagos and in many other places. When feral goats reach large populations in habitats which provide unlimited water supply and which do not contain sufficient large predators or which are otherwise vulnerable to goats' aggressive grazing habits, they may have serious effects, such as removing native scrub, trees and other vegetation which is required by a wide range of other creatures, not just other grazing or browsing animals. Feral goats are common in Australia. However, in other circumstances where predator pressure is maintained, they may be accommodated into some balance in the local food web.