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 behaviours.
Commensal pathway site, Ukraine The dog is a classic example of a domestic animal that likely traveled a
commensal pathway into domestication. 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.
Migratory wolves theory 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 eat a large part of their quarry before other predators had detected the kill. One study proposed that during the Last Glacial Maximum, some humans teamed up with those pastoralist wolves and learned their techniques. Many early humans remained gatherers and scavengers, or specialized as fish-hunters, hunter-gatherers, and hunter-gardeners. However, some 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 remains of large carcasses left by human hunter-gatherers may have led some wolves into entering a migratory relationship with humans. This could have led to their divergence from those wolves that remained in the one territory. A closer relationship between these wolves – or proto-dogs – and humans may have then developed, such as hunting together and mutual defence from other carnivores and other humans. A maternal mDNA, paternal yDNA, 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 colouration divergence. A study has identified the remains of a population of extinct
Pleistocene Beringian wolves with unique mDNA 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.
Food partitioning theory Dogs were the only animal to be domesticated by mobile hunter-gatherers. Humans and wolves were both persistent pack hunters of large prey, were competing in overlapping territory, and are both capable of killing each other. One study proposes how humans may have domesticated such a dangerous competitor. Humans and wolves are members of the large carnivore guild, and when there is abundant game the top members leave carcasses for the other members to scavenge. When game is scarce there is often conflict. Humans are unusual members of this guild because they are
primates, therefore their ability to process meat is limited by the capacity of the liver to metabolize protein, and they can derive only 20% of their energy requirements from protein. High protein consumption in humans can lead to illness. During the harsh winters of the Last Glacial Maximum plant foods would have not been available, and meat would not be the favoured food but fat and grease would be, as is prized by some high-latitude dwelling peoples in modern times. Game meat would have been devoid of fat, but the limbs and crania contain fat deposits, and limb bones contain fatty oils. There is evidence of such processing during this period. Wolves are typical carnivores and can survive on a protein-based diet for months. Calculations of the lipid content of arctic and subarctic game available across the cold steppe environment at this time and today shows that in order to gain the necessary quantity of fat and oils, there would have been enough excess animal calories to feed either proto-dogs or wolves with no need for competition. Hunting together and protection from other predators would have been advantageous to both species, leading to domestication.
Genetic changes – grey wolf and chihuahua skulls (Italian mastiff) and a
Yorkshire terrier is over 30-fold, yet both are members of the same species.
The Yellow Dog Study Domestic dogs exhibit diverse
coat colours and patterns. In many mammals, different colour patterns are the result of the regulation of the
Agouti gene, which can cause hair follicles to switch from making black or brown pigments to yellow or nearly white pigments. The most common coat pattern found in modern wolves is
agouti, in which the upperside of the body has banded hairs and the underside exhibits lighter shading. The colour yellow is dominant to the colour black and is found in dogs across much of the world and the
dingo in Australia. In 2021, a study of whole genome sequences taken from dogs and wolves focused on the genetic relationships between them based on coat colour. The study found that most dog colour haplotypes were similar to most wolf haplotypes, however dominant yellow in dogs was closely related to white in arctic wolves from North America. This result suggests a common origin for dominant yellow in dogs and white in wolves but without recent gene flow, because this light colour clade was found to be basal to the golden jackal and genetically distinct from all other canids. The most recent common ancestor of the golden jackal and the wolf lineage dates back to 2 million YBP. The study proposes that 35,000 YBP there was genetic
introgression into the Late Pleistocene grey wolf from a
ghost population of an extinct canid which had diverged from the grey wolf lineage over 2 million YBP. This colour diversity could be found 35,000 YBP in wolves and 9,500 YBP in dogs. A closely related haplotype exists among those wolves of Tibet which possess yellow shading in their coats. The study explains the colour relationships between modern dogs and wolves, white wolves from North America, yellow dogs, and yellowish wolves from Tibet. The study concludes that during the Late Pleistocene, natural selection laid the genetic foundation for modern coat colour diversity in dogs and wolves.
Dietary adaptation Selection appears to have acted on the dog's metabolic functions to cope with changes in
dietary fat, followed later with a dietary increase in starch associated with a more commensal lifestyle. The dog
genome compared to the wolf genome shows signs of having undergone positive selection, these include genes relating to brain function and behaviour, 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 were left unused. :
See further: Dietary phenotypic plasticity Behaviour The key phase in domestication appears to have been changes in social behaviour and its corresponding
oxytocin receptor genes and
neural-related genes. Behaviour differences between dogs and wolves may be contributed by
structural variation in the genes that are associated with human
Williams-Beuren syndrome. This syndrome causes increased hyper-sociability, which may have been important during domestication. In 2014, a whole genome study of the DNA differences between wolves and dogs found that the dogs' tameness was not a reduced fear response but did show greater
synaptic plasticity. Synaptic plasticity is widely believed to be the cellular correlate of learning and memory. The study proposes that the improved learning and memory abilities of dogs also helped to lower their level of fear around humans. Unlike other domestic species which were primarily selected for production-related traits, dogs were initially selected for their behaviours. 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 behaviour 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 behavioural 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.
Role of epigenetics Differences in
hormonal expression that are associated with
domestication syndrome may be linked to
epigenetic modifications. A recent study that compared the
methylation patterns of dogs with those of wolves found 68 significantly different methylated sites. These included sites which are linked to two
neurotransmitter genes associated with
cognition. There is a direct association between the dog's social behaviour and
OXTR, which is a receptor for the neurotransmitter
oxytocin, and this has been caused through the epigenetic methylation of the OXTR gene. DNA methylation differences have been found between wolves and dogs, and between different dog breeds. This implies that epigenetic factors may have been important for both dog domestication and the divergence of dog breeds. Similar to humans, wolves show strong social and emotional bonds within their groupings, and this relationship might have been the foundation for the evolution of dog-human bonding. In 2019, a literature review led to a new theory named Active Social Domestication, in which the social environment of the dog ancestor induced
neuro-physiological changes that caused an epigenetic cascade, which led to the rapid development of domestication syndrome.
Dog and human coevolution Parallel evolution Being the first domesticated species by humans has created a strong bond between dogs and humans and entwined their histories. Dogs accompanied humans when they first migrated into new environments and show similar adaptations – such as to high altitude,
low oxygen conditions. There is an extensive list of
genes showing signatures of
parallel evolution in dogs and humans. This has led to the study of the
coevolution of gene function. 311 genes under positive selection in dogs are related to a large number of overlapping loci which show the same patterns in humans. These genes are involved in traits ranging from digestion and neurological processes to some cancers. For example, it has been inferred from genes which act on the
serotonergic system in the brain that coevolution has led to less aggressive behaviour when living in crowded environments. Dogs also suffer from many of the same common diseases as humans – including cancer, diabetes, heart disease, and neurological disorders. The underlying disease
pathologies are similar to those in humans, as are their responses to treatment and resultant outcomes.
Behavioural evidence Convergent evolution is when distantly related species independently evolve similar solutions to the same problem. For example, 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 behaviour. 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. Studies support coevolution in that dogs can follow the human pointing gesture, 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 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.
Human adoption of some wolf behaviours 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 behaviour would have been profound. 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 behaviours 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 behaviour 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. One might therefore argue that the closest approximation to human morality that can be found in nature is that of the grey wolf. 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 large 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. ==First dogs==