Domestication (from Latin domesticus) is the process whereby a population of animals or plants, through a process of artificial selection, is changed at the genetic level, accentuating traits desired by humans. It differs from taming in that a change in the phenotypical expression and genotype of the animal occurs, where as taming is simply the process where animals become acclimatized to human presence. In the Convention on Biological Diversity a domesticated species is defined as a 'species in which the evolutionary process has been influenced by humans to meet their needs'.[1] Therefore, a defining characteristic of domestication is artificial selection by humans. Humans have brought these populations under their control and care for a wide range of reasons: to produce food or valuable commodities (such as wool, cotton, or silk), for help with various types of work (such as transportation, protection, and warfare), scientific research, or simply to enjoy as companions or ornaments.
Plants domesticated primarily for aesthetic enjoyment in and around the home are usually called house plants or ornamentals, while those domesticated for large-scale food production are generally called crops. A distinction can be made between those domesticated plants that have been deliberately altered or selected for special desirable characteristics (see cultigen) and those domesticated plants that are essentially no different from their wild counterparts (assuming domestication does not necessarily imply physical modification). Animals domesticated for home companionship are usually called pets while those domesticated for food or work are called livestock or farm animals.
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Charles Darwin described how the process of domestication can involve both unconscious and methodical elements. Routine human interactions with animals and plants create selection pressures that cause adaptation as species adjust to human presence, use or cultivation. Deliberate selective breeding has also been used to create desired changes, often after initial domestication. These two forces, unconscious natural selection and methodical selective breeding, may have both played roles in the processes of domestication throughout history.[2] Both have been described from man's perspective as processes of artificial selection.
The domestication of wheat provides an example. Wild wheat falls to the ground to reseed itself when ripe, but domesticated wheat stays on the stem for easier harvesting. There is evidence that this critical change came about as a result of a random mutation near the beginning of wheat's cultivation. Wheat with this mutation was harvested and became the seed for the next crop. Therefore, without realizing, early farmers selected for this mutation, which would otherwise have died out. The result is domesticated wheat, which relies on farmers for its own reproduction and dissemination.[3]
Mutation is not the only way in which natural and artificial selection operate. Darwin describes how natural variations in individual plants and animals also support the selection of new traits. It is speculated that tamer than average wolves, less wary of humans, selected themselves as domestic dogs over many generations. These wolves were able to thrive by following humans to scavenge for food near camp fires and garbage dumps. Eventually a symbiotic relationship developed between people and these proto-dogs. The dogs fed on human food scraps, and humans found that dogs could warn them of approaching dangers, help with hunting, act as pets, provide warmth, or supplement their food supply. As this relationship , humans eventually began to keep these self-tamed wolves and breed from them the types of dogs that we have today.
In recent times, selective breeding may best explain how continuing processes of domestication often work. Some of the best-known evidence of the power of selective breeding comes from an experiment by Russian scientist, Dmitri K. Belyaev, in the 1950s. His team spent many years breeding the Silver Fox (Vulpes vulpes) and selecting only those individuals that showed the least fear of humans. Eventually, Belyaev's team selected only those that showed the most positive response to humans. He ended up with a population of grey-coloured foxes whose behavior and appearance was significantly changed. They no longer showed any fear of humans and often wagged their tails and licked their human caretakers to show affection. Fascinatingly, these foxes had floppy ears, smaller skulls, rolled tails and other traits commonly found in dogs.[4]
Despite the success of this experiment, it appears that selective breeding cannot always achieve domestication. Attempts to domesticate many kinds of wild animals have been unsuccessful. The zebra is one example. Despite the fact that four species of zebra can interbreed with and are part of the same genus as the horse and the donkey, attempts at domestication have failed.[5] The factors which influence 'domesticatability' of large animals (see below) are discussed in some detail in Jared Diamond's Guns, Germs, and Steel (1999).[2] Surprisingly, in human history to date, only a few species of large animal have been domesticated. In approximate order of their earliest domestication these are: dog, sheep, goat, pig, cow, horse, donkey, water buffalo, llama, alpaca, bactrian camel, Arabian camel, yak, reindeer, and elephant.
According to evolutionary biologist Jared Diamond, animal species must meet six criteria in order to be considered for domestication:[6]
However, this list is of limited use because it fails to take into account the profound changes that domestication has on a species. While it is true that some animals, including parrots, whales, and most members of the Carnivora, retain their wild instincts even if born in captivity, some factors must be taken into consideration. In particular, number (5) may not be a prerequisite for domestication, but rather a natural consequence of a species' having been domesticated. In other words, wild animals are naturally timid and flighty because they are constantly faced by predators; domestic animals do not need such a nervous disposition, because they are protected by their human owners. The same holds true for number (4)—aggressive temperament is an adaptation to the danger from predators. A Cape buffalo can kill even an attacking lion. Number (6), while it does apply to most domesticated species, also has exceptions, most notably in the domestic cat and ferret, which are both descended from strictly solitary wild ancestors but which tolerate and even seek out social interaction in their domestic forms. Feral domestic cats, for example, naturally form colonies around concentrated food sources and will even share prey and rear kittens communally, while wildcats remain solitary even in the presence of such food sources.[7] Zoologist Marston Bates devoted a chapter on domestication in his 1960 book The Forest and the Sea, in which he talks a great deal about how domestication alters a species: Dispersal mechanisms tend to disappear for the reason stated above, and also because people provide transportation for them. Chickens have practically lost their ability to fly. Similarly, domestic animals cease to have a definite mating season, and so the need to be territorial when mating loses its value. What he says suggests that the process of domestication can itself make a creature domesticable. Besides, the first steps towards agriculture may have involved hunters keeping young animals, who are always more impressionable than the adults, after killing their mothers.
The earliest human attempts at plant domestication occurred in South-Western Asia. 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 BP) contexts at Abu Hureyra in Syria,[8] 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 BC 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 BC, most likely due to the migration of peoples from Asia to America.[9]
Cereal crops were first domesticated around 9000 BC 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 trial and error that occurred intermittently. Over time perennials and small trees began to be domesticated including apples and olives. Some plants were not domesticated until recently such as the macadamia nut and the pecan.
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.
Over the millennia many domesticated species have become utterly unlike their natural ancestors. Maize ears are now dozens of times the size of those of wild teosinte. A similar change occurred between wild strawberries and domesticated strawberries.
Domesticated plant species often differ from their wild relatives in predictable ways. These differences are called the domestication syndrome, and include:[10]
Lad
Due to elephants' slow growth, the boundaries between surviving wild populations and domestic clades can be vague. Similar problems of definition arise when domesticated cats go feral. A classification system that can help solve this confusion surrounding animal populations might be set up on a spectrum of increasing domestication:
This classification system does not account for several complicating factors: genetically modified organisms, feral populations, and hybridization. Many species that are farmed or ranched are now being genetically modified. This creates a unique category because it alters the organisms as a group but in ways unlike traditional domestication. Feral organisms are members of a population that was once raised under human control, but is now living and multiplying outside of human control. Examples include mustangs. Hybrids can be wild, domesticated, or both: a liger is a hybrid of two wild animals, a mule is a hybrid of two domesticated animals, and a beefalo is a cross between a wild and a domestic animal.
A great difference exists between a tame animal and a domesticated animal. The term "domesticated" refers to an entire species or variety while the term "tame" can refer to just one individual within a species or variety. Humans have tamed many thousands of animals that have never been truly domesticated. These include the elephant, giraffes, and bears. There is debate over whether some species have been domesticated or just tamed. Some state that the elephant has been domesticated, while others argue the cat has never been. Dividing lines include whether a specimen born to wild parents would differ in appearance or behavior from one born to domesticated parents. For instance a dog is certainly domesticated because even a wolf (genetically the origin of all dogs) raised from a pup would be very different from a dog, in both appearance and behaviour.[11]
Selection of animals for visible “desirable” traits may make them unfit in other, unseen, ways. The consequences for the captive and domesticated animals were reduction in 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 a few of the defects of domestic animals, All of these changes have been documented in direct observations of the rat in the 19th century, by archaeological evidence, and confirmed by animal breeders in the 20th century.[12]
One 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. Humans share over sixty diseases with dogs . Many parasites also have their origins in domestic animals.[2] 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.
Since the process of domestication inherently takes many generations over a long period of time, and the spread of breed and husbandry techniques is also slow, it is not meaningful to give a single "date of domestication". However, it is believed that the first attempt at domestication of both animals and plants were made in the Old World by peoples of the Mesolithic Period. The tribes that took part in hunting and gathering wild edible plants, started to make attempts to domesticate dogs, goats, and possibly sheep, which was as early as 9000 BC. However, it was not until the Neolithic Period that primitive agriculture appeared as a form of social activity, and domestication was well under way. The great majority of domesticated animals and plants that still serve humans were selected and developed during the Neolithic Period, a few other examples appeared later. The rabbit for example, was not domesticated until the Middle Ages, while the sugar beet came under cultivation as a sugar-yielding agricultural plant in the 19th century. As recently as the 20th century, mint became an object of agricultural production, and animal breeding programs to produce high-quality fur were started in the same time period.[13]
The methods available to estimate domestication dates introduce further uncertainty, especially when domestication has occurred in the distant past. So the dates given here should be treated with caution; in some cases evidence is scanty and future discoveries may alter the dating significantly.
Dates and places of domestication are mainly estimated by archaeological methods, more precisely archaeozoology. These methods consist of excavating or studying the results of excavation in human prehistorical occupation sites. Animal remains are dated with archaeological methods, the species they belong to is determined, the age at death is also estimated, and if possible the form they had, that is to say a possible domestic form. Various other clues are taken advantage of, such as slaughter or cutting marks. The aim is to determine if they are game or raised animal, and more globally the nature of their relationship with humans. For example the skeleton of a cat found buried close to humans is a clue that it may have been a pet cat. The age structure of animal remains can also be a clue of husbandry, in which animals were killed at the optimal age.
New technologies and especially mitochondrial DNA, which are simple DNA found in the mitochondria that determine its function in the cell provide an alternative angle of investigation, and make it possible to reestimate the dates of domestication based on research into the genealogical tree of modern domestic animals.
It is admitted for several species that domestication occurred in several places distinctly. For example, research on mitochondrial DNA of the modern cattle Bos taurus supports the archaeological assertions of separate domestication events in Asia and Africa. This research also shows that Bos taurus and Bos indicus haplotypes are all descendants of the extinct wild ox Bos primigenius.[14][15] However, this does not rule out later crossing inside a species; therefore it appears useless to look for a separate wild ancestor for each domestic breed.
The first animal to be domesticated appears to have been the dog, in the Upper Paleolithic era. This preceded the domestication of other species by several millennia. In the Neolithic a number of important species such as the goat, sheep, pig and cow were domesticated, as part of the spread of farming with characterises this period. The goat, sheep and pig in particular were domesticated independently in the Levant and Asia.
There is early evidence of beekeeping, in the form of rock paintings, dating to 13,000 BC.
Recent archaeological evidence from Cyprus indicates domestication of a type of cat by perhaps 9500 BC.[16][17][18]
The earliest secure evidence of horse domestication, bit wear on horse molars at Dereivka in Ukraine, dates to around 4000 BC. The unequivocal date of domestication and use as a means of transport is at the Sintashta chariot burials in the southern Urals, c. 2000 BC. Local equivalents and smaller species were domesticated from the 2500s BC.
The availability of both domesticated vegetable and animal species increased suddenly following the voyages of Christopher Columbus and the contact between the Eastern and Western Hemispheres. This is part of what is referred to as the Columbian Exchange.
| Species | Date | Location |
|---|---|---|
| Dog (Canis lupus familiaris) | between 30000 BC and 7000 BC[19][20][21] | East Asia and Africa |
| Sheep (Ovis orientalis aries) | between 11000 BC and 9000 BC[22][23] | Southwest Asia |
| Pig (Sus scrofa domestica) | 9000 BC[24][25] | Near East, China, Germany |
| Goat (Capra aegagrus hircus) | 8000 BC[26] | Iran |
| Cow (Bos primigenius taurus) | 8000 BC[27][28] | India, Middle East, and North Africa |
| Cat (Felis catus) | 7500 BC[16][17][18][29] | Cyprus and Near East |
| Chicken (Gallus gallus domesticus) | 6000 BC[30] | India and Southeast Asia |
| Guinea pig (Cavia porcellus) | 5000 BC[31] | Peru |
| Donkey (Equus africanus asinus) | 5000 BC[32][33] | Egypt |
| Domesticated duck (Anas platyrhynchos domesticus) | 4000 BC | China |
| Water buffalo (Bubalus bubalis) | 4000 BC | India, China |
| Horse (Equus ferus caballus) | 4000 BC[34] | Eurasian Steppes |
| Dromedary (Camelus dromedarius) | 4000 BC | Arabia |
| Llama (Lama glama) | 3500 BC | Peru |
| Silkworm (Bombyx mori) | 3000 BC | China |
| Reindeer (Rangifer tarandus) | 3000 BC[35] | Russia |
| Rock pigeon (Columba livia) | 3000 BC | Mediterranean Basin |
| Goose (Anser anser domesticus) | 3000 BC[36] | Egypt |
| Bactrian camel (Camelus bactrianus) | 2500 BC | Central Asia |
| Yak (Bos grunniens) | 2500 BC | Tibet |
| Banteng (Bos javanicus) | Unknown | Southeast Asia, Java Island |
| Gayal (Bos gaurus frontalis) | Unknown | Southeast Asia |
| Alpaca (Vicugna pacos) | 1500 BC | Peru |
| Ferret (Mustela putorius furo) | 1500 BC- | Europe |
| Muscovy Duck (Cairina momelanotus) | Unknown | South America |
| Guineafowl | Unknown | Africa |
| Common carp | Unknown | East Asia |
| Domesticated turkey | 500 BC | Mexico |
| Goldfish | Unknown | China |
| European Rabbit | AD 600 | Europe |
Second circle
| Species | Date | Location |
|---|---|---|
| Zebu (Bos primigenius indicus) | 8000 BC | India |
| Honey bee | 4000 BC | Multiple places |
| Asian Elephant | 2000 BC(Possibly Endangered | Indus Valley civilization |
| Fallow Deer | 1000 BC | Mediterranean Basin |
| Indian Peafowl | 500 BC | India |
| Barbary Dove | 500 BC | North Africa |
| Japanese Quail (see Quail) | 1100–1900 | Japan |
| Mandarin Duck | Unknown | China |
| Mute Swan | 1000–1500 | Europe |
| Canary (Serinus canaria domestica) | 1600 | Canary Islands, Europe |
| Species | Date | Location |
|---|---|---|
| Fancy rat | 1800s | UK |
| Fox | 1800s | Europe |
| Mink | 1800s | Europe |
| Budgerigar | 1850s | Europe |
| Cockatiel | 1870s | Europe |
| Zebra Finch | 1900s | Australia |
| Hamster | 1930s | United States |
| Silver Fox | 1950s | Soviet Union |
| Muskox | 1960s | United States |
| Corn Snake | 1960s | United States |
| Ball python | 1960s | |
| Madagascar hissing cockroach | 1960s | |
| Red Deer | 1970s | New Zealand |
| Hedgehog | 1980s | United States |
| Sugar Glider | 1980s | Australia |
| Skunk | 1980s | United States |
| Kinkajou | date uncertain | Central America |
A project is underway to find the genetic basis for taming. Researchers at the Max Planck institute in Germany have obtained two sets of rats bred in Russia. One set was selected for aggressiveness and another for tameness, mimicking the process by which neolithic farmers first domesticated animals.[37]
Some species are said to have been domesticated, but are not any more, either because they have totally disappeared, or since their domestic form no longer exists. Examples include the Jaguarundi,[38] the Kakapo, the Ring-tailed Cat, Cheetah, Caracal and Bos aegyptiacus.
Animals of domestic origin and feral ones sometimes can produce fertile hybrids with native, wild animals which leads to genetic pollution in the naturally evolved wild gene pools, many times threatening rare species with extinction. Cases include the mallard duck, wildcat, wild boar, the rock dove or pigeon, the Red Junglefowl (Gallus gallus) (ancestor of all chickens), carp, and more recently salmon. Another example is the dingo, itself an early feral dog, which hybridizes with dogs of European origin. On the other hand, genetic pollution seems not to be noticed for rabbits. There is much debate over the degree to which feral hybridization compromises the purity of a wild species. In the case of the mallard, for example, some claim there are no populations which are completely free of any domestic ancestor.
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