Domestication is a phenomenon whereby a wild biological organism is habituated to survive in the company of human beings
Domesticated animals, plants, and other organisms are those whose collective behavior, life cycle, or physiology has been altered as a result of their breeding and living conditions being under human control for multiple generations.
Domestication (from Latin domesticus) is the process whereby a population of animals or plants, through a process of selection, is changed at the genetic level, accentuating traits that benefit humans. It differs from taming in that a change in the phenotypical expression and genotype of the animal occurs, whereas taming is simply the process by which animals become accustomed 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." 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 ascompanions 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 plants that are used for human benefit, but are essentially no different from the wild populations of the species. Animals domesticated for home companionship are usually called pets while those domesticated for food or work are called livestock or farm animals.
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. Deliberateselective 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. 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'scultivation. 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.
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 asdomestic 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 progressed, 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. These foxes had floppy ears, smaller skulls, rolled tails and other traits commonly found in dogs.
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. The factors which influence 'domesticatability' of large animals (see below) are discussed in some detail in Jared Diamond's Guns, Germs, and Steel (1999). 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:
- Flexible diet — Creatures that are willing to consume a wide variety of food sources and can live off less cumulative food from the food pyramid (such as corn or wheat), particularly food that is not utilized by humans (such asgrass and forage) are less expensive to keep in captivity. Carnivores by definition feed primarily or only on animal tissue, which requires the expenditure of many animals, though they may exploit sources of meat not utilized by humans, such as scraps and vermin.
- Reasonably fast growth rate — Fast maturity rate compared to the human life span allows breeding intervention and makes the animal useful within an acceptable duration of caretaking. Large animals such as elephants require many years before they reach a useful size.
- Ability to be bred in captivity — Creatures that are reluctant to breed when kept in captivity do not produce useful offspring, and instead are limited to capture in their wild state. Creatures such as the panda, antelope and giant forest hog are territorial when breeding and cannot be maintained in crowded enclosures in captivity.
- Pleasant disposition — Large creatures that are aggressive toward humans are dangerous to keep in captivity. The African buffalo has an unpredictable nature and is highly dangerous to humans; similarly, although the American bison is raised in enclosed ranges in the US West, it is much too dangerous to be regarded as truly domesticated. Although similar to the domesticated pig in many ways, the American peccary and Africa's warthog and bushpigare also dangerous in captivity. However one must keep in mind that most (if not all) modern large domestic animals were descendants of extremely aggressive ancestors. The wild boar, ancestor of the domestic pig, is certainly renowned for its ferocity; other examples include the aurochs (ancestor of modern cattle), horse, Bactrian camels and yaks, all of which are no less dangerous than their undomesticated wild relatives such as zebras and buffalos. On the other hand for thousands of years humans have managed to tame dangerous species like the elephants, bears and cheetahs whose failed domestications had little to do with their aggressiveness.
- Temperament which makes it unlikely to panic — A creature with a nervous disposition is difficult to keep in captivity as it may attempt to flee whenever startled. The gazelle is very flighty and it has a powerful leap that allows it to escape an enclosed pen. Some animals, such as thedomestic sheep, still have a strong tendency to panic when their flight zone is encroached upon. However, most sheep also show a flocking instinct, whereby they stay close together when pressed. Livestock with such an instinct may be herded by people and dogs.
- Modifiable social hierarchy — Social creatures that recognize a hierarchy of dominance can be raised to recognize a human as the pack leader.
Another strong factor deciding whether a species will be considered for domestication is quite simply the availability of more suitable (or even better already domesticated) alternatives. For example a community that had been introduced to domestication by neighboring peoples will generally find it much more practical, economical and time saving to import already domesticated species than experiment with wild animals (even if they are of the same species).
The boundaries between surviving wild populations and domestic clades can be vague. A classification system that can help solve this confusion surrounding animal populations might be set up on a spectrum of increasing domestication:
- Wild: These populations experience their full life cycles without deliberate human intervention.
- Raised in Captivity/Captured from Wild (in zoos, botanical gardens, or for human gain): These populations are nurtured by humans but (except in zoos) not normally bred under human control. They remain as a group essentially indistinguishable in appearance or behaviour from their wild counterparts. Examples include Asian elephants, animals such as sloth bears and cobras used by showmen in India, and animals such as Asian black bears (farmed for their bile), and zoo animals, kept in captivity as examples of their species. (It should be noted that zoos and botanical gardens sometimes exhibit domesticated or feral animals and plants such as camels, mustangs, and some orchids.)
- Raised commercially (captive or semidomesticated): These populations are ranched or farmed in large numbers for food, commodities, or the pet trade, commonly breed in captivity, but as a group are not substantially altered in appearance or behavior from their wild cousins. Examples include the ostrich, various deer, alligator, cricket, pearl oyster, and ball python. (These species are sometimes referred to as partially domesticated.)
- Domesticated: These populations are bred and raised under human control for many generations and are substantially altered as a group in appearance or behaviour. Examples include pigs, ferrets, turkeys, canaries, domestic pigeons, budgerigars, goldfish, silkworms, dogs, cats,sheep, cattle, chickens, llamas, guinea pigs, laboratory mice, horses, goats and (silver) foxes.
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.Similar problems of definition arise when domesticated cats go feral.
List of domesticated animals