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Domestication, also called taming, is a practice whereby a wild biological organism is habituated to survive in the company of, or by the labor of, human beings. Domesticated animals, plants, and other organisms are those whose collective behaviour, life cycle, or physiology has been altered as a result of their breeding and living conditions under careful human control for multiple generations. Humans have brought these populations under their care for a wide range of reasons: for help with various types of work, to produce food or valuable commodities (such as wool, cotton, or silk), and to enjoy as pets or ornamental plants. 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. Likewise, animals domesticated for home companionship are usually called pets while those domesticated for food are called livestock or farm animals.
History of domestication
The earliest known domestic animal seems to probably have been the dog, likely as early as 15000 BC among hunter-gatherers in several locations. There is early evidence of beekeeping, in the form of rock paintings, dating to 13,000 BC. The next three - the goat, sheep and pig - were domesticated around 10-8000 BC, independently in the Levant and Asia. Recent archaeological evidence from Cyprus indicates domestication of a type of cat by perhaps 7500 BC. The earliest secure evidence of horse domestication, bit wear on horse molars at Dereivka in Ukraine, dates ca 4000BC. The unequivocal date of domestication and use as a means of transport is at the Sintashta chariot burials in the southern Urals, ca 2000 BC. Local equivalents and smaller species were domesticated from the 2500s BC.
The processes of domestication and the distribution of domesticated species were both radically affected by the establishment of regular contact between the Eastern and Western Hemispheres following the voyages of Christopher Columbus. This sudden increase in the transmission of organisms between the Eastern and Western Hemispheres is referred to as the Columbian Exchange.
|Approximate dates and locations of first domestication|
|Dog||15000 BCE||Multiple locations|
|Goat||10000 BCE||Asia and Middle East|
|Sheep||8000 BCE||Asia and Middle East|
|Cow||8000 BCE||India, Middle East, and Sub-sahara|
|Guinea pig||5000 BCE||Peru|
|Water buffalo||4000 BCE||China|
|Honeybee||4000 BCE||Southern Asia|
|Chicken||3500 BCE||Southeast Asia|
|Cat||3500 BCE to 7500 BC||Egypt or Cyprus|
|Bactrian camel||2500 BCE||Central Asia|
|Dromedary (Arabian camel)||2500 BCE||Arabia|
|Ferret||1500 BCE-500 BCE?||Europe?|
Obviously, these are not dates that are set in stone. In fact, these dates are possibly far from being accurate due to scanty evidence. The earliest estimates, however, are that animals started to be domesticated approximately 10,000 years ago (8000 B.C).
Process of domestication
There is debate within the scientific community over how the process of domestication works. Some researchers give credit to natural selection, wherein mutations outside of human control make some members of a species more compatible to human cultivation or companionship. Others have shown that carefully controlled selective breeding is responsible for many of the collective changes associated with domestication. These categories are not mutually exclusive and it is likely that natural selection and selective breeding have both played some role in the processes of domestication throughout history.
The domestication of wheat provides an example of how natural selection and mutation can play a key role in the process. Wild wheat falls to the ground to reseed itself when it is ripe, but domesticated wheat stays on the stem when it is ripe. 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 the only wheat harvested and became the seed for the next crop. This wheat was much more useful to farmers and became the basis for the various strains of domesticated wheat that have since been developed.
The example of wheat has led some to speculate that mutations may have been the basis for other early instances of domestication. It is speculated that a mutation made some wolves less wary of humans. This allowed these wolves to start following humans to scavenge for food in their garbage dumps. Presumably something like a symbiotic relationship developed between humans and this population of wolves. The wolves benefited from human food scraps, and humans may have found that the wolves could warn them of approaching enemies, help with hunting, carry loads, provide warmth, or supplement their food supply. As this relationship evolved, humans eventually began to raise the wolves and breed the types of dogs that we have today.
Nonetheless, some researchers maintain that selective breeding rather than mutation or natural selection best explains how the process of domestication typically worked. Some of the most well-known evidence in support of selective breeding comes from an experiment by Russian scientist, Dmitri 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 fox 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. More importantly, these foxes had floppy ears, smaller skulls, rolled tails and other traits commonly found in dogs.
Despite the success of this experiment, some scientists believe that selective breeding cannot always achieve domestication. They point out that known attempts to domesticate several kinds of wild animals in this way have failed repeatedly. The zebra is one example. It is possible that the historical process of domestication cannot be fully explained by any one principle acting alone. Some combination of natural selection and selective breeding may have played a role in the domestication of the various species that humans have come into close contact with throughout history.
Domestication of animals
- 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) are less expensive to keep in captivity. Most carnivores can only be fed meat, which requires the expenditure of many herbivores.
- 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 and cheetah are difficult to breed 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. Although similar to domesticated pigs in many ways, American peccaries and Africa's warthogs and bushpigs are also dangerous in captivity.
- Temperament which makes it unlikely to panic — A creature with a nervous disposition is difficult to keep in captivity as they will attempt to flee whenever they are startled. The gazelle is very flighty and it has a powerful leap that allows it to escape an enclosed pen.
- Modifiable social hierarchy — Social creatures that recognize a hierarchy of dominance can be raised to recognize a human as its pack leader. Bighorn sheep cannot be herded because they lack a dominance hierarchy, whilst antelopes and giant forest hogs are territorial when breeding and cannot be maintained in crowded enclosures in captivity.
A herding instinct arguably aids in domesticating animals: tame one and others will follow, regardless of chiefdom.
Domestication of plants
Given agriculture's importance to humans, the domestication of plants is even more important than the domestication of animals. The earliest human attempts at plant domestication occurred in Asia by 10,000 BC and involved the bottle gourd (Lagenaria siceraria) plant, used as a pre-ceramic technology container. The domesticated bottle gourd had reached the Americas from Asia by 8000 BC, probably with peoples migrating into the continent from Asia. 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.
Domestication was gradual, a process of trial and error that occurred slowly. 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 different parts of the world very different species were domesticated. In the Americas squash, maize, and beans formed the core of the diet. In East Asia rice, and soy were the most important crops. Some areas of the world such as Southern Africa, Australia and California and southern South America never saw local species domesticated.
Over the millennia many domesticated species have become utterly unlike their natural ancestors. Corn cobs are now dozens of times the size of their wild ancestors. A similar change occurred between wild strawberries and domesticated strawberries.
See also: Cultigen
Degrees of domestication
The boundaries between surviving wild populations and domestic clades of elephants, for example, can become vague. This is due to their slow growth. Similar problems of definition arise when, for example, domesticated cats go feral. A classification system that can help solve this confusion might be set up on a spectrum of increasing domestication:
- Wild: These species experience their full life cycles without deliberate human intervention.
- Raised at zoos or botanical gardens: These species are nurtured and sometimes bred under human control, but remain as a group essentially indistinguishable in appearance or behavior from their wild counterparts. (It should be noted that zoos and botanical gardens sometimes exhibit domesticated or feral animals and plants such as camels, dingos, mustangs, and some orchids.)
- Raised commercially: These species are ranched or farmed in large numbers for food, commodities, or the pet trade, but as a group they are not substantially altered in appearance or behavior. Examples include the honeybee, elephant, ostrich, deer, alligator, cricket, pearl oyster, and ball python. (These species are sometimes referred to as partially domesticated.)
- Domesticated: These species or varieties are bred and raised under human control for many generations and are substantially altered as a group in appearance or behavior. Examples include the Canary, Pigeons, the Budgerigar, the peach-faced Lovebird, dogs, cats, sheep, cattle, chickens, llamas, guinea pigs and laboratory mice.
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 and probably the Australian dingo. 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. One dividing line is whether a specimen born to wild parents would differ in 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.
Limits of domestication
Despite long enthusiasm about revolutionary progress in farming, few crops and probably even fewer animals ever became domesticated. While the process continues with plants (berryfruits, for example), it appears to have ceased with animals.
Domesticated species, when bred for tractability, companionship or ornamentation rather than for survival, can often fall prey to disease: several sub-species of apples or cattle, for example, face extinction; and many dogs with very respectable pedigrees appear prone to genetic problems.
One side-effect of domestication has been disease. For example, cattle have given humanity various viral poxes, measles, and tuberculosis; pigs gave influenza; and horses the rhinoviruses. Humans share over sixty diseases with dogs. Many parasites also have their origins in domestic animals.