Domestication

Domestication refers to the process whereby a population of animals or plants becomes accustomed to human provision and control. Humans have brought these populations under their 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 or protection), for protection of themselves and livestock, 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 or work are called livestock or farm animals.

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Process

There is debate within the scientific community over how the process of domestication works. Some researchers give credit to natural selection, where 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-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. 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.

Animals

According to evolutionary biologist Jared Diamond, animal species must meet six criteria in order to be considered for domestication:

1. 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.
2. 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.
3. 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.
4. 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.
5. 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. Some animals, such as Domestic sheep, still have a strong tendency to panic when their flight zone is crossed. 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.
6. Modifiable social hierarchy — Social creatures that recognize a hierarchy of dominance can be raised to recognize a human as its pack leader. Antelope and giant forest hogs are territorial when breeding and cannot be maintained in crowded enclosures in captivity.

Plants

See also: Agriculture and Agronomy

The earliest human attempts at plant domestication occurred in 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 (ca. 11,000 BC) 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 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, probably with peoples migrating into the continent from Asia.^[1]

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, beans, and perhaps manioc (also known as cassava) formed the core of the diet. In East Asia millets, 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

The results/effects of plant domestication include:^{[citation needed]}

• Higher germination rates
• Greater germination predictability
• More uniform timing of germination
• Increased size of reproductive organs
• Reduced complexity of reproductive organs
• Reduction of toxicity (humans select against self defense mechanisms)
• Change in biomass allocation (more in fruits, roots, or stems, depending on human preference)
• Change in life cycle (normally from perennial to annual for seed crops, and from annual to biennial for vegetable crops)

Degrees

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 populations experience their full life cycles without deliberate human intervention.
• Raised in captivity (in zoos or botanical gardens): These populations are nurtured and sometimes bred under human control, but remain as a group essentially indistinguishable in appearance or behaviour from their wild counterparts. (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, but as a group they are not substantially altered in appearance or behavior. Examples include the elephant, ostrich, 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 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. 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

Despite long enthusiasm about revolutionary progress in farming, few crops and probably even fewer animals ever became domesticated.

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.

Dates and places

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". 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 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. 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 which characterizes 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 7500 BC.

The earliest secure evidence of horse domestication, bit wear on horse molars at Dereivka in Ukraine, dates to around 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 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.

Approximate dates and locations of original domestication

Second circle

Modern instances

A project is underway to that is attempting to find the genetic basis for taming. Researchers at the Max Planck institute have reared two sets of rats. One set has been selected for aggressive traits and another for more tame traits. The researcher hope to mimic the process by which neolithic farmers first domesticated animals.^[16]

Former instances

Some species are said to have been domesticated, but are not any more, either because they have totally disappeared, or since only their domestic form no longer exists. An example would be the African and Asian elephants (See War elephant) and Bos aegyptiacus.

Hybrid domestic animals

• Beefalo
• Bengal cat
• Cama (animal)
• Chausie
• Cheetoh
• Coydog
• Dzo
• Sheep-goat hybrid
• Hinny
• Huarizo
• Iron Age Pig
• Mule
• Savannah (cat)
• Tigron
• Wolfdog
• Wolphin
• Yakalo
• Zeedonk
• Zobo (animal)
• Zorse
• Zony
• Zubron

Genetic pollution

Main article: Genetic pollution

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 a times threatening rare species with extinction. Cases include the mallard duck, wild boar, the rock dove or pigeon, the Red Junglefowl (Gallus gallus) (ancestor of all chickens), carp, and more recently salmon^{[citation needed]}. 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 rabbit. 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.^{[citation needed]}

See also

• Lists and timelines
  • List of domesticated animals
  • List of domesticated plants
  • List of domesticated fungi and microorganisms
  • Timeline of agriculture and food technology
• Articles
  • Animal husbandry
  • Columbian Exchange
  • Domestication of the horse
  • Feral
  • Gene pool
  • Genetic erosion
  • Genetic pollution
  • Genetic engineering
  • Horticulture
  • Hybrid
  • Lion taming
  • Military animals
  • Pedomorphosis
  • Selective breeding
  • Turkey (domesticated)
  • Wildness
  • Wildlife
• Related
  • Domestication theory describes the process of the 'taming' or appropriation of technology by its users.

References