Domestication

Domestication (from Latin domesticus) or taming is the process whereby a population of animals or plants, through a process of selection, becomes accustomed to human provision and control. A defining characteristic of domestication is artificial selection by humans. Some species such as the Asian Elephant, numerous members of which have for many centuries been used as working animals, are not domesticated ^[1] because they have not normally been bred under human control, even though they have been commonly tamed. 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 for scientific research, such as finding cures for certain diseases 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). Likewise, animals domesticated for home companionship are usually called pets while those domesticated for food or work are called livestock or farm animals.

Contents 1 Background 1.1 Animals 1.2 Plants 2 Degrees 3 Limits 4 Dates and places 4.1 Approximate dates and locations of original domestication 4.2 Modern instances 4.3 Former instances 4.4 Hybrid domestic animals 5 Genetic pollution 6 See also 7 References 8 External links

Background

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.^[2] Either way, a process of selection is involved. The domestication of wheat is an example of this. 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.^[3]

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.

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 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. 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. Despite the fact that four species of zebra are interbreedable with and part of the same genus as the horse and the donkey, attempts at domestication have failed.^[4] The factors which influence 'domesticatability' of large animals (see below) are discussed in some detail in ^[5]. Surprisingly only 14 species of large animal seem to be capable of domestication. In approximate order of their earliest domestication these are: dog, sheep, goat, pig, cow, horse, donkey, water buffalo, llama/alpaca, bactrian camel, and Arabian camel.

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), particularly food that is not utilized by humans (such as grass 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.
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, antelope and giant forest hog are territorial when breeding and cannot be maintained in crowded enclosures 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; 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 bushpig 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 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 the 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 the pack leader.

Plants

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 (circa 11,050 BP) contexts at Abu Hureyra in Syria^[6], 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^[7].

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 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:^[8]

• Higher germination rates
• More predictable & synchronous germination
• Increased size of reproductive organs
• A tendency for ripe seeds to stay on the plant, rather than breaking off and falling to the ground
• Reduced physical and chemical defences
• Change in biomass allocation (more in fruits, roots, or stems, depending on human)

Degrees

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:

• 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, 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.

Limits

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^[9].

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.

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". 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.^[10]

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.^[11][12] 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 9500 BC.^[13][14][15]

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

Species	Date	Location
Dog (Canis lupus familiaris)	15000 BCE [16]	East Asia and Africa
Sheep (Ovis orientalis aries)	between 9-11000 BCE[17][18]	Southwest Asia
Pig (Sus scrofa domestica)	9000 BCE[19]	Near East, China
Goat (Capra aegagrus hircus)	8000 BCE [20]	Iran
Cow (Bos primigenius taurus)	8000 BCE[21][22]	India, Middle East, and Sub-Saharan Africa
Cat (Felis catus)	7500 BCE [13][14][15][23]	Cyprus and Near East
Chicken (Gallus gallus domesticus)	6000 BCE[24]	India and Southeast Asia
Guinea pig (Cavia porcellus)	5000 BCE[25]	Peru
Donkey (Equus africanus asinus)	5000 BCE[26][27]	Egypt
Domesticated duck (Anas platyrhynchos domesticus)	4000 BCE	China
Water buffalo (Bubalus bubalis)	4000 BCE	India, China
Horse (Equus ferus caballus)	4000 BCE[28]	Eurasian Steppes
Dromedary (Camelus dromedarius)	4000 BCE	Arabia
Llama (Lama glama)	3500 BCE	Peru
Silkworm (Bombyx mori)	3000 BCE	China
Reindeer (Rangifer tarandus)	3000 BCE[29]	Russia
Rock pigeon (Columba livia)	3000 BCE	Mediterranean Basin
Goose (Anser anser domesticus)	3000 BCE[30]	Egypt
Bactrian camel (Camelus bactrianus)	2500 BCE	Central Asia
Yak (Bos grunniens)	2500 BCE	Tibet
Banteng (Bos javanicus)	Unknown	Southeast Asia, Java Island
Gayal (Bos gaurus frontalis)	Unknown	Southeast Asia
Alpaca (Vicugna pacos)	1500 BCE	Peru
Ferret (Mustela putorius furo)	1500 BCE-	Europe
Muscovy Duck (Cairina momelanotus)	Unknown	South America
Guineafowl	Unknown	Africa
Common carp	Unknown	East Asia
Domesticated turkey	500 BCE	Mexico
Goldfish	Unknown	China
European Rabbit	1600 BCE	Europe

Second circle

Species	Date	Location
Zebu (Bos primigenius indicus)	8000 BCE	India
Honey bee	4000 BCE	Multiple places
Asian Elephant	2000 BCE	Indus Valley civilization
Fallow Deer	1000 BCE	Mediterranean Basin
Indian Peafowl	500 BCE	India
Barbary Dove	500 BCE	North Africa
Japanese Quail (see Quail)	1100–1900	Japan
Canary	1600	Canary Islands, Europe
Mandarin Duck	Unknown	China
Mute Swan	1000–1500	Europe

Modern instances

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.^[31]

Former instances

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^[32], the Kakapo, the Ring-tailed Cat, Cheetah, Caracal and Bos aegyptiacus.

Hybrid domestic animals

• Alpaca: DNA evidence shows that alpacas are a llama/vicuña hybrid
• Beefalo
• Bengal cat
• Cama (animal)
• Chausie
• Cheetoh
• Coydog
• Dzo
• Sheep-goat hybrid
• Hinny
• Huarizo
• Iron Age Pig
• Mule
• Savannah (cat)
• Tiglon
• Wolfdog
• Wolphin
• Yakalo
• Zeedonk
• Zetland
• Zorse
• Zony
• Zubron

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, 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.

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
  • Experimental evolution
  • Feral
  • Gene pool
  • Genetic erosion
  • Genetic pollution
  • Genetic engineering
  • Horticulture
  • Hybrid
  • Lion taming
  • Marker assisted selection
  • Military animals
  • Selective breeding
  • Self-domestication
  • Wildness
  • Wildlife
• Related
  • Domestication theory describes the process of the 'taming' or appropriation of technology by its users.

References

External links

• Discussion of animal domestication
• Guns, Germs and Steel by Jared Diamond (ISBN 0-393-03891-2)
• News story about an early domesticated cat find
• Belyaev experiment with the domestic fox
• Use of Domestic Animals in Zoo Education
• The Initial Domestication of Cucurbita pepo in the Americas 10,000 Years Ago
• Cattle domestication diagram
• Major topic "domestication": free full-text articles (more than 100 plus reviews) in National Library of Medicine
• Why don't we ride zebras? an online children's film about animal domestication