Dogs and
sheep were among the first animals to be domesticated
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."[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 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. 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.[citation needed]
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 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.[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.[citation needed]
According to evolutionary biologist Jared Diamond, animal species must meet six criteria in order to be considered for domestication:[6]
Hereford cattle, domesticated for beef production.
- 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.
- 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 bushpig are 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 the domestic 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.
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.
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 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.[citation needed]
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.[citation needed]
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.[citation needed]
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.[citation needed]
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.[citation needed]
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.[citation needed]
Domesticated plant species often differ from their wild relatives in predictable ways. These differences are called the domestication syndrome, and include:[10]
- 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 needs).
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:[citation needed]
- Wild: These populations experience their full life cycles without deliberate human intervention.[citation needed]
- 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.)[citation needed]
- 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.)[citation needed]
- 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.[4]
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.[citation needed]
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] Similar problems of definition arise when domesticated cats go feral.
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[citation needed]. 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.[citation needed]
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.[citation needed]
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.[citation needed]
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.[citation needed]
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.[citation needed]
There is early evidence of beekeeping, in the form of rock paintings, dating to 13,000 BC.[citation needed]
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.[citation needed]
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.[citation needed]
Second circle
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.[citation needed]
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.[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 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.[citation needed]
- Lists and timelines
- Articles
- Related
- ^ See Article 2 (Use of Terms) of the Convention on Biological Diversity
- ^ a b c Diamond, Jared (1999). Guns, Germs, and Steel. New York: Norton Press. ISBN 0-393-31755-2.
- ^ Zohary, D. & Hopf, M. (2000). Domestication of Plants in the Old World Oxford: Oxford Univ. Press.[page needed]
- ^ a b Lyudmila N. Trut (1999). "Early Canid Domestication: The Farm-Fox Experiment" (PDF). American Scientist (Sigma Xi, The Scientific Research Society) 87 (March–April): 160–169. http://www.hum.utah.edu/~bbenham/2510%20Spring%2009/Behavior%20Genetics/Farm-Fox%20Experiment.pdf. Retrieved 2011-06-25.
- ^ Clutton-Brock, J. (1981) Domesticated Animals from Early Times. Austin: Univ. Texas Press.[page needed]
- ^ Diamond, Jared (1998). Guns, Germs, and Steel. Vintage. pp. 169–174. ISBN 978-0-09-930278-0.
- ^ http://www.messybeast.com/cathistory.htm
- ^ Hillman G, Hedges R, Moore A, Colledge S, Pettitt P (2001). "New evidence of Lateglacial cereal cultivation at Abu Hureyra on the Euphrates". Holocene 11 (4): 383–393. DOI:10.1191/095968301678302823. http://hol.sagepub.com/cgi/content/abstract/11/4/383.
- ^ Erickson DL, Smith BD, Clarke AC, Sandweiss DH, Tuross N (December 2005). "An Asian origin for a 10,000-year-old domesticated plant in the Americas". Proc. Natl. Acad. Sci. U.S.A. 102 (51): 18315–20. DOI:10.1073/pnas.0509279102. PMC 1311910. PMID 16352716. http://www.pnas.org/content/102/51/18315.full.
- ^ http://www.plantsciences.ucdavis.edu/gepts/pb143/lec08/pb143l08.htm
- ^ Virányi Z, Gácsi M, Kubinyi E, Topál J, Belényi B, Ujfalussy D, Miklósi Á (2008). "Comprehension of human pointing gestures in young human-reared wolves (Canis lupus) and dogs (Canis familiaris)". Animal Cognition 11 (3): 373–387. DOI:10.1007/s10071-007-0127-y.
- ^ Berry, R.J. (1969). "The Genetical Implications of Domestication in Animals". In Ucko, Peter J., Dimbleby, G.W.. The Domestication and Exploitation of Plants and Animals. Chicago: Aldine. pp. 207–217.
- ^ http://hcs.osu.edu/hcs/TMI/HCS210/HortOrigins/BrDomestic.html
- ^ Troy CS, MacHugh DE, Bailey JF, et al. (April 2001). "Genetic evidence for Near-Eastern origins of European cattle". Nature 410 (6832): 1088–91. DOI:10.1038/35074088. PMID 11323670.
- ^ Wendorf F., Schild R. (1998). "Nabta Playa and its role in ortheastern African prehistory". J. Anthropol. Archaeol 17 (2): 97–123. DOI:10.1006/jaar.1998.0319.
- ^ a b "Oldest Known Pet Cat? 9500-Year-Old Burial Found on Cyprus". National Geographic News. 2004-04-08. http://news.nationalgeographic.com/news/2004/04/0408_040408_oldestpetcat.html. Retrieved 2007-03-06.
- ^ a b Muir, Hazel (2004-04-08). "Ancient remains could be oldest pet cat". New Scientist. http://www.newscientist.com/article/dn4867.html. Retrieved 2007-11-23.
- ^ a b Walton, Marsha (April 9, 2004). "Ancient burial looks like human and pet cat". CNN. http://edition.cnn.com/2004/TECH/science/04/08/cats.cyprus/index.html. Retrieved 2007-11-23.
- ^ Dienekes' Anthropology Blog : Dog domestication in the Aurignacian (c. 32kyBP)
- ^ MSNBC : World's first dog lived 31,700 years ago, ate big
- ^ Scott & Fuller 1974, p. 54
- ^ Krebs, Robert E. & Carolyn A. (2003). Groundbreaking Scientific Experiments, Inventions & Discoveries of the Ancient World. Westport, CT: Greenwood Press. ISBN 0-313-31342-3.
- ^ Simmons, Paula; Carol Ekarius (2001). Storey's Guide to Raising Sheep. North Adams, MA: Storey Publishing LLC. ISBN 978-1-58017-262-2.
- ^ Giuffra E, Kijas JM, Amarger V, Carlborg O, Jeon JT, Andersson L (April 2000). "The origin of the domestic pig: independent domestication and subsequent introgression". Genetics 154 (4): 1785–91. PMC 1461048. PMID 10747069. http://www.genetics.org/cgi/pmidlookup?view=long&pmid=10747069.
- ^ G. Larson, K. Dobney, U. Albarella, M. Fang, E. Matisso-Smith, J. Robins, S. Lowden, H. Finlayson, T. Brand, E. Willerslev, P. Rowley-Conwy, L. Andersson, A. Cooper (March 2005). "Worldwide Phylogeography of Wild Boar Reveals Multiple Centers of Pig Domestication". Science 307 (5715): 1618. DOI:10.1126/science.1106927. PMID 15761152. http://www.sciencemag.org/content/307/5715/1618.full.pdf.
- ^ Melinda A. Zeder, Goat busters track domestication (Physiologic changes and evolution of goats into a domesticated animal), April 2000, (English) (summarizing research done in Ganj Dareh).
- ^ Late Neolithic megalithic structures at Nabta Playa (Sahara), southwestern Egypt.
- ^ Source : Laboratoire de Préhistoire et Protohistoire de l'Ouest de la France [1], (French).
- ^ [2], domestication of the cat on Cyprus, National Geographic.
- ^ West B., Zhou B-X. (1989). "Did chickens go north? New evidence for domestication" (PDF). World’s Poultry Science Journal 45 (3): 205–218. DOI:10.1079/WPS19890012. http://www.adelaide.edu.au/ANZCCART/publications/dom_chicken.pdf.
- ^ History of the Guinea Pig (Cavia porcellus) in South America, a summary of the current state of knowledge
- ^ Beja-Pereira A, England PR, Ferrand N, et al. (June 2004). "African origins of the domestic donkey". Science 304 (5678): 1781. DOI:10.1126/science.1096008. PMID 15205528. http://www.sciencemag.org/cgi/pmidlookup?view=long&pmid=15205528. [New Scientist Donkey domestication began in Africa Lay summary].
- ^ Roger Blench, The history and spread of donkeys in AfricaPDF (235 KiB) (English).
- ^ The Domestication of the Horse; see also Domestication of the horse
- ^ Domestication of Reindeer
- ^ Geese: the underestimated species
- ^ Nice Rats, Nasty Rats: Maybe It’s All in the Genes
- ^ .Sometimes it is because these animals don't breed well in captivity
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