What is domestication?
The domestication of animals, especially the hoofed mammals, has been practiced for centuries and has profoundly shaped the course of human history in the last 13,000 years. It contributed to the rise of civilization, single-handedly transformed global demography, and provides a sizable amount of our food and clothing today.
A prime example are horses, which were domesticated in southeast Europe 6,000 years ago. While their original purpose was riding, they also provided meat, milk, and long-distance transportation and warfare capabilities that led to the spread of Indo-European languages and culture and the transformation of ancient social orders.
In 1984, Price defined domestication as "that process by which a population of animals becomes adapted to man and to the captive environment by some combination of genetic changes occurring over generations and environmentally induced developmental events recurring over each generation." Price himself admits that this rather simplified definition of domestication does not allow for the possibility that genes and the environment may operate as independent factors that acted additively on each other. Lickliter and Ness in 1990 pointed out that the development of domestic physical characteristics can only be understood in terms of the complex interplay of organic and environmental factors during embryo development.
Both these definitions assume that the animals have been plucked from their ancestral wild environments and placed into a different, captive one. It also supposes that certain animal management and housing practices have been applied over time in rearing and maintaining each species in captivity.
How animals were selected for domestication
Both cultural and practical reasons have determined which animals were domesticated and where or when their domestication occurred. With the possible exception of the dog, domestication occurred when humans were faced a specific need and requirement that could only be fulfilled through corralling and breeding a certain animal population.
Although food supplies were available through hunting, fishing, and gathering in tropical regions, animals in those regions were domesticated as work animals or to provide fiber, as well as for food. The water buffalo (Bubalus bubalis), for example, was used primarily as a beast of burden and not for meat or milk.
Another issue that comes into play is whether the animal can be domesticated or not. Most wild animals avoid close human contact unless they have been habituated to the presence of people. The interaction of captive animals with humans thus plays a key factor in the domestication process. The degree of tameness in individual animals determines, to a large extent, the nature of that interaction.
Tameability, like tameness, is a desirable trait in animals undergoing domestication. We can surmise that some species, breeds, and individuals are more tameable than others, and that tameability is a heritable trait. The component of tameness, some argue, is not transmitted from mother to offspring.
In 1974, Blaxter determined that the offspring of handreared (very tame) ungulates, when exposed to people in the absence of members of their own species, exhibit similar flight distances from humans as the mother-reared (relatively untamed). Still, relatively untamed animals often show less fear of people in the presence of tame members of the same species. Lyons, Price, and Moberg reported that relatively untamed mother-reared dairy goats (Capra hircus) exhibited shorter flight distances from humans when exposed to people in the presence of tame herd-males.
The question of tameability may provide an answer to why, in a world that has provided 148 species weighing 99 lb (45 kg) or more, only 14 of those species have actually been domesticated. There are many cases in which only one out of a closely related group of species was successfully domesticated. Horses and donkeys, for example, were one of the first domesticates, but none of the four zebra species that are able to interbreed with them have been actually tamed. At the same time, while five of the most valuable domestic mammals—the goat, sheep, cow, pig, and horse—had all been domesticated repeatedly by 4,000 b.c., the sole addition within the last millennium has been the reindeer.
Ongoing efforts at domesticating other large wild mammals have often resulted in failure, as in the cases of the eland, elk, moose, musk ox, and zebra, or at best, have led to ranched
animals such as the deer and American bison that still cannot be herded and that have trivial economic value in comparison to the five most valuable domesticated mammals.
According to Diamond, the obstacle lies with the species itself, not with the local people. In the case of zebras, European horse breeders who settled in South Africa in the 1600s, like the African herders of previous millennia, gave up trying to domesticate zebras after several centuries. Zebras are exceptionally and incurably vicious, for one thing. Diamond recounts their nasty habit of biting a handler and not letting go until the handler is dead. They also have better peripheral vision than horses, which makes them impossible to lasso since they can see the rope coming and will flick away their head.
Other examples of species characteristics that stand in the way of domestication include: the tendency of gazelle and deer to grow territorial and violent against their keepers; the absence of follow-the-leader dominance hierarchies in antelope; and the fierce dispositions of rhinoceroses. Though elephants have been tamed and domesticated, their slow growth rate and long birth spacing provides an impediment to large-scale domestication.
Not all wild animals were recognized for their domestic value, however. The quagga (Equus quagga), a small, horselike animal from South Africa, was regarded as a pest and hunted to extinction despite its docile nature, potential ease of tameability, and resistance to diseases that plagued imported horses of European descent.
Domestication of the goat and sheep
Goats were first domesticated in the highlands of western Iran 10,000 years ago and were probably the first ruminants to be domesticated because of the presence of wild goats in regions where agriculture was developing. Archaeological evidence and carbon dating show a distinct shift toward the selective harvesting of young male goats. This probably marks initial human management and the transition from hunting to the herding of the species.
The ancestry of the domestic goat (Capra hircus) can be traced to wild goats (C. aegagrus) and the Nubian ibex (C. ibex) native to the canyon system. As it is difficult to distinguish between the bones of these two species, the exact percentages of each species in today's domestic goats are difficult to determine. According to Luckart and his co-workers, the earliest unambiguous fossil evidence of domestic goats was found in southwest Iran dating 9,000 years ago and in the Iranian plateau dating 10,000 years ago.
In the case of domestic sheep (Ovis aries), DNA sequencing and analyses carried out in 2002 provided strong evidence that they originated from two subspecies of the mouflon (O. musimon). The mouflon is a rare breed of primitive domestic sheep whose population is shrinking on the Mediterranean islands of Sardinia, Corsica, and Cyprus. However, it has been successfully introduced into central Europe, including Germany, Austria, Czech Republic, Slovak Republic, and Romania.
Many morphological, physiological, and behavioral traits characterize and distinguish domestic sheep and goats from their wild ancestors, such as diminished sexual dimorphism, decreased brain, body, and horn size, changes in horn shape, and even in the color of the coat. In 1998, Zohary and his colleagues proposed that these differences were shaped largely by unconscious selection. Once the founder herd had been assembled and controlled by humans, the transfer of these animals from their wild environments into the markedly different human-made husbandry system resulted in drastic changes in selection pressures. Several adaptations that were vital for survival in the wild then lost their fitness under the new conditions, subsequently breaking down through lack of use. New traits, which now characterize domestic sheep and
goats, were selected for instead. Protection from predators, culling of young males, protection from the elements, and changes in land use and in food and water supplies are considered the main ecological factors introduced by humans at the start of sheep and goat domestication.
Variation in the behavior patterns of different breeds of sheep, including level of tameness, has also been attributed to breeding under the control of humans as well as selection for productivity. Selection of rams for domestic behavior, for instance, often leads to hereditary changes of behavior diversity. When Lankin studied the domestic behavior of 11 breeds of sheep (O. aries) in 1997, he came to the conclusion that breeds subjected to intensive selection for commercial purposes tended to be tamer toward humans than "wilder" breeds. The East Fresian breed, which has been intensively selected for meat and milk production, for instance, is particularly tame toward humans. A few years later, Lankin found that "wild" ewes showed increased levels in the stress hormone corticosteriod when they were isolated, transported, or competing for feed. On the other hand, "domestic" ewes showed the greatest stress hormone response to being paired with another sheep in a cage.
Domestication of the cow
It is generally believed that cattle were first domesticated in southwest Asia, particularly Anatolia, or in southeast Europe, where their remains have been found in several sites dated between 9,000 and 8,000 years ago. Large bovid bones discovered at several small sites in the Western Desert of Egypt have been identified as belonging to domestic cattle. The bones were radiocarbon dated to between 9,500 and 8,000 years ago, raising the possibility that there was a separate, independent center for cattle domestication in northeast Africa. There remains, however, some contention about the identity and therefore, the validity of the bones.
A 2003 study suggests that Britons were harvesting milk as early as 6,000 years ago. Evershed and his University of Bristol colleagues examined over 950 broken pieces of crockery from 14 archaeological sites in Britain that date to the Neolithic, Bronze Age, and Iron Age. They found evidence of dairy consumption, although the ages of the milk-spotted pieces of pottery varied from site to site. The authors concluded that animals were already being exploited for milk at the time farming arrived in Britain in the late fifth millennium b.c.
Domestication of the pig
Domestication of the pig is likely to have occurred first in the Middle East about 9,000 years ago and may have occurred repeatedly from local populations of wild boars. The wild boar population, with at least 16 different subspecies proposed, is widespread in Eurasia and occurs in Northwest Africa. Historical
records indicate that Asian pigs were introduced into Europe during the eighteenth and early nineteenth centuries.
Modern domestic pigs show marked morphological differences when compared to their wild ancestors. However, it has not yet been established whether domestic pigs have a single or multiple origin.
In 1868, Darwin described two major forms of domestic pigs—a European and an Asian form. The former was assumed to originate from the European wild boar, while the wild ancestor of the latter was unknown. Darwin considered the two forms as distinct species on the basis of profound phenotypic differences. It is well documented that Asian pigs were used to improve European pig breeds during the eighteenth and early nineteenth centuries but to what extent Asian pigs have contributed genetically to different European pig breeds is unknown.
A 1998 study using microsatellite markers estimated the divergence between major European breeds and the Chinese Meishan breed at about 2,000 years. Some mitochondrial DNA studies during that time also indicated genetic differences between European and Asian pigs, but provide no estimate of the time the breeds diverged.
Finally, in 1999, an investigation aiming to provide a more comprehensive molecular analysis of the origin of domestic pigs evaluated wild and domestic pig populations from Asia and Europe. Giuffra and his fellow researchers came to the conclusion that the European and Asian subspecies of the wild boar were independently domesticated, and estimated the time since divergence of the ancestors for European and Chinese Meishan domestic pigs at 500,000 years ago. Their data showed that European domestic pigs and Chinese Meishan pigs are closely related to existing subspecies of the Eurasian wild boar (S. scrofa).
Domestication of the horse
The domestication of the horse facilitated the development of human civilization by providing the means of effective transport, agriculture, industry, and warfare.
Wild horses were widely distributed throughout the Eurasian steppe during the Upper Paleolithic around 35,000 to 10,000 years ago, but in many regions, they disappeared from the fossil record about 10,000 years ago. Today, only one supposed wild population, the Przewalski's horse (Equus caballus przewalskii), remains. Przewalski's horse is Extinct in the wild, but has lived in captivity and efforts are underway to reintroduce it into the wild.
Horse remains are common in archaeological sites of the Eurasian grassland steppe dating from about 6,000 years ago,
suggesting the time and place of their first domestication. Evidence from bit wear patterns on the teeth suggests that some horses could have been ridden.
There are two different hypotheses for the origin of the domestic horse (E. caballus) from wild populations. The "restricted origin" hypothesis suggests that the domestic horse was selectively and multigenerationally bred from a limited wild stock from a few domestication centers. The domestic horses were then distributed to other regions.
Another school of thought suggests that domestication involved a large number of founder animals recruited over an extended period of time throughout the extensive Eurasian range of the horse. In this "multiple origins" scenario, horses may have been captured from diverse wild populations and then increasingly bred in captivity as wild populations declined.
In 2001, an analysis of mitochondrial DNA from 191 domestic horses revealed a high diversity of matrilines, or lines of descent traced exclusively through female members from one founding female ancestor. This suggests that wild horses from a large number of populations were utilized as founders of the domestic horse. A single, geographically restricted population would have limited the founding lineages. The results also showed a bias toward females in ancient breeding and trade. This is consistent with modern breeding practices in which select studs are used for a much larger population of females.
Domestication of the camelids
Information on the presence and utility of camels in India from the proto-historic period to the present is supported by archaeological evidence, literature, and the arts. The camel in India has been an animal of utility from early Harappan level of civilization (c. 3000–1800 b.c.). One hypothesis suggests that the single-humped camel, or dromedary (Camelus dromedarius), was independently domesticated by the Indus people, while others are of the opinion that the domesticated double-humped camel was the species present in the Indus Valley during the third millennium b.c.
Because of the absence of detailed analysis of bones excavated from archaeological sites, scientists and archaeologists are hard-pressed to reach any conclusive identification regarding the species level of the ancient Indian camel. Today, the domestic bactrian camel (C. bactrianus) is on the verge of extinction in India, while the dromedary, boasting population
numbers of 1.1 million, is an important domesticate widely distributed throughout the northwestern parts of India.
Some debate rages over the origins of the guanaco (Lama guanicoe) and llama (L. glama) and if faunal remains from Andean archaeological sites can resolve this issue. Changes in incisor morphology during the domestication process suggest that the alpaca may be descended from the vicuña (Vicugna vicugna). A comparison of fiber production characteristics in preconquest and extant llama and alpaca breeds, however, indicates that extensive hybridization between the two species is likely to have occurred since European contact.
Consequences of domestication
The transition from the hunter-gatherer lifestyle to food production beginning around 8,500 b.c. enabled people to adopt a more sedentary lifestyle, rather than migrating to follow seasonal shifts in wild food supplies. (Some movement was still necessary with herds of domestic animals.) The production of food led to a human population explosion, since this lifestyle allowed shorter birth intervals.
Animal production did not come without a cost as it meant that humans had to share disease-causing microbes with the animals. Molecular studies of microbes have revealed the presence of their closest relatives in the domesticated animal species. The measles virus may have evolved from the rinderpest virus found in cattle. Smallpox virus may have evolved from cowpox virus. It has also been postulated that human influenza virus may have arisen from a mixture of influenza viruses in ducks and pigs.
The future of domestication?
In his 2002 paper on the past, present, and future of domestication, Diamond wondered aloud if the rise of molecular biology, genetics, and improved understanding of animal behavior might not allow the domestication of species that have proven undomesticable in the past. On the other hand, challenges exist with our existing varieties of domesticates, even as science and technology becomes increasingly sophisticated.
A study published online by the journal Nature Biotechnology provides a sneak peek into the possible future of dairy farming. Brophy and her coworkers at the Ruakura Research Center in New Zealand, took cells from female dairy cows and altered them to include additional copies of two genes that are instrumental in the production of the milk protein casein. The cells were then fused with donor eggs and implanted into surrogate mothers to bring to term. Out of the 11 cloned cows that managed to survive, only nine yielded milk with elevated levels of two casein molecules. Their milk had 8–20% more beta-casein and nearly twice as much kappa-casein as milk from regular dairy cows.
These enhanced properties of the milk should speed up the cheese manufacturing process and increase the cows' productivity. This was the first time that scientists have modified cow's milk solely to improve its quality instead of altering it to manufacturing proteins of pharmaceutical interest. The authors concluded that "the magnitude of the observed changes highlights the potential of transgenic technology to tailor milk composition in dairy cows."
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"Ungulate Domestication." Grzimek's Animal Life Encyclopedia. . Encyclopedia.com. (September 24, 2018). http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/ungulate-domestication
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