Dogs and sheep were among the first animals to be domesticated.
US livestock inventory figures for 2004
|Animal ||Number |
|Pigs ||58,901,000 |
|Cows kept for beef ||42,947,000 |
|Total cows ||52,099,000 |
|Total cattle ||95,233,000 |
|Edit this table here (http://en.wikipedia.org/w/wiki.phtml?title=Template:US_Livestock_2004&action=edit) |
Domesticated animals, plants, and other organisms are those whose collective behavior, life cycle, or physiology has been altered as a result of their breeding and living conditions being under human control for multiple generations. Humans have brought these populations under their care for a wide range of reasons: for help with various types of work, to produce food or valuable commodities (such as wool, cotton, or silk), and to enjoy as pets or ornamental plants.
Domestication of technology is also a theory of how new technologies are 'tamed' or appropriated by society.
Process of domestication
There is debate within the scientific community over the how the process of domestication works. Some researchers give credit to mutations outside of human control for making 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. Theorists also note that natural selection probably played a role in the domestication of some species. These categories are not mutually exclusive and it is likely that mutations, selective breeding, and natural selection have all played some role in the process of domestication throughout history.
The domestication of wheat provides an example of how 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 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 lead 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. Other theorists have pointed out that natural selection rather than a random mutation could also be used to explain this process. Wolves that were more comfortable eating food scraps near human settlements would have had an advantage over other wolves. They would have been more likely to survive and pass on their tolerance of humans to the next generation. Thus the process of domestication would have started naturally before any human intervention or selective breeding was involved.
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, Dmitry Belyaev, in the 1950s. His team spent many years breeding the silver fox (Vulpes vulpes) and selecting only those individuals that showed the least fear of humans. Eventually, Belyaev's team selected only those that showed the most positive response to humans. He ended up with a population of grey fox whose behavior and appearance was significantly changed. These foxes no longer showed any fear of humans and often wagged their tails and lick their human caretakers to show affection.
Despite the success of this experiment, it is clear that selective breeding cannot always achieve domestication. Attempts to domesticate several kinds of wild animals in this way have failed repeatedly. The zebra is one example. The historical process of domestication cannot be fully explained by any one principle acting alone. Some combination of mutation, natural selection, or selective breeding has played a role in the domestication of the various species that humans have come into close contact with throughout history.
Domestication of animals
According to physiologist Jared Diamond, animal species must meet six criteria in order to be considered for domestication:
- 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 are less expensive to keep in captivity. Most carnivores can only be fed meat, which requires the expenditure of many herbivores.
- Reasonably fast growth rate — Fast maturity rate compared to the human life span allows breeding intervention and make 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 breed in captivity — Creatures that are reluctant to breed when kept in captivity do not produce useful offspring, and instead are limited to capture in their wild state. Creatures such as the panda and cheetah are difficult to breed in captivity.
- Pleasant disposition — Large creatures that are aggressive toward humans are dangerous to keep in captivity. The African buffalo has an unpredictable nature and is highly dangerous to humans.
- Temperament which makes it unlikely to panic — A creature with a nervous disposition is difficult to keep in captivity as they will attempt to flee whenever they are startled. The gazelle is very flighty and it has a powerful leap that allows it to escape an enclosed pen.
- Modifiable social hierarchy — Social creatures that recognize a hierarchy of dominance can be raised to recognize a human as its pack leader.
A herding instinct arguably aids in domesticating animals: tame one and others will follow, regardless of chiefdom.
Domestication of plants
Given agriculture's importance to humans, the domestication of plants is even more important than the domestication of animals. Plants were first domesticated around 9000 BCE in the Fertile Crescent in the Middle East. The first plants domesticated were generally annuals with large seeds or fruits. These included certain pulses such as peas and grains such as wheat.
The Middle East was especially suited to these species; the dry climate was conducive to large seeds, and the variety of elevations lead to a great variety of species. As it took place humans began to move from a nomadic hunter-gatherer society to a settled agricultural society. This change eventually lead, some 4000 to 5000 years later, to the first city states and eventually the rise of civilization itself.
Domestication was gradual, a process of trial and error that occurred slowly. Over time perennials and small trees began to be domesticated including apples and olives. Some plants were not domesticated until recently such as the macadamia nut and the pecan.
In different parts of the world very different species were domesticated. In the Americas squash, maize, and beans formed the core of the diet. In East Asia rice, and soy were the most important crops. Some areas of the world such as Australia 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 and domesticated strawberries.
Degrees of domestication
The boundaries between surviving wild populations and domestic clades of elephants, for example, can become vague. This is due to their slow growth. Similar problems of definition arise when, for example, domesticated cats go feral. A classification system that can help solve this confusion might be set up on a spectrum of increasing domestication:
- Wild: These species experience their full life cycles without deliberate human intervention.
- Raised at zoos or botanical gardens: These species are nurtured and sometimes bred under human control, but remain as a group essentially indistinguishable in appearance or behavior from their wild counterparts. (It should be noted that zoos and botanical gardens sometimes exhibit domesticated or feral animals and plants such as camels, dingoes, mustangs, and some orchids.)
- Raised commercially: These species are ranched or farmed in large numbers for food, commodities, or the pet trade, but as a group they are not substantially altered in appearance or behavior. Examples include the ostrich, deer, alligator, cricket, pearl oyster, and ball python. (These species are sometimes referred to as partially domesticated.)
- Domesticated: These species or varieties are bred and raised under human control for many generations and are substantially altered as a group in appearance or behavior. Examples include the dog, sheep, cattle, chicken, guinea pig and laboratory mice.
This classification system does not account for several complicating factors: genetically modified organism, feral populations, and hybridization. Many species that are farmed or ranched are now being genetically modified. This creates a unique category because it alters the organisms as a group but in ways unlike traditional domestication. Feral organisms are members of a population that was once raised under human control, but is now living and multiplying outside of human control. Examples include mustangs and probably the Australian dingo. Hybrids can be wild, domesticated, or both: a liger is a hybrid of two wild animals, a mule is a hybrid of two domesticated animals, and a beefalo is a cross between a wild and a domestic animal.
A great difference exists between a tame animal and a domesticated animal. The term "domesticated" refers to an entire species or variety while the term "tame" can refer to just one individual within a species or variety. Humans have tamed many thousands of animals that have never been truly domesticated. These include the elephant, giraffes, and bears. There is debate over whether some species have been domesticated or just tamed. Some state that the elephant has been domesticated, while others argue the cat has never been. One dividing line is whether a specimen born to wild parents would differ in behavior from one born to domesticated parents. For instance a dog is certainly domesticated because even a wolf (genetically the origin of all dogs) raised from a pup would be very different from a dog.
History of domestication
The first domestic animal was probably the dog, possibly as early as 10000 BCE in the Natufian culture of the Levant, though there is evidence of and association between humans and wolves going back 150000 years. The next three - the goat, sheep and pig - were domesticated around 8000 BCE, all in western Asia. However, there is recent archaeological evidence from Cyprus of domestication of a type of cat by perhaps 7500 BCE: this might make the cat second. The cow followed around 6000 BCE. The horse was first domesticated (probably in northern Russia) around 4000 BCE. Local equivalents and smaller species were domesticated from the 2500s BCE.
The processes of domestication and the distribution of domesticated species were both radically affected by the establishment of regular contact between the Eastern and Western Hemispheres following the voyages of Christopher Columbus. This sudden increase in the transmission of organisms between the Eastern and Western Hemispheres is referred to as the Columbian Exchange.
Limits of domestication
Despite long enthusiasm about revolutionary progress in farming, few crops and probably even fewer animals ever became domesticated. While the process continues with plants (berryfruits, for example), it appears to have ceased with animals.
Domesticated species, when bred for tractability, companionship or ornamentation rather than for survival, can often fall prey to disease: several sub-species of apples or cattle, for example, face extinction; and many dogs with very respectable pedigrees appear prone to genetic problems.
One side-effect of domestication has been disease. For example, cattle have given humanity various viral poxes, measles, and tuberculosis; pigs gave influenza; and horses the rhinoviruses. Humans share over sixty diseases with dogs. Many parasites also have their origins in domestic animals.