Domestication refers to a population of animals (although it can also be used to refer to plants) or even a species as a whole. 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, transportation and to enjoy as pets or ornamental plants. Plants domesticated primarily for aesthetic enjoyment in and around the home are usualy 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.
Process of domestication
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.
Plant Domestication Usually Involves the Following Changes
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)
