Tameness is a fundamental precondition for domestication. Among the mammals exceptions are only found in some recent domesticates, like minks or other species bred for their pelts. In such cases, the necessary control over the animal is achieved by caging. Taming on the other hand provides mental control over the animal, which nevertheless must usually be supported by fencing or other suppressive means of physical control. However, many animal species can be tamed, but only a few of them became domesticates.
Domesticates are different from their wild relatives. A tamed wolf is not a dog. This indicates that taming is only a first step in the direction of domestication. For its completion it is necessary that tame individuals start to reproduce and that their offspring remain and breed under human control over several generations. During this time, both the circumstances of living together with humans and the direct results of human control will more or less consciously influence reproductive success of particular individuals. Thus, a selection of special biological traits will soon become manifest in an animal population, which is breeding under human control. As soon as clear differences can be observed, the respective population can be recognized as domesticated.
The domestication process thus requires the following steps:
1. gaining complete control over individual animals, preferably by taming;
2. assembling tamed (or otherwise controlled) groups of animals containing both sexes and keeping them together over periods long enough to start intra-group breeding; and
3. continued intragroup breeding of the tame (or otherwise controlled) stock and avoiding large-scale cross-breeding with the wild population.
The easiest way to achieve step 1 is the nursing of very young individuals taken from the wild population. The second step is the most difficult one, because it requires keeping the raised animals till sexual maturity and beyond. In addition these animals must be kept in a way, which allows for their repertoire of reproductive behavior to be performed successfully. Once these difficulties are overcome, the third step will become easier and easier with each successful breeding cycle, because there will be a very efficient natural selection for animals that are capable to survive and reproduce under these particular circumstances. In addition, human selection will favor particular external features, which help to distinguish domestic and wild stock - like aberrant colorations, hanging ears or twisted horns, etc. Early breeders will soon have realized that cross-breeding with wild animals is not desirable, because such crosses will have hampered the accumulation of those inherited behavioral features which are favorable for a close coexistence with humans.
A widespread hypothesis of how step 1 might have been achieved during the domestication of meat-producing animals is based on the assumption of some kind of management of wild animal populations through human hunters. This has remained a theoretical concept, though, lacking reflections on the practicability of such management. Actually, specialized hunters must have had some sort of control over their favorite prey animals. This control, however, is achieved by monitoring, not restricting, the movements of a wild animal population. Selective pressures exerted by specialized hunters will have favored better avoidance on the animal side, not a mutual approach. Real physical control of hunters over a mature wild population is absolutely illusive in the case of wild sheep or goats in their natural mountainous habitats, because their ability to move in such terrain is by far superior to that of humans. Other animals, like wild cattle, are simply too strong as adults to be physically controlled. Only in theory, fencing would have been a way to obtain control over a mature population of wild herbivores, because a fenced area would either have been too small to provide fodder for a long enough period, or too large to sufficiently restrict the movements of the animals. In conclusion, it remains difficult to imagine realistic scenarios for a domestication process starting from a mature wild animal population within its natural habitat.
World History
