The history of domestic animals is an interesting question in its own right, and is intimately tied to the development of human civilization. In his book, Guns, Germs, and Steel, Prof. Jared Diamond cites the different availability of domesticable animal species in different parts of the world as one factor that significantly influenced the pace of human social development. His Table 9.2 illustrates the differences:
|Mammalian Species||Eurasia||Sub-Saharan Africa||Americas||Australia|
Diamond defines a candidate species as a herbivorous or omnivorous mammal species whose individuals, on average, weigh over 100 pounds (45 kg). His thesis is that a key reason that civilization (in the modern sense) developed first in Eurasia is that it had so many species available to be domesticated, and that so many were successfully domesticated.
One of the obstacles to domestication is the characteristic temperament of the animals in question. Although the zebra is in many respects very similar to the horse, it has an unfailingly nasty temper which tends to get worse as it gets older. According to Diamond, zebras injure more zoo keepers every year than do tigers. Similarly, although the African cape buffalo is a large animal that lives in herds, grows relatively quickly to a weight of about one ton, and is much better adapted to the local climatic conditions than ordinary cattle, it is widely regarded as one of the most dangerous animals in the world.
The process by which domestication took place historically has been something of a mystery. Charles Darwin thought that the process must have been very slow. But more recently, some alternative ideas have been advanced, and are outlined in an excellent survey article in the New Scientist. Briefly, the new conjecture, first advanced by a Russian geneticist, Dmitry Belyaev, of the Institute of Cytology and Genetics in Novosibirsk, is that humans initially selected the tamest animals for domestication; because Belyaev thought that tameness might be genetically linked, this would mean that domestication could occur more rapidly than had previously been believed.
The upshot is that the animals you end up taking home are the ones that are least perturbed by human company. If this behavioural trait has a genetic basis, you have already selected animals boasting genes for tameness. That, the bold Russian hypothesised, is a crucial step in domestication.
Belyaev started an experiment to test his idea. In 1959, he obtained a group of silver foxes from a nearby fur farm. These animals were already relatively tame, but he allowed only the tamest to breed. Within a handful of generations, some of the foxes had started to wag their tails and vocalize (bark) in the presence of humans. Before long, physical traits characteristic of domestic species, such as floppy ears and varied fur colors, began to appear. The tamer foxes also had higher average levels of the neuro-transmitter serotonin.
Belyaev also started an experiment with rats, in which he attempted to breed two strains: one tame, and one aggressive. This experiment also was successful. (The New Scientist article has a link to a short video demonstrating the behavior of the two groups.) Similar experiments were carried out with American minks and with river otters in Japan.
The results of these experiments suggest that Belyaev was right: far from the characteristic features of domesticated mammals requiring hundreds of generations of selective breeding, they start to appear in just a few. With all the animals, selecting for tameness brought with it new colour variants and altered reproduction, in fact pretty much all the features typical of a domesticated species.
The experimental program fell upon hard times after the collapse of the Soviet Union. However, a new program is now being carried out at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, under the direction of geneticist Svante Pääbo.
This is fascinating research, which could have a range of implications. Cape buffalo kill more people in Africa every year than lions, so finding a way to make them a little less cranky (Prozac?) could be a good thing. It might be a little over the top to want a pet zebra, but we might just gain some insights into human behavior and aggression, too.