Herding instinct

 作者:俞狂裔     |      日期:2019-03-07 06:07:03
By Emma Young, San Francisco From the annual meeting of the American Association for the Advancement of Science in San Francisco Genetic analysis of livestock suggests our ancient ancestors in Asia and in Europe achieved simultaneous farming feats – the domestication of pigs, sheep, water buffalo and cattle. In 1994, Daniel Bradley at Trinity College Dublin studied the mitochondrial DNA of modern cattle, and concluded that their ancestors were domesticated twice, at two sites separated by thousands of miles. Now his analysis of DNA data from modern pigs, sheep and water buffalo has thrown up the same “striking” differences in the genetic profiles of animals in different parts of the modern world. “We found that in cattle, there are two separate foci of genetic diversity in the mitochondrial DNA, and it seemed likely we were looking at two separate captures from the wild. Now we have found that this duality runs right through sheep, pigs and water buffalo. There is the same theme of east and west,” Bradley says. The DNA data suggests that cattle were domesticated between 8,000 and 10,000 years ago in the Fertile Crescent of the Levant (which stretches through Turkey, Jordan and Iraq) and in the Indus valley. Sheep were also first herded by people in the same areas. Pigs were domesticated in the Fertile Crescent, and probably in China, while the water buffalo was first domesticated in southern China and at another as yet unidentified location further west. Bradley’s team looked at mitochondrial DNA, Y chromosomes and DNA markers called microsatellites. All three sets of data threw up striking differences between groups of animals living in different parts of the world. Bradley concludes that the animals descended from two separate groups of common ancestors, domesticated at roughly the same time. However, the data do not prove that two entirely separate ‘captures’ of wild animals took place. Bradley admits it is possible that humans domesticated an animal, and moved with it. When they settled an area that was home to a distantly related species, interbreeding could have created the second distinct genetic profile. But other researchers support Bradley’s hypothesis. “With domestication, you’re selecting for behaviour,” says Melinda Zeder of the Smithsonian Institution in Washington. “Wherever there are wild animals with suitable characteristics and the right population densities and environmental conditions, this can trigger relationships with people. This can happen in many different areas of the world.” Previous research has shown that the goat was the first animal to be domesticated. This took place in the Fertile Crescent just under 10,