托福阅读练习材料--DNA Wrath of Khan

　　历史上的许多著名统治者都热衷于政府他国，这样做的原因居然也可以用基因科学来解释。下面的新托福考试阅读练习资料中我们就来讨论一下有关基因的话题。

　　Today, Afghanistan is a war-torn region, battled over by military forces and world-spanning empires. Eight hundred years ago things were much the same. Only then, there was only one ruler: Genghis Khan.

　　Khan is one of the greatest conquerors who ever lived. Before he was finished, he had created an empire that ran all the way from the Caspian Sea to the Sea of Japan.

　　That’s the history portion of our show. Now, on to the science. What is it that powerful males of the human species are after when they overrun other males? From an evolutionary point of view, the major objective is to spread their genes more effectively. And surprising, new data suggest Khan may have done that more successfully than anyone imagined.

　　Researcher Tatiana Zerjal, from the University of Oxford in England, and a team of geneticists took genetic samples of over twenty-one thousand men from all over Asia. They were looking for variations in certain genetic “markers,” or sequences of genes that tell you something about where people came from. To their astonishment, they found that one out of every twelve Asian men in regions once part of the Mongol empire carry a form of the Y chromosome that can be traced to Mongolia a thousand years ago. How did this genetic tag become so widespread?

　　Khan, they suggest. There is reason to believe that Khan himself, and thus his long-ruling descendants, had this particular form of Y chromosome. And though his power is long faded, the genetic empire of the conqueror is going strong–in roughly one out of every two hundred men alive today.