人类正在加速进化

　　如今世界很多地方的人们都有充足的食物，生存繁殖比以往任何时候都更为容易，所以很容易以为人类已经停止了进化。但是一项颇具争议的新研究结果却不这么认为。据其分析，人类的进化速度非但不曾放缓，相反，在过去4万年里加快了速度，过去5000年更是加快了100倍。这意味着尽管有些人游走异乡，与异族人通婚，但各大洲大多数人正在变得越来越不同，他们的基因并没有越来越同质化。

　　1800个人类基因已加快了进化，占人类基因组的7%。大多数基因突变都因人口猛增而产生。人口增长时，基因突变也会增加，这就提升了产生有益的基因变体的机会，这种有益的基因变体将提升人类的生存能力，并在整个人群中传播(这和大群昆虫制造抗杀虫剂的基因的速度比小群快是同样道理)。

　　研究人员没有破译大部分进化的基因，但他们说其中很多似乎都是应对人类饮食变化，和人类农垦初期曾肆虐过的中毒疾病卷土重来的结果。有些基因突变使成人能够消化淀粉、脂肪酸和牛奶中的乳糖。还有些增强了人类抵御疟疾、爱滋病和黄热病等疾病的能力。

　　答案

　　Human Evolution Is Speeding Up

　　Plentiful food has made it easier than ever before to survive and reproduce in many parts of the world, so it's tempting to think that our species has stopped evolving. But a controversial new study says that isn't so .Far from slowing down, human evolution has sped up in the past 40,000 years and has become 100 times faster in the past 5,000 years alone, according to the analysis. This means that even though some people have been globe-trotters who interbreed, most humans on different continents are becoming more different, rather than blending together into one genetically homogenous race.

　　Evolution has accelerated in 1800 human genes, which encompass about 70/o of the human genome. Most of the mutations resulted from dramatic population booms. As populations expand, the number of mutations increases, boosting the chances for a beneficial genetic variant that can improve survival and sweep through a population (in the same way that a large population of insects develops a gene for resistance to a pesticide faster than a small population).

　　Although the researchers don't know the identity of most of the genes, they say quite a few appear to be responses to changes in diet and a new wave of virulent diseases that swept through human populations as they began farming. Some mutations allow adults to digest starch, fatty acids, and lactose in milk. Others improve the resistance to diseases, such as malaria, AIDS, and yellow fever.

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