人類正在加速進(jìn)化

　　如今世界很多地方的人們都有充足的食物，生存繁殖比以往任何時(shí)候都更為容易，所以很容易以為人類已經(jīng)停止了進(jìn)化。但是一項(xiàng)頗具爭議的新研究結(jié)果卻不這么認(rèn)為。據(jù)其分析，人類的進(jìn)化速度非但不曾放緩，相反，在過去4萬年里加快了速度，過去5000年更是加快了100倍。這意味著盡管有些人游走異鄉(xiāng)，與異族人通婚，但各大洲大多數(shù)人正在變得越來越不同，他們的基因并沒有越來越同質(zhì)化。

　　1800個(gè)人類基因已加快了進(jìn)化，占人類基因組的7%。大多數(shù)基因突變都因人口猛增而產(chǎn)生。人口增長時(shí)，基因突變也會(huì)增加，這就提升了產(chǎn)生有益的基因變體的機(jī)會(huì)，這種有益的基因變體將提升人類的生存能力，并在整個(gè)人群中傳播(這和大群昆蟲制造抗殺蟲劑的基因的速度比小群快是同樣道理)。

　　研究人員沒有破譯大部分進(jìn)化的基因，但他們說其中很多似乎都是應(yīng)對(duì)人類飲食變化，和人類農(nóng)墾初期曾肆虐過的中毒疾病卷土重來的結(jié)果。有些基因突變使成人能夠消化淀粉、脂肪酸和牛奶中的乳糖。還有些增強(qiáng)了人類抵御瘧疾、愛滋病和黃熱病等疾病的能力。

　　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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