万物简史 第595期:生命的物质(21)（在线收听）

By such means does Darwinian natural selection look after us. It also helps to explain why we are all so similar. Evolution simply won't let you become too different — not without becoming a new species anyway.

达尔文的自然选择理论正是以这样的方式保护着我们，这也有助于理解为什么我们都如此相似。进化不会使你变得过于独特，你无论如何不会成为新的物种。

The 0.1 percent difference between your genes and mine is accounted for by our Snips. Now if you compared your DNA with a third person's, there would also be 99.9 percent correspondence, but the Snips would, for the most part, be in different places. Add more people to the comparison and you will get yet more Snips in yet more places. For every one of your 3.2 billion bases, somewhere on the planet there will be a person, or group of persons, with different coding in that position. So not only is it wrong to refer to "the" human genome, but in a sense we don't even have "a" human genome. We have six billion of them. We are all 99.9 percent the same, but equally, in the words of the biochemist David Cox, "you could say all humans share nothing, and that would be correct, too."

你和我的千分之一的基因差异是由我们的Snips决定的。如果将你的DNA与第三个人相比，有99.9%也是一致的，但是你们的Snips在很大程度上会在不同的位置。如果与更多的人相比，你们更多的Snips会在更多的不同的位置。对于你的32亿个碱基中的每个碱基，地球上某个地方某个人或某群人，他或他们在那个位置上的密码会是不同的。因此，不仅“那个”人类基因组这种说法是错误的，在某种意义上我们甚至根本就没有“一个”人类基因组。我们有60亿个基因组，尽管我们的99.9%全都是一样的。但是，同样可以说，正如戴维·考克斯所指出的，”你可以说所有的人没有任何共同之处，这种说法也没错”。

But we have still to explain why so little of that DNA has any discernible purpose. It starts to get a little unnerving, but it does really seem that the purpose of life is to perpetuate DNA. The 97 percent of our DNA commonly called junk is largely made up of clumps of letters that, in Ridley's words, "exist for the pure and simple reason that they are good at getting themselves duplicated."

但是，我们仍然不得不解释，为什么DNA中的绝大部分都没有任何明显的目的。答案乍一看上去有些令人失望，但是生命的目的似乎确实就是使DNA得以永久存在。我们DNA的97%通常被称为垃圾（Junk），它们在很大程度上由字母块组成，用马特·里德利的话说，它们“存在的理由极其单纯和明了，就是因为它们善于复制自己”。