万物简史 第578期:生命的物质(4)（在线收听）

DNA exists for just one reason — to create more DNA — and you have a lot of it inside you: about six feet of it squeezed into almost every cell. Each length of DNA comprises some 3.2 billion letters of coding, enough to provide 103,480,000,000 possible combinations, "guaranteed to be unique against all conceivable odds," in the words of Christian de Duve. That's a lot of possibility — a one followed by more than three billion zeroes. "It would take more than five thousand average-size books just to print that figure," notes de Duve. Look at yourself in the mirror and reflect upon the fact that you are beholding ten thousand trillion cells, and that almost every one of them holds two yards of densely compacted DNA, and you begin to appreciate just how much of this stuff you carry around with you. If all your DNA were woven into a single fine strand, there would be enough of it to stretch from the Earth to the Moon and back not once or twice but again and again. Altogether, according to one calculation, you may have as much as twenty million kilometers of DNA bundled up inside you.

DNA存在的原因只有一个——生成更多的DNA——你的身体内有很多DNA：将近2米长的DNA挤在差不多每个细胞里。每单位长度的DNA包括32亿个密码字母，足以产生103480000000种组合，用克里斯琴·德迪夫的话说，“无论如何可以确保独一无二的地位”。这个概率很大——1的后面加上30多亿个零，“光是印刷这些数字，就要用5000本一般大小的书。”德迪夫解释说。仔细端详镜子中的你自己，想一想这样一个事实，你含有1亿亿个细胞，几乎每一个细胞又都包含约2米长的挤成一团的DNA，你就会意识到你身上有多少这种东西。如果将你身上所有的DNA连成一条细线，它的长度不是地球到月球距离的一个或两个来回，而是好几个来回。根据一种统计，你身上的DNA总长度达2000万公里。

Your body, in short, loves to make DNA and without it you couldn't live. Yet DNA is not itself alive. No molecule is, but DNA is, as it were, especially unalive. It is "among the most nonreactive, chemically inert molecules in the living world," in the words of the geneticist Richard Lewontin.

一句话，你的身体喜欢制造DNA，没有它你就不能生存。然而DNA本身并没有生命。分子也没有生命，但DNA可以说是尤其没有生命。用遗传学家理查德·莱旺顿的话来说，它是“生命世界中最非电抗性的化学惰性分子”。