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You may have heard that humans and chimpanzees have something like 96 percent of our DNA² in common. So why, then, are diseases like cancer so common in humans but so rare in chimps³? If our DNA is nearly identical, shouldn’t we be at risk for many of the same diseases?
你也许会听说人类和黑猩猩约有96%的DNA相同。那么，为什么人类常常患有比如癌症这样的疾病，而在黑猩猩极少呢？如果我们和猩猩的DNA近乎相同，为何在面对许多相同的疾病时，我们和猩猩的患病率不同呢？

According to one study, the difference is due to something called DNA methylation, which involves the chemical modification⁴ of DNA. Basically, methylation modifies some DNA positions in the genome, and can also signal cells to switch specific genes⁵ to the “off” position.
根据一份研究，造成这种差异的原因是一种被称为DNA甲基化的物质，它与DNA的化学变化有关。简单来说，甲基化改变了一些DNA在染色体组中的位置，也可以通知细胞把特殊的基因转换到“关闭”的位置。

Evidently, humans and chimps have different patterns of DNA methylation. So even though we may share many of the same genes, the ways our cells switch these common genes on and off differs. And because at least some of these genes are linked to diseases including cancer, variations in the way DNA methylation happens among humans and chimps may help explain why chimps seem to avoid diseases common in humans.
显然，人类和黑猩猩拥有不同的DNA甲基化模式。因此，尽管人类和猩猩有许多相同基因，但是细胞开关这些相同基因的方式是不同的。而且，因为这些基因中至 少有一部分关系到包括癌症在内的各种疾病，所以人类和猩猩体内DNA甲基化发生的方式不同，或许就能用来解释为什么猩猩能抵御人类常患的疾病。

So what explains the differences among human and chimp¹ DNA methylation? It may be partly biological, but scientists also know that environmental factors can affect methylation. So studying methylation in humans and chimps could give scientists clues about how genetics and environment combine to make humans more vulnerable to cancer and other diseases.
那又如何解释人类和猩猩DNA甲基化的不同呢？这或许要牵涉到一部分生物学原理，但是科学家们也认识到环境因素能影响甲基化。因此对人类和猩猩甲基化的研究可能会给于科学家们一些线索，以了解到基因和环境的综合影响是如何使人类更容易患有癌症和其他疾病。