万物简史 第356期:孤独的行星(21)（在线收听） |
We have evolved to utilize or tolerate these things—we could hardly be here otherwise— but even then we live within narrow ranges of acceptance. 我们已经逐步学会利用或忍受这些东西——要不然我们几乎不可能在这里——但即使那样，我们所能忍受的范围也很窄。 Selenium is vital to all of us, but take in just a little too much and it will be the last thing you ever do. 硒对我们大家都是至关重要的，但只要摄入一丁点儿，你就会呜呼哀哉。
The degree to which organisms require or tolerate certain elements is a relic of their evolution. 生物对某些元素的要求或耐受性是它们进化的结果。
Sheep and cattle now graze side by side, but actually have very different mineral requirements. 现在羊和牛在一起吃草，实际上它们所要求的矿物质非常不同。
Modern cattle need quite a lot of copper because they evolved in parts of Europe and Africa where copper was abundant. 现代的牛需要大量的铜，因为它们是在铜很丰富的欧洲和非洲地区进化的。
Sheep, on the other hand, evolved in copper-poor areas of Asia Minor. 而羊是在铜很缺乏的小亚细亚进化的。
As a rule, and not surprisingly, our tolerance for elements is directly proportionate to their abundance in the Earth's crust. 一般来说，我们对元素的耐受力与那些元素在地壳里德丰度成正比，这是不足为怪的。
We have evolved to expect, and in some cases actually need, the tiny amounts of rare elements that accumulate in the flesh or fiber that we eat. 我们已经进化到这种程度，希望——在有些情况下其实需要——在我们所吃的肉类或纤维里积累着少量的稀有元素。
But step up the doses, in some cases by only a tiny amount, and we can soon cross a threshold. 但是，要是加大剂量，在有的情况下就加大一丁点儿，我们可能会很快去另一个世界。
Much of this is only imperfectly understood. 这类知识在很大程度上我们还是一知半解。
No one knows, for example, whether a tiny amount of arsenic is necessary for our well-being or not. 比如，谁也说不清，摄入一丁点儿砷对我们的健康到底是有益的还是有害的。
Some authorities say it is; some not. 有的权威说有益，有的权威说有害。
All that is certain is that too much of it will kill you. 只有一点是肯定的，摄入太多，你就会送命。
The properties of the elements can become more curious still when they are combined. 元素一旦化合，它们的性质会变得更加奇特。
Oxygen and hydrogen, for instance, are two of the most combustion-friendly elements around, but put them together and they make incombustible water. 比如，氧和氢是两种最易燃的元素，但要是结合在一起，就变成了不易燃的水。 |
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