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The story of human evolution goes something like this:
人類進化的過程大概是這樣：
Millionsof years ago, homo sapiens began to evolve from the prehistoric ancestor we share with ourmonkey cousins.
數百萬年以前，我們和猿類共同的史前祖先開始進化成智人。
First, we evolved the ability to walk upright.
最初，我們進化到能夠直立行走。
Then we began fabricating moreelaborate tools.
然后，我們開始制造更為復雜的工具。
Finally, around 50,000 years ago,
最終，大約在五萬年前，
we emerged as more or less fully modernhumans with large, fully human brains.
人類以與現代人差不多的樣子出現了，擁有大而完全的人類大腦。
And since then, our craniums and the brains they harborhave stayed pretty much the same.
自那時起，我們的頭蓋骨以及它所保護的腦部幾乎保持不變。
Except that, according to one study, the skulls of some Americans have actually grown over thepast 120 or so years.
除此以外，一項研究稱在過去的一百二十多年的時間里一部分美國人的顱骨確實增長了。
Specifically, skulls have become larger by about eight millimeters, or a thirdof an inch.
具體說來，顱骨增大了約八毫米或三分之一英寸。
Which may not sound like much, but the growth theoretically allows for additional brainmatter roughly equivalent to the size of a tennis ball.
聽起來似乎不多，但這個增長理論上能容下差不多相當于一個網球大小的額外的腦容量。
Now, before we go any further, we need to deal with a tricky detail of the study,
現在，在我們繼續分析之前，我們需要關注這項研究中的一個棘手的問題，
namely, that theresearchers looked almost exclusively at skeletons of white Americans.
也就是：研究者幾乎排除性地只觀察了美國白人的骨骼。
Why? Because, historically,mainly white Americans had donated skeletons to the collections the researchers studied.
為什么？這是源于歷史上主要是 美國白人向研究人員捐獻了骨骼以供研究之用。
So whileit may be the case that the skulls of Americans of many ethnicities have grown, the studyprovides evidence only for one group.
因此，雖然由多種族組成的美國人的顱骨可能都在增大，但這份研究僅提供了其中一個群體頭顱增大的證據。
In any case, it's not at all clear that larger skulls have translated to larger brains or to greaterintellect.
何況，更大的顱骨是否意味著更大的腦部以及更高的智慧，這仍是未知之數。
It's also not clear why the skulls the researchers looked at got bigger.
并且，研究人員所觀察的顱骨增大的原因也仍不清楚。
American life haschanged so much over the past century and a half that it will take years of research to begin toidentify possible causes.
美國人的生活在過去的一個半世紀發生了如此巨大的變化以至于我們需要多年的研究方能確定可能的原因。
But, nevertheless, the observation is interesting as another detail in the complex story of humanevolution.
但是，盡管如此，作為人類復雜的進化史上的一個新的發現，這項觀察結果還是很有意思的。
