The story of human evolution goes something like this:
人类进化的过程大概是这样：
Millionsof years ago, homo sapiens began to evolve from the prehistoric ancestor we share with ourmonkey cousins.
数百万年以前，我们和猿类共同的史前祖先开始进化成智人。
First, we evolved the ability to walk upright.
最初，我们进化到能够直立行走。
Then we began fabricating moreelaborate tools.
然后，我们开始制造更为复杂的工具。
Finally, around 50,000 years ago,
最终，大约在五万年前，
we emerged as more or less fully modernhumans with large, fully human brains.
人类以与现代人差不多的样子出现了，拥有大而完全的人类大脑。
And since then, our craniums and the brains they harborhave stayed pretty much the same.
自那时起，我们的头盖骨以及它所保护的脑部几乎保持不变。
Except that, according to one study, the skulls of some Americans have actually grown over thepast 120 or so years.
除此以外，一项研究称在过去的一百二十多年的时间里一部分美国人的颅骨确实增长了。
Specifically, skulls have become larger by about eight millimeters, or a thirdof an inch.
具体说来，颅骨增大了约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.
听起来似乎不多，但这个增长理论上能容下差不多相当于一个网球大小的额外的脑容量。
Now, before we go any further, we need to deal with a tricky detail of the study,
现在，在我们继续分析之前，我们需要关注这项研究中的一个棘手的问题，
namely, that theresearchers looked almost exclusively at skeletons of white Americans.
也就是：研究者几乎排除性地只观察了美国白人的骨骼。
Why? Because, historically,mainly white Americans had donated skeletons to the collections the researchers studied.
为什么？这是源于历史上主要是 美国白人向研究人员捐献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，虽然由多种族组成的美国人的颅骨可能都在增大，但这份研究仅提供了其中一个群体头颅增大的证据。
In any case, it's not at all clear that larger skulls have translated to larger brains or to greaterintellect.
何况，更大的颅骨是否意味着更大的脑部以及更高的智慧，这仍是未知之数。
It's also not clear why the skulls the researchers looked at got bigger.
并且，研究人员所观察的颅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.
美国人的生活在过去的一个半世纪发生了如此巨大的变化以至于我们需要多年的研究方能确定可能的原因。
But, nevertheless, the observation is interesting as another detail in the complex story of humanevolution.
但是，尽管如此，作为人类复杂的进化史上的一个新的发现，这项观察结果还是很有意思的。
