1、 普特英语听力 免费学习英语更多下载 Americans Heads Are Getting Bigger美国人的头越来越大了！The story of human evolution goes something like this: Millions of years ago, homo sapiens began to evolve from the prehistoric ancestor we share with our monkey cousins. First, we evolved the ability to walk upright. Then we began fabr
2、icating more elaborate tools. Finally, around 50,000 years ago, we emerged as more or less fully modern humans with large, fully human brains. And since then, our craniums and the brains they harbor have stayed pretty much the same.Except that, according to one study, the skulls of some Americans ha
3、ve actually grown over the past 120 or so years. Specifically, skulls have become larger by about eight millimeters, or a third of an inch. Which may not sound like much, but the growth theoretically allows for additional brain matter roughly equivalent to the size of a tennis ball.Now, before we go
4、 any further, we need to deal with a tricky detail of the study, namely, that the researchers looked almost exclusively at skeletons of white Americans. Why? Because, historically, mainly white Americans had donated skeletons to the collections the researchers studied. So while it may be the case th
5、at the skulls of Americans of many ethnicities have grown, the study provides evidence only for one group.In any case, its not at all clear that larger skulls have translated to larger brains or to greater intellect. Its also not clear why the skulls the researchers looked at got bigger. American li
6、fe has changed so much over the past century and a half that it will take years of research to begin to identify possible causes.But, nevertheless, the observation is interesting as another detail in the complex story of human evolution.人类进化的过程大概是这样：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。最初，我们进化到能够直立行走。然后，我们开始制
7、造更为复杂的工具。最终，大约在五万年前，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。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。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。具体说来，颅骨增大了约八毫米或三分之一英寸。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。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，也就是：研究者几乎排除性地只观察了美国白人的骨骼。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。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。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。并且，研究普特英语听力 免费学习英语更多下载 人员所观察的颅骨增大的原因也仍不清楚。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。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。
