气候越冷人越高大？
Big bodies are good for cold places.
高大的身体有利于在寒冷的地方生存。
That's the gist of a foundational rule in ecology that has been around since the mid-1800s: Animals that live in colder places tend to have larger bodies, especially birds and mammals that need to regulate their body temperatures.
这是自19世纪中期以来生态学中一个基本规则的要点:生活在寒冷地区的动物往往拥有更大的身体，特别是鸟类和哺乳动物，因为需要调节自己的体温。
For example, some of the largest whale and bear species have evolved in the coldest reaches of the planet.
例如，一些最大的鲸类和熊类是在地球上最寒冷的地区进化出来的。
The rule applies broadly to modern humans too.
这一规律总体来说也可以运用在现代人类身上。
Populations that evolved in colder places generally have bigger bodies.
在更寒冷的地方进化的种群一般身材会更高大。
That's also true of human ancestors, a new study finds.
一项新研究发现，对于人类的祖先来说也是如此。
The research offers conclusive evidence that human body size and climate are historically connected.
这项研究提供了确凿的证据，表明人类的体型和气候在历史上是有联系的。
In general, our ancient relatives got much larger as they evolved.
总的来说，我们的远古近亲在进化过程中体型越来越大。
"Over the last million years, you see that body size changes by about 50% and brain size actually triples, which is a lot," explains Andrea Manica, an evolutionary ecologist at the University of Cambridge.
剑桥大学进化生态学家安德里亚·马尼卡解释说:“在过去的一百万年里，你可以看到它们的体型发生了大约50%的变化，而大脑的大小实际上增加了两倍，这是一种很明星的变化。”
"And there have been all sorts of theories about what might have underpinned those two big changes in size."
“关于是什么带来了这两个巨大的尺寸变化，有各种各样的理论。”
Manica and a team of paleontologists and climate scientists in Germany and the United Kingdom set out to test one of those theories: that the local climate was driving brain and body growth.
马尼卡和一个由德国和英国的古生物学家和气候科学家组成的团队开始测试其中一个理论:当地的气候推动了大脑和身体的生长。
They examined about 300 fossils of human ancestors collected in Europe, Asia and Africa, and they used the same basic climate data that scientists use to predict future climate change to estimate instead temperature and precipitation over the last million years.
他们研究了在欧洲、亚洲和非洲收集的约300块人类祖先化石，并使用了科学家用来预测未来气候变化的相同的基本气候数据，来估算过去100万年里的温度和降水。
"We reconstructed climate back in time so we could say what the climate was when that specimen was alive," Manica says.
马尼卡说:“我们重建了那个时代的气候，这样我们就能知道那个标本活着的时候的气候是什么样的。”
The researchers found that human ancestors and Neanderthals living in colder places generally had larger bodies.
研究人员发现，生活在寒冷地区的人类祖先和尼安德特人通常体型更大。
Past studies suggested this might be true but didn't assemble such broad evidence.
过去的研究表明这可能是正确的，但没有收集到如此广泛的证据。
For one thing, past research often relied on rough global estimates of the past climate, whereas this new study estimates what each human ancestor would have experienced in their region.
一方面，过去的研究往往依赖于对过去气候的全球粗略估计，而这项新研究估计了每个人类祖先在其所在地区经历的气候。
The new findings are "reasonably convincing," says Mark Collard, who studies human evolution at Simon Fraser University in Canada and who was not involved in the study.
加拿大西蒙弗雷泽大学研究人类进化的马克·科拉德没有参与这项研究，他说，新发现“相当有说服力”。
However, he suspects that the new analysis may overstate the relationship between temperature and body size because of uncertainties in both the fossil record and the climate data.
然而，他怀疑由于化石记录和气候数据的不确定性，新的分析可能夸大了温度和体型之间的关系。
The authors of the new study also found that the rapid increase in human brain size over the last million years was not strongly correlated with climate.
这项新研究的作者还发现，在过去的一百万年里，人类大脑体积的快速增长与气候并没有太大的关联。
"For brains, you need other explanations," says Manica, perhaps such as diet or social structures.
“对于大脑，你需要其他的解释，”马尼卡说，也许是饮食或社会结构。
For decades, scientists who study human evolution have posited that what our ancestors ate — whether it was cooked or raw, whether it included meat or only vegetables — influenced how our brains evolved.
几十年来，研究人类进化的科学家们一直认为，我们的祖先吃什么——无论是煮熟的还是生的，是吃肉还是只吃蔬菜——影响了我们大脑的进化。
It's also possible that more complex social structures and group communication are linked to brain growth in human ancestors.
更复杂的社会结构和群体交流也可能与人类祖先的大脑发育有关。
"I suspect that social factors such as group size are more likely to influence brain size," Collard says.
“我怀疑像群体大小这样的社会因素更有可能影响大脑的大小，”克拉德说。
Modern humans need not worry that the new findings about body size and climate will show up in our daily lives.
现代人不必担心关于体型和气候的新发现会出现在我们的日常生活中。
The Earth is getting steadily hotter because of human-caused climate change.
由于人为造成的气候变化，地球正变得越来越热。
But human body size will not shrink as a result, at least not in the near future.
但是人类的体型不会因此而缩小，至少在不久的将来不会。
That's because it takes many, many generations for humans to evolve.
那是因为人类需要很多很多代才能进化。
The average human generation is about 30 years, so it would take hundreds or even thousands of years of sustained warming before human body size changed in reaction to global warming.
人类平均一代大约需要30年，所以需要数百年甚至数千年的持续变暖，人类的体型才会因全球变暖而发生变化。
And, even then, the changes would be very slight — about 1 kilogram per 2 degrees of warming, Manica says.
马尼卡说，即使到那时，变化也会非常微小——大约每升高2度就有1公斤的体重变化。
"We're not going to shrink tomorrow," he says. "That's the good news. But climate change is problematic for many other reasons."
他表示:“我们不会明天就缩水。” “这是好消息。 但气候变化还会带来很多其他的问题。”