乳糖人类进化

Anthropology 人类学

Notwhattheywere进化的人类亚洲人在成年后乳糖酶活性普遍下降至消失，统计表明泰国约有97%的人乳糖不耐［Lactoseintolerance］，而在丹麦，乳糖不耐者只有3%。畜牧业又是如何伴随人类进化之路发展的？...

Not what they were

进化的人类

Researchers can now watch human evolution unfold

科研者们展开了人类演化的画卷

May 14th 2016 | From the print edition

STUDYING recent human evolution can be frustrating. Take lactose tolerance—the ability of some people, particularly of European descent, to digest this sugar, found in milk, even into adulthood. In the evolutionary past the gene for lactase, the enzyme that does the digesting, normally got switched off in adults. But one variant (known as an allele) of the gene that does the switching off instead leaves the system running, conferring adult lactose tolerance. That lets this allele’s bearers consume a diet rich in dairy products, a useful trick for a species beginning to domesticate milk-producing animals. Genetic analysis shows that lactose tolerance emerged between 5,000 and 10,000 years ago. In evolutionary terms, it is thus extremely recent. In human terms, though, that timescale means how it spread and how this process intertwined with the rise of dairy farming are lost in the mists of prehistory.

研究近年来的人类进化史可能让人很沮丧。就乳糖耐力来说——部分人群，特别是欧洲血统的人，可以到成年后仍保持对乳糖的消化能力。人类进化至今的结果是，成年后人体内的乳糖酶（lactase）活性逐渐下降甚至完全消失。但是有一个变异基因（称为等位基因）代替了乳糖酶的作用并赋予成年人体分解乳糖的能力。而携带该等位基因的人群则养成了驯养产乳动物的饮食习惯。（译者注：亚洲人在成年后乳糖酶活性普遍下降至消失，统计表明泰国约有97%的人乳糖不耐［Lactose intolerance］，而在丹麦，乳糖不耐者只有3%，资料来源于维基百科“https://en.wikipedia.org/wiki/Lactose_intolerance”，统计结果见下图：）遗传分析表明，乳糖耐受能力出现在5,000～10,000年前。从进化的时间尺度来看，这一切的发生仿若昨天。对整个人类而言，该等位基因是如何在这么短的时间内在地球范围内扩散，以及畜牧业如何伴随人类的进化路线，已经成为历史上的一团迷雾，不可捉摸。

It would be nice, therefore, to have a technique that could look at human evolution on a scale of centuries, rather than millennia. And on May 7th a team led by Jonathan Pritchard, a biologist at Stanford University, announced they had come up with one. In a paper posted to bioRxiv, they describe it, and also how they have used it to track ways the inhabitants of Britain have altered over the past 2,000 years.

幸而出现了一项新的技术，它使得我们可以按百年而不是千年为刻度探索人类的进化史。5月7日，斯坦福大学的生物学家 Jonathan Pritchard 带领的一个团队在《bioRxiv》上发表的一篇论文宣称，他们已经拥有了该项技术，并应用该技术研究了英国居民过去2,000年来的演变。

The team’s technique looks for changes not in alleles themselves, but in the DNA that surrounds those alleles. If a particular allele is more beneficial than other variants of a gene, it will tend, as lactose tolerance did, to spread through the population. As it does so, it will carry with it neighbouring DNA which is not strictly part of the gene and does not affect its function. This DNA can thus mutate without damaging the allele. And it is the amount of mutation this peripheral DNA has undergone which is the giveaway. DNA neighbouring an allele that has recently spread quickly will have had less time to accumulate mutations than that near one which evolution has been ignoring. By looking for evidence of mutations around particular alleles, Dr Pritchard and his team can reconstruct their history. Apply the method to lots of people, and it is possible to discern what evolution has been up to.

该技术并未死盯等位基因的变化，而是着重研究了等位基因周围的DNA。研究结果表明，如果一个特定的等位基因较之其他的基因更有益于人体，如“乳糖耐受”有益于人体（译者：随着生活环境的变迁，如畜牧业开始发展），那么进化就会向这个方向发展，并在人群中生效。发生效应的基因会和与它相邻的DNA协作，这些从严格意义上讲并非该基因的一部分的DNA并不会破坏这些等位基因，并会逐渐“接纳”这些等位基因。等位基因的DNA邻居们的快速响应弥补了进化中基因突变的失误并加速了这一进程。通过观察等位基因附近的基因突变的证据，以及大量人群的统计，Pritchard 博士和他的团队再现了人类进化史中的这一过程。

To test their method, the researchers turned to 3,195 genomes taken from the UK10K project, which has collected the genetic data of 10,000 Britons. The largest signal they found did indeed come from the allele for lactose tolerance, suggesting that evolution has continued to press the case for milk digestion well into recorded human history. They also found evidence of strong selection for blond hair and blue eyes. This, they speculate, may be a consequence of the sexual preferences of ancient Britons rather than any environmental influence.

为了验证他们的方法，研究人员参考了UK10K项目中的3195基因组，该项目收集有一万名英国人的基因数据。从中他们发现乳糖耐受确实来自于等位基因，这意味着人类的进化是伴随着牛奶进入人类的饮食习惯而发生的。同时他们发现，金发碧眼人群有较强的选择优势，而这一结果可能更多来自古代英国人的性偏好而非环境影响的结果。

Lactose tolerance and hair- and eye-colour are traits strongly influenced by small numbers of genes. But Dr Pritchard’s method can also detect “polygenic” selection, in which the accumulated effects of thousands of small variants conspire to produce a big change in a particular trait. One example is height, which is influenced by the combined actions of thousands of different genes.

乳糖耐受力和眼睛头发颜色这样的显著差异，都来自于很少量的人类基因的影响。而Pritchard 博士的方法可以检测多基因的进化选择效果。基因片段成千上万的微小变化累积导致生物后来的巨大变化。如身高变化，就是由数千种不同的基因共同作用的效果。

Dr Pritchard and his colleagues found that in Britain evolution has, of late, been extremely keen on taller people. Selection for increased height appears to have taken place across nearly the entire human genome. They also found evidence that other ancient evolutionary pressures still operate in comparatively modern populations. Human babies have big heads to contain their outsized brains. Women, in turn, need wide hips to give safe birth to their big-headed offspring. Genetic variations associated with head circumference in infants, and wider hips in women, seem to have become noticeably more common even over the past couple of millennia.

Pritchard 博士和他的同事们发现，在英国人的进化过程中，直到目前为止，高个子往往更受欢迎。选择增加身高似乎已经成为全部人类基因组共同合作努力的目标。研究同时表明，一些古老的进化压力似乎仍在影响着现代人类的发展。人类婴儿的头部发育的更大以容纳更多脑容量，妇女的骨盆的变的更宽以利于生产。相关基因的变化在过去的几千年中深深影响着人类的变化。

Dr Pritchard’s technique thus adds evolutionary biology to the armoury of archaeological anthropology. His results confirm that modern Britons are subtly but definitely different from those who tried (unsuccessfully) to fight off the Romans. The effects of two thousand years of evolution, covering a hundred or so generations, are such that if ancient Britons were given all the benefits of a modern diet and modern medicine, they would still end up shorter than their modern counterparts, have narrower hips, and give birth to babies with slightly smaller heads.

Pritchard 博士的技术为生物进化学增加了一项新的趁手工具。他的研究结果表明，现代英国人与他们尝试击退罗马人的祖先已经有了细微但明显的变化。两千多年，一百多代人的演变，使得即使是他们的古代祖先拥有了现代的营养和医疗，也不会像现代英国人一样更加长寿。当时英国人的臀部更窄，新生儿的头部更小。

翻译 & 校对：常志平

译者注：谨以此文送给我的喜欢喝牛奶而又经常闹肚子的亲爱的朋友们。改变一下自己的饮食习惯，可能对身体更好，毕竟基因的研究结果、农耕人群的饮食习惯的历史变革比牛奶厂商的广告更具有说服力，王熙凤的奶子粳米粥不一定适用所有的人群，最多可以理解为一种炫富的食疗粥。

From the print edition: Science and technology