人类的非洲祖先如何走遍世界？DNA研究揭秘

How We Got Here: DNA Points to a Single Migration From Africa

MatterBy CARL ZIMMERSeptember 22, 2016

人类的非洲祖先如何走遍世界？DNA研究揭秘

科学CARL ZIMMER2016年9月22日

Eric Laforgue/Gamma-Rapho,

上百种土著人的基因构成为人类起源提供了新线索，生活在南部非洲的狩猎-采集部落科伊桑人也是其中之一。

Modern humans evolved somewhere in Africa roughly 200,000 years ago. But how did our species go on to populate the rest of the globe?

晚期智人是在大约20万年前，在非洲某处进化而来的。但是我们这个物种又是怎样遍及世界其他地方的呢？

Did humans flood out of Africa in a single diaspora, or did we trickle from the continent in waves spread out over tens of thousands of years? The question, one of the biggest in human evolution, has plagued scientists for decades.

人类是在一次大移居中涌出非洲，还是在几万年的时间里一波一波地离开那片大陆的？这是人类进化中最大的问题之一，它已经困扰了科学家数十年之久。

Now they may have found an answer.

现在他们可能找到了答案。

In a series of unprecedented genetic analyses published on Wednesday in the journal Nature, three separate teams of researchers conclude that all non-Africans today trace their ancestry to a single population emerging from Africa between 50,000 and 80,000 years ago.

星期三，《自然》(Nature)杂志发表了一系列前所未有的基因分析报告，三个不同研究团队都得出结论，非洲之外所有人类的祖先都可以追溯到5万年到8万年前离开非洲的一批人。

Preben Hjort/Mayday Film

奥布雷·林奇是澳大利亚Wongatha土著人群体中的一位老人，他参加了一项基因分析研究，该研究或许有助于揭示古代人类的迁徙。

“I think all three studies are basically saying the same thing,” said Joshua M. Akey of the University of Washington, who wrote a commentary accompanying the new work. “We know there were multiple dispersals out of Africa, but we can trace our ancestry back to a single one.”

“我觉得三组研究基本上说的都是同一件事，”华盛顿大学的约书亚·M·阿基(Joshua M. Akey)说，他为这个新研究撰写了一篇解释性文章。“我们知道，非洲有多次向外界传播人口，但现在我们可以追溯自己的祖先，把他们归结到同一个来源。”

The three teams sequenced the genomes of 787 people, obtaining highly detailed scans of each. The genomes were drawn from people in hundreds of indigenous populations around the world — Basques, African pygmies, Mayans, Bedouins, Sherpas and Cree Indians, to name just a few.

这三个团队为787人做了基因组测序，获取了每个人极为详细的基因组扫描结果。这些基因组来自全世界数百个土著族群，其中包括巴斯克人、非洲俾格米人、玛雅人、贝都因人、夏尔巴人和克里印第安人等等。

The DNA of older indigenous populations may be essential to understanding human history, many geneticists believe. Yet until now scientists have sequenced few whole genomes from people outside population centers like Europe and China. The new findings already are altering scientific understanding of what human DNA looks like, experts said, adding a rich diversity of variation to our map of the genome.

很多遗传学家都认为，较为古老的土著族群的DNA可能对了解人类历史来说更为重要。然而直到如今，科学家才开始为欧洲和中国等人口核心区域之外的少数人做完整的基因组测序。专家们说，新的发现将改变对人类DNA样貌的科学观点，为我们的基因组地图增添丰富的种类。

Each team of researchers used sets of genomes to tackle different questions about our origins, such as how people spread across Africa and how others populated Australia. But all aimed to settle the question of human expansion from Africa.

每个小组的研究者都使用若干基因组，去研究关于人类起源的不同问题，比如人类如何穿越非洲，另一些人又是如何去往澳大利亚。但是他们的目的都是解决人类离开非洲、向外扩张的问题。

In the 1980s, a group of paleoanthropologists and geneticists began championing a hypothesis that modern humans emerged only once from Africa, roughly 50,000 years ago. Skeletons and tools discovered at archaeological sites clearly indicated the existence of modern humans in Europe, Asia and Australia.

20世纪80年代，一组古人类学家与遗传学家开始提出这样一个假设，晚期智人大约是在5万年前一次性离开非洲的。考古地点发现的人类骨骼与工具清楚地表明晚期智人在欧洲、亚洲与澳大利亚洲的存在。

Early studies of bits of DNA also supported this scenario. All non-Africans are closely related to one another, the studies found, and they all branch from a genetic tree rooted in Africa.

早期DNA片段研究也支持这一观点。这些研究表明，非洲以外的所有人类彼此密切相连，而且它们都属于一棵植根于非洲的基因树上的分支。

Yet there are also clues that at least some modern humans lived outside Africa well before 50,000 years ago, perhaps part of an earlier wave of migration.

然而也有证据表明，至少有些晚期智人在5万年前就已经生活在非洲之外，他们或许是在一批较早的移民潮中离开的。

In 2011 Eske Willerslev, a renowned geneticist at the University of Copenhagen, and his colleagues reported evidence that some living people descended from this early wave.

2011年，哥本哈根大学著名遗传学家埃斯克·韦勒斯勒夫(Eske Willerslev)和同事们发现，有证据表明有些现代人是这批早期移民潮的后裔。

Willerslev and his colleagues reconstructed the genome of an aboriginal Australian from a century-old lock of hair kept in a museum — the first reconstruction of its kind. The DNA held a number of peculiar variants not found in Europeans or Asians.

韦勒斯勒夫和他的同事们使用一家博物馆保存的一缕有百年历史的头发，重建了一位澳大利亚土著人的基因组——这是其基因组的首次重建。DNA显示出若干特殊的变体，是欧洲人和亚洲人当中所没有的。

He concluded that the ancestors of Aboriginals spit off from other non-Africans and moved eastward, eventually arriving in East Asia 62,000-75,000 years ago. Tens of thousands of years later, a separate population of Africans spread into Europe and Asia.

他总结说，这位澳大利亚土著人的祖先是来自另一群非洲以外的人，他们向东方迁移，大约在6.2万到7.5万年前来到东亚。数万年后，另一群独立的非洲人在亚洲与欧洲扩展开来。

It was big conclusion to draw from a single fragile genome, so Willerslev decided to contact living Aboriginals to see if they would participate in a new genetic study. He joined David W. Lambert, a geneticist at Griffith University in Australia, who was already meeting with aboriginal communities about beginning such a study.

仅凭一份脆弱的基因序列很难得出这样重大的结论，所以韦勒斯勒夫决定联络尚健在的澳大利亚土著人，看他们是否愿意参与新的基因研究。澳大利亚格里菲斯大学的遗传学家大卫·W·兰伯特(David W. Lambert)也加入进来，他已经和若干土著人社区会面，商讨进行类似研究。

Their new paper also includes DNA from people in Papua New Guinea, thanks to a collaboration with scientists at the University of Oxford. All told, the scientists were able to sequence 83 genomes from aboriginal Australians and 25 from people in Papua New Guinea, all with far greater accuracy than in Willerslev’s 2011 study.

他们的最新论文也包括了来自巴布亚新几内亚人的DNA研究，这是同牛津大学科学家的合作成果。总的来说，科学家们可以为澳大利亚土著人的83个基因组，以及巴布亚新几内亚人的25个基因组进行测序，而且都比韦勒斯勒夫2011年的研究准确很多。

Meanwhile, Mait Metspalu of the Estonian Biocentre was leading a team of 98 scientists on another genome-gathering project. They picked out 148 populations to sample, mostly in Europe and Asia, with a few genomes from Africa and Australia. They sequenced 483 genomes at high resolution.

与此同时，爱沙尼亚生物中心(Estonian Biocentre)的迈特·麦特斯帕卢(Mait Metspalu)领导着一个由98名科学家组成的团队，进行另一项基因组收集工作。他们找来了148个族群作为样本，大都来自欧洲和亚洲，也有一些基因组来自非洲和澳洲。他们以高解析度为483个基因组做了基因测序。

David Reich, a geneticist at Harvard Medical School, and his colleagues assembled a third database of genomes from all five continents. The Simons Genome Diversity Project, sponsored by the Simons Foundation and the National Science Foundation, contains 300 high-quality genomes from 142 populations.

哈佛医学院遗传学家戴维·赖希(David Reich)及其同事们从五大洲收集了第三个基因组数据库。西蒙斯基因组多样性计划(The Simons Genome Diversity Project)由西蒙斯基金会(Simons Foundation)与国家科学基金会(National Science Foundation)赞助，它从142个族群中获取了300个高质量的基因组。

Reich and his colleagues probed their data for the oldest evidence of human groups genetically separating from one another. They found that the ancestors of the KhoiSan, hunter-gatherers living today in southern Africa, began to split off from other living humans about 200,000 years ago and were fully isolated by 100,000 years ago.

为了研究人类群体基因分离的最古老证据，赖希和同事们对这些数据进行了研究。他们发现，至今在非洲南部生活的狩猎-采集部落科伊桑人(KhoiSan)是在大约20万年前从其他人类当中分离出去的，自从10万年前就与其他种群完全隔离。

Earlier studies had estimated that the split between living groups of humans occurred much more recently. The new findings indicate that our ancestors already had evolved behaviors seen in living humans, such as language, 200,000 years ago.

早期研究认为，人类生活群体的分裂是在更近期的时间发生的。新发现表明，20万年前，我们的祖先已经发展出现代人类所拥有的若干行为，比如语言。

Metspalu and his colleagues ended up with a somewhat different result when they looked at the Estonian Biocentre data. They compared chunks of DNA from different genomes to see how long ago people inherited them from a common ancestor.

麦特斯帕卢和同事们对爱沙尼亚生物中心的数据进行了研究之后，得出了一个有些不同的结果。他们对比了不同基因组的大量DNA，旨在研究人类是在多早以前从一个共同祖先那里继承来这些DNA的。

Almost all the DNA from non-Africans today could be traced back to one population that lived about 75,000 years ago — presumably a group of Africans who eventually left the continent and settled the rest of the world. That squares with the conclusions of the other two studies.

几乎所有如今非洲以外人群的DNA都可以追溯到一个7.5万年前的种群——大概是一群非洲人，他们逐渐离开非洲，定居到世界上的其他地方。这同另外两组科学家的研究结论相吻合。

But in Papua New Guinea, Metspalu and his colleagues found, the story was a little different. They could trace 98 percent of each person’s DNA to that 75,000-year-old group. But the other 2 percent was much older.

但在巴布亚新几内亚，麦特斯帕卢和同事们发现，事情有些不太一样。所有人的DNA中的98%都可以追溯到7.5万年前的那群人，但还有2%的DNA更加古老。

Some people in Papua New Guinea — but no one else in the analyses — may carry a trace of DNA from a much older wave of Africans who left the continent as long as 140,000 years ago, and then vanished.

有些巴布亚新几内亚人——但在这项研究中的其他族群中完全没有——可能携带了更早一批离开非洲的人群的DNA，他们可能是在14万年前离开非洲的，之后就销声匿迹。

The second wave — the one from which the rest of the world descends — departed over 60,000 years later, the researchers suggest. The ancestors of the people of Papua New Guinea interbred with those first pioneers on their way east, which is why their descendants carry remarkable DNA.

研究者们认为，第二批离开非洲的浪潮——也就是产生了整个世界其余人口的那一批——发生在大约6万年后。巴布亚新几内亚人的祖先与这一批向东迁徙的人当中的先驱们杂交，所以他们的后代携带了与众不同的DNA。

Why leave Africa at all? Scientists have found some clues as to that mystery, too.

这些人到底为什么离开非洲？科学家们也发现了一些解开这个谜团的线索。

In a fourth paper in Nature, researchers described a computer model of Earth’s recent climatic and ecological history. It shows that changing rainfall patterns periodically opened up corridors from Africa into Eurasia that humans may have followed in search of food.

在《自然》杂志的第四篇论文中，研究者们描述了一个地球近期气候与生态历史的电脑模型。它表明，降雨方式的周期性改变为非洲人打开了进入欧亚大陆的通道，为了觅食，他们沿着这一通路迁徙。