In 1997, scientists found the first scrap of Neanderthal DNA in a fossil. Since then, they have recovered genetic material, even entire genomes, from a number of Neanderthal bones, and their investigations have yielded a remarkable surprise: Today, 1 to 2 percent of the DNA in non-African people comes from Neanderthals.1997年，科学家在化石中第一次找到了尼安德特人DNA的碎片。此后，他们从相继发掘出的多块尼安德特人的骨头中萃取了基因物质，乃至原始的基因组。

他们的研究进账了一个难以置信的找到：今天，在除了非洲人之外的人类身上，有1%到2%的DNA来自尼安德特人。That genetic legacy is the result of interbreeding roughly 50,000 years ago between Neanderthals and the common ancestors of Europeans and Asians. Recent studies suggest that Neanderthal genes even influence human health today, contributing to conditions from allergies to depression.这份基因遗产，是约5万年前尼安德特人和欧亚人的联合祖先混种交配的结果。近期的研究指出，尼安德特人的基因甚至影响到当今人类的身体健康，与还包括过敏和抑郁症在内的多个病状有关。

Now scientists have found that the genes flowed both ways. In a study published on Wednesday in Nature, a team of scientists reports that another instance of interbreeding left Neanderthals in Siberia with chunks of human DNA.如今，科学家找到基因的流动是双向的。在《大自然》杂志(Nature)周三公布的一篇研究论文中，一组科学家递交的案例指出，混种交配使得西伯利亚的尼安德特人具有部分人类DNA。This exchange, the scientists conclude, took place about 100,000 years ago. That’s a puzzling date, because a great deal of evidence indicates that the ancestors of today’s non-Africans did not expand out of Africa until 50,000 to 60,000 years ago.这群科学家得出结论，这种交融再次发生在大约10万年前。

这一日期令人困惑，因为大量证据表明，直到5万到6万年前，如今不出非洲的人类的祖先才走进了非洲大陆。It’s possible, then, that these Neanderthals acquired DNA from a mysterious early migration of humans.那么，这些尼安德特人有可能就是指一群早期的谜样人类迁移群体身上取得了DNA。

“I think at this point we’ve convinced everybody the observation is real,” said Adam Siepel, a geneticist at Cold Spring Harbor Laboratory and a co-author of the new study. “But the story behind the observation is still very much in dispute.”“我指出，现在我们早已让所有人信服，我们的观测结果是现实的，”来自美国冷泉港实验室(Cold Spring Harbor Laboratory)的遗传学家亚当·西佩尔(Adam Siepel)回应。他是这项新的研究的联合作者。“但观测结果背后的说明，仍然争议重重。

”Humans and Neanderthals split from a common ancestor in Africa about 600,000 years ago. At some point afterward, the ancestors of Neanderthals spread to Europe, the Middle East and Central Asia.在约60万年前，享有非洲联合祖先的人类和尼安德特人分道扬镳。此后的某个时刻，尼安德特人的祖先蔓延到欧洲、中东和中亚地区。

Along the way, Neanderthals took on a distinctive anatomy — a stocky, powerful build — and became impressive hunters of big game. The last Neanderthals appear to have died about 40,000 years ago.迁移途中，尼安德特人演化出矮壮而有力的独有体型，并沦为狩猎大型动物的佼佼者。最后一代尼安德特人或许在约4万年前覆灭。In 2010, scientists at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, recovered about 60 percent of a Neanderthal genome from fossils found in a Croatian cave. Neanderthals shared certain mutations with living Europeans and Asians, the scientists found — but not with modern Africans. They concluded that humans must have interbred with Neanderthals after leaving Africa.2010年，德国莱比锡马克斯·普朗克进化人类学研究所(Max Planck Institute for Evolutionary Anthropology)萃取了尼安德特人的一个约60%的基因组，所用样本来自克罗地亚一处洞穴中发掘出的化石。

科学家找到，尼安德特人和如今的欧亚人分享一定的基因突变，但与现代非洲人并无共通之处。科学家得出结论，人类一定是在离开了非洲大陆后和尼安德特人展开了混种交配。Three years later, the Max Planck team reconstructed the complete genome of a male Neanderthal from a toe bone dating back at least 50,000 years, which had been discovered in the Altai Mountains of Siberia. Comparing the Altai genome to modern human DNA confirmed the interbreeding.三年后，马克斯·普朗克的研究团队重构了一名男性尼安德特人的原始基因组。

这些基因来自西伯利亚阿尔泰山脉考古的一块距今最少5万年的趾骨。通过较为阿尔泰山脉尼安德特人的基因组和现代人类的DNA，证实了混种交配的不存在。

Recently, the researchers harvested more DNA from European Neanderthal fossils, putting together very detailed reconstructions of a single chromosome, Chromosome 21.近期，研究者从欧洲尼安德特人化石上进账了更好DNA信息，重构出有十分详细的单条染色体——第21号染色体。Sergi Castellano, a geneticist at Max Planck Institute, set out to compare this European Neanderthal DNA to the genes from Siberia. He was curious about how isolated the populations of Neanderthals were from one another, and how they were related to humans alive today.马克斯·普朗克研究所的遗传学家塞尔吉·卡斯特利亚诺(Sergi Castellano)著手较为了欧洲尼安德特人的DNA和西伯利亚尼安德特人的基因。

让他感兴趣的是，尼安德特人群体互相隔绝的程度，以及他们与当今人类的关联。He was joined by Dr. Siepel, who has developed powerful statistical models in recent years to trace how DNA changes over time. He and his colleagues are able to compare genomes and infer their common history: how their ancestors split apart, for example, and how large the populations of their ancestors were.他邀了西佩尔博士重新加入。

在过去数年里，西佩尔建构出有强劲的统计学模型来跟踪DNA如何随时间而进化。于是，他和同事需要较为这些基因组，推测他们联合的历史：比如，他们的祖先是如何分化的，祖先的人口规模又有多大。

Dr. Siepel, Dr. Castellano and their colleagues used these models to analyze the Neanderthal DNA and that of humans. Their analysis confirmed previous studies: Some Neanderthal DNA did indeed end up in modern Europeans and Asians.西佩尔、卡斯特利亚诺及同事利用这些模型分析了尼安德特人和人类的DNA。他们的分析结果证实了之前的研究：尼安德特人的DNA片段的确经常出现在了现代欧亚人的身上。But they also found another example of so-called gene flow, and an unexpected one at that: The Altai Neanderthals in particular shared some mutations with living Africans, but not with Europeans and Asians.不过，他们还找到了“基因流动”的又一个例子，而且是个出人意料的例子：具体来说，是阿尔泰山脉的尼安德特人与今天的非洲人有一些某种程度的变异，而不是欧亚人。

That pattern suggests that an African lineage of humans interbred with the ancestors of the Altai Neanderthal after they split from other Neanderthals.这意味著，有一支非洲人类，在阿尔泰山脉尼安德特人的祖先与其他尼安德特人分离之后，与其展开过混种交配。Dr. Castellano and Dr. Siepel thought at first there was something wrong with their analysis, so they went back to fix it. But when they looked for the problem, they could not find it.卡斯特利亚诺和西佩尔最初以为是自己的分析出有了错，于是走去修正。

但他们却没寻找问题。“We poked and prodded and poked and prodded, and couldn’t get it to go away,” said Dr. Siepel.“我们这里想到，那里瞧瞧，就是没办法让它消失，”西佩尔说道。Once the scientists accepted that the interbreeding was real, they estimated when it happened. When DNA gets passed down through the generations, it gets shuffled into new arrangements that can be used to build a sort of timeline.一旦科学家们拒绝接受了混种交配的情况现实不存在，他们就开始估计它再次发生的时间。

DNA在代际遗传的时候，不会展开重组，而这就可以用来创建某种时间表。Based on this gene shuffling, the scientists estimated that humans and the ancestors of the Altai Neanderthals interbred about 100,000 years ago — long before people were thought to have left Africa. “This observation throws a wrench in the works,” said Dr. Siepel.基于这种基因重组，科学家们估计出有，人类与阿尔泰山脉尼安德特人的祖先在约10万年前展开过混种交配——远在普遍认为的人类离开了非洲的时间之前。

“这一观测结果给我们的工作造成了相当大的困难，”西佩尔说道。Bence Viola, a paleontologist at the University of Toronto and a co-author of the new study, said he was skeptical when he first learned of the genetic data. “It’s really weird, that’s my main impression,” he said.同为这项新的研究作者的多伦多大学(University of Toronto)古生物学家本斯·维奥拉(Bence Viola)回应，刚刚听见这些基因数据的消息时，他本人满腹狐疑。“觉得是怪异，这就是我的主要印象，”他说道。Eventually, however, Dr. Castellano persuaded him the data were strong, and Dr. Viola looked over the fossil record for possible explanations for the interbreeding.不过，卡斯特利亚诺最后劝说他坚信数据是可信的。

于是维奥拉博士查阅了也许可以说明这一混种交配的化石记录。In the 1930s, for example, scientists discovered 120,000-year-old fossils in Israel that looked a lot like living humans. Many scientists viewed them as a failed human migration from Africa, with no genetic connection to humanity today.比方说，上世纪30年代，科学家们在以色列找到了一批12万年前的化石，与现代人类有诸多相似之处。

许多科学家指出，它们代表了人类走进非洲的一次告终尝试，与今天的人类没基因联系。In October, Chinese researchers discovered another intriguing clue in a cave: 47 teeth that they estimate are between 80,000 and 120,000 years old. The scientists argue that the teeth belonged to modern humans.去年10月，中国研究者在一处洞穴找到了另一个有意思的线索：47颗牙齿。这些科学家估计牙齿有8到12万年历史，并明确提出它们归属于现代人类。

Dr. Viola is not completely convinced by the Chinese study. Instead, he thinks the scenario that best fits the evidence is that humans expanding into the Middle East encountered and interbred with Neanderthals there. The Neanderthals then migrated east to Siberia, taking human DNA with them.中国科学家的研究未几乎劝说维奥拉。他指出，能与证据相符得最差的情景是，蔓延到中东地区的人类与当地的尼安德特人展开了混种交配。然后尼安德特人东迁到西伯利亚地区，身上带着人类的DNA。

“It seems pretty solid,” said Jonathan K. Pritchard, a geneticist at Stanford University who was not involved in the study. “Overall, the story they’re telling is pretty coherent.”“看上去很有说服力，”没参予这项研究的斯坦福大学(Stanford University)遗传学家乔纳森·K·弗里查德(Jonathan K. Pritchard)这样评价道。“总体而言，他们明确提出的这套说词较为条理分明。”Dr. Pritchard said that more examinations of ancient DNA would help resolve the many questions raised by the new study and help scientists understand the scope of the intimate back-and-forth between Neanderthals and humans.弗里查德博士回应，对古DNA的更好研究将有助答案这项新的研究明确提出的许多问题，并协助科学家解读尼安德特人与人类之间亲近的互相往来的范围。

“There’s going to be a lot more data really soon,” he said. “I would expect in the next few years we’ll have much, much more of the jigsaw puzzle, and it will be possible to piece this all together.”“迅速就不会经常出现许许多多的新数据，”他说道。“我指出，在接下来的几年里，不会有非常少的碎片冒出来，也就有可能把它们都拼凑一起。

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