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人类原来是个混血物种

更新时间:2016-3-27 9:42:11 来源:纽约时报中文网 作者:佚名

Ancestors of Modern Humans Interbred With Extinct Hominins, Study Finds
人类原来是个混血物种

The ancestors of modern humans interbred with Neanderthals and another extinct line of humans known as the Denisovans at least four times in the course of prehistory, according to an analysis of global genomes published on Thursday in the journal Science.

根据星期二出版的《科学》杂志内的一份全球基因组的分析报告,在远古时期,现代人的祖先同尼安德特人及另一个已灭绝的丹尼索瓦人至少有过4次混种繁衍行为。

The interbreeding may have given modern humans genes that bolstered immunity to pathogens, the authors concluded.

作者推测,这种混种繁衍可能给予现代人类基因强大的免疫能力。

“This is yet another genetic nail in the coffin of our over-simplistic models of human evolution,” said Carles Lalueza-Fox, a research scientist at the Institute of Evolutionary Biology in Barcelona who was not involved in the study.

“这也是另一种遗传学结论,人类进化是极其简单的模式。”巴塞罗那生物进化学院的古遗传学专家卡尔斯·拉鲁斯-福克斯说。他并未参与此项研究。

The new study expands on a series of findings in recent years showing that the ancestors of modern humans once shared the planet with a surprising number of near relatives — lineages like the Neanderthals and Denisovans that became extinct tens of thousands of years ago.

这个最新研究详诉了一系列最近几年的发现,表明现代人类祖先曾经同数量惊人的近亲共同生活在这个星球上——数万年前已经灭绝的尼安德特人和丹尼索瓦人。

Before disappearing, however, they interbred with our forebears on at least several occasions, and today we carry DNA from these encounters.

然而,他们消失前,至少数次曾与我们的祖先混种繁衍,今天我们携带的DNA就是来自他们的邂逅。

The first clues to ancient interbreeding surfaced in 2010, when scientists discovered that some modern humans — mostly Europeans — carry DNA that matches material recovered from Neanderthal fossils.

首次古人混种的线索出现在2010年,科学家发现一些人类——主要是欧洲人——携带的DNA与尼安德特人化石中提取的物质匹配。

Later studies showed that the forebears of modern humans first encountered Neanderthals after expanding out of Africa more than 50,000 years ago.

后来的研究表明,现代人的祖先首次与尼安德特人相遇是在5万多年前走出非洲之后。

But the Neanderthals were not the only extinct humans that our own ancestors found. A finger bone discovered in a Siberian cave, called Denisova, yielded DNA from yet another group of humans.

但是,尼安德特人不是仅有的我们祖先遇到的人类。在西伯利亚一个叫做丹尼索瓦的洞穴里发现的一个指骨中提取的DNA则来自另一个人类种群。

Research later indicated that all three groups — modern humans, Neanderthals and Denisovans — shared a common ancestor who lived roughly 600,000 years ago. And, perhaps no surprise, some ancestors of modern humans also interbred with Denisovans.

最新研究显示共有三种种群——现代人,尼安德特人和丹尼索瓦人——享有共同祖先,生活在大约60万年前。没什么奇怪的,一些现代人的祖先还混交了丹尼索瓦人。

Some of their DNA has survived in people in Melanesia, a region of the Pacific that includes New Guinea and the islands around it.

他们的一些DNA已经存在于生活在美拉尼西亚的人身上,那是一个太平洋区域,包括新几内亚和周边的岛屿。

Those initial discoveries left major questions unanswered, such as how often our ancestors interbred with Neanderthals and Denisovans. Scientists have developed new ways to study the DNA of living people to tackle these mysteries.

那些首次发现仍留下许多重要问题尚未解答,比如我们的祖先怎样经常和那两个种群的人混种繁衍。科学家们已经找到一个新方式去研究鲜活的人的DNA,去解决这些迷题。

Joshua M. Akey, a geneticist at the University of Washington, and his colleagues analyzed a database of 1,488 genomes from people around the world. The scientists added 35 genomes from people in New Britain and other Melanesian islands in an effort to learn more about Denisovans in particular.

约书亚·M·阿奇是华盛顿大学的遗传学家,和同事们分析了来自世界各地人种的1488个基因组数据库,科学家们又增加了35个来自新不列颠和美拉尼西亚岛屿的人基因组,努力了解更多,尤其是丹尼索瓦人。

The researchers found that all the non-Africans in their study had Neanderthal DNA, while the Africans had very little or none. That finding supported previous studies.

研究者发现,在他们的研究中所有非非洲人都具有尼安德特人DNA,而非洲人却非常少或者没有。这个发现支持了之前的研究成果。

But when Dr. Akey and his colleagues compared DNA from modern Europeans, East Asians and Melanesians, they found that each population carried its own distinctive mix of Neanderthal genes.

但是阿奇博士和同事比较来自现代欧洲人、东亚人和美拉尼西亚人的DNA发现每一种群携带与众不同的混合的尼安德特人的基因。

The best explanation for these patterns, the scientists concluded, was that the ancestors of modern humans acquired Neanderthal DNA on three occasions.

科学家推测,对于那些样品的最好解释是现代人类祖先经过三次机会获得了尼安德特人的DNA。

The first encounter happened when the common ancestor of all non-Africans interbred with Neanderthals.

第一次相遇发生在当所有非非洲人的共同祖先与尼安徳特人发生繁衍行为后。

The second occurred among the ancestors of East Asians and Europeans, after the ancestors of Melanesians split off. Later, the ancestors of East Asians — but not Europeans — interbred a third time with Neanderthals.

第二次产生于东亚人和欧洲人的祖先当中,在美拉尼西亚人的祖先分离后。后来,东亚人的祖先——不是欧洲人——第三次混交尼安德特人。

Earlier studies had hinted at the possibility that the forebears of modern humans had multiple encounters with Neanderthals, but until now hard data was lacking.

更早一些研究已经表明可能现代人的祖先有多次遭遇了尼安德特人,但直到现在还是缺乏有力数据证明。

“A lot of people have been arguing for that, but now they’re really providing the evidence for it,” said Rasmus Nielsen, a geneticist at the University of California, Berkeley, who was not involved in the new study.

“许多人一直支持那个观点,但直至现在才提供真正的证据证明它,”伯克利的加利福尼亚大学基因专家拉斯穆斯·尼尔森说。

The Melanesians took a different course. After a single interbreeding with Neanderthals, Dr. Akey found, their ancestors went on to interbreed just once with Denisovans, as well.

美拉尼西亚人带来了一个不同的进程。阿奇博士发现,同尼安德特人的单一混种后,同样,他们的祖先也仅一次与丹尼索瓦人进行混种。

Where that encounter could have taken place remains an enigma. The only place Denisovan remains have been found is Siberia, a long way from New Guinea.

发生遭遇的地方遗留下一个迷。这个丹尼德特人遗留的仅有的地方在西伯利亚已经被发现,距离新几内亚很长一段路。

It is possible that Denisovans ranged down to Southeast Asia, Dr. Akey said, crossing paths with modern humans who would later settle in Melanesia.

阿奇博士说,有可能尼安德特人扩展到东南亚,同后来住在美拉尼西亚的现代人相遇。

Dr. Akey and his colleagues also identified some regions of Neanderthal and Denisovan DNA that became more common in modern humans as the generations passed, suggesting that they provided some kind of a survival advantage.

阿奇博士和同事还鉴定了两个种群DNA的一些区域,那成为现代人许多共有的基因世代相传,推测他们提供了一些生存优势。

Many of the regions contain immune system genes, Dr. Akey noted.

阿奇博士注意到,这个区域保留着许多免疫系统基因。

“As modern humans are spreading out across the world, they’re encountering pathogens they haven’t experienced before,” he said. Neanderthals and Denisovans may have had genes that were adapted to fight those enemies.

“当现代人扩散到全世界时,遭遇到了之前未遇到过的致病菌,”他说。尼安徳特人和丹尼索瓦人可能已经有了对抗病菌基因。

“Maybe they really helped us survive and thrive in these new environments,” he said.

“可能他们真的帮助我的在新环境里幸存和繁衍下来,”他说。

Dr. Akey and his colleagues found that Neanderthal and Denisovan DNA was glaringly absent from four regions of the modern human genome.

阿奇博士和同事发现,两个种群的DNA明显缺失了现代人基因组的四个区域。

That absence may signal that these stretches of the genome are instrumental in making modern humans unique. Intriguingly, one of those regions includes a gene called FOXP2, which is involved in speech.

那些缺失可能表明基因组的那些延伸有助于现代人类的独特性。有趣的是,那些区域之一包括一个叫FOXP2的基因,这在演讲中没提到。

Scientists suspect that Neanderthals and Denisovans were not the only extinct races our ancestors interbred with.

科学家怀疑尼安德特人和丹尼索瓦人不是仅有的我们祖先与之混交而后灭绝的人种。

PingHsun Hsieh, a biologist at the University of Arizona, and his colleagues reported last month that the genomes of African pygmies contain pieces of DNA that came from an unknown source within the last 30,000 years.

亚利桑那大学的生物学家谢秉顺和同事上个月报告说,非洲侏儒族的基因组包含一段DNA,来自过去3万年,来源未知。

Dr. Akey and his colleagues are now following up with an analysis of African populations. “This potentially allows us to find new twigs on the human family tree,” he said.

阿奇博士和同事继续从事非洲人口分析报告。“这能让我们找到人类基因树的新枝,”他说。

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