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研究基因传递能揭示不同种族之间的迁移方式

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New genetic evidence suggests aboriginal Australians may be directly descended from the earliest of several human groups that left Africa and colonized the world, a challenge to a widely held model that argues for a single dispersal from Africa.


最新遗传学证据表明，澳大利亚土著居民可能直接源于最早的几批离开非洲并在世界各地居住的人群之一，而之前人们普遍认为迁出非洲的只有一批人。



In a notabletechnical feat, published in the journal Science, researchers assembled a genome using a lock of hair donated by a young aboriginal man from Australia 100 years ago. That DNA was compared with the full genomes of two Western Africans, three Han Chinese and two Europeans, and more broadly with other partial genomes. Genetic markers get passed down from one generation to the next, and studying gene flow can reveal migration patterns among different ethnic groups.


《科学》杂志（Science）发表论文称，在一项引人注目的技术壮举中，研究人员用100年前一名澳大利亚年轻土著居民捐献的一缕头发组成了一个基因组，将这个DNA与两名西非人、三名中国汉族人和两名欧洲人的全基因组进行对比，并与其他的部分基因组进行对比。遗传标记能够代代相传，研究基因传递能揭示不同种族之间的迁移方式。



The study suggests a first wave of Africans traveled to Australia between 62,000 and 75,000 years ago and gave rise to the Aborigines, while a second dispersal -- one that ultimately went northward and another eastward -- some 25,000 to 38,000 years ago led to modern Europeans and Asians. Based on these findings, aboriginal Australians would represent one of the oldest continuous populations outside Africa.


这项研究显示，第一批非洲人迁移到澳大利亚是在6.2万到7.5万年前，由此产生了澳大利亚土著人，而第二批是在约2.5万到3.8万年前，产生了现代欧洲人和亚洲人。最终的迁移方向是一个向北一个向东。根据这些研究结果，澳大利亚土著人可能是非洲以外最古老的连续进化的人种之一。



Another conclusion: These early human explorers were surprisingly intrepid and capable as they moved from Africa, likely along the southern coast of what is now southeast Asia and, ultimately, to Australia.


还有一个结论是：这些早期的人类探索者迁出非洲时具备惊人的勇气和能力，他们可能是沿着现在东南亚的南部海岸出发，最终到达澳大利亚。



'They would have had to use boats even though the sea level was lower back then, and they wouldn't have been able see the land mass of Australia' from the southeast Asian shore some 50 miles away, said Eske Willerslev, an evolutionary biologist at the University of Copenhagen and senior author of the paper. 'We used to think they were just wandering around -- we have underestimated them.'


哥本哈根大学（University of Copenhagen）进化生物学家、上述论文首席作者威勒斯雷夫（Eske Willerslev）说，虽然当时的海平面较低，但他们应该得用船，他们也不可能从距离东南亚海岸约50英里（80公里）的地方看到澳大利亚的大片陆地；以前我们以为他们只是在到处漫游，现在看来是低估了他们。



The latest finding is unlikely to be the last word on how humans came to colonize the planet. Other DNA evidence supports the discipline's conventional view that there was only a single dispersal from Africa, some 60,000 to 70,000 years ago. According to that model, the explorers traveled to Arabia where one branch split off and headed north -- becoming Europeans -- while a second group populated India and Australia. The rest of Eurasia, including modern-day China, was then populated by southeast Asians moving northward.


上述最新发现不可能为人类如何分布于整个地球盖棺定论。其他的DNA证据都支持非洲仅有一批迁移者的传统观点，迁徙时间约为6万到7万年前。根据这种模式，早期探索者迁移到阿拉伯半岛，其中一群人分道扬镳往北走成为欧洲人，另一群人落户在了印度和澳大利亚。在欧亚大陆的剩余部分，包括现在的中国在内，那个时候居住的是向北迁移的东南亚人。



Martin Richards, professor of archeogenetics at the University of Leeds, England, who read the Science study but wasn't involved in the research, is skeptical. 'The argument for multiple dispersals put forward here comes entirely from a single newly developed statistical test based on just four complete genomes,' he said. 'None of the other analyses support it, and many argue against it.'


英格兰利兹大学（University of Leeds）考古遗传学教授理查兹（Martin Richards）对《科学》杂志中的这项研究表示怀疑，他读了这篇论文但并未参与研究。他说，这篇文章提出的多批迁移论完全是来自一个新开发的统计测试，仅仅是基于四组完整基因组；现有的其他分析学说都不支持这个观点，而且很多还与之相反。



The power and rapidly falling cost of gene-sequencing technology is transforming the way scientists delve into the story of how humans evolved and spread. In 2009, scientists announced the first draft of the genome of Neanderthals; it was later found that humans and Neanderthals likely interbred, with today's humans owing some of their disease-fighting genes to those ancient trysts.


基因测序技术的力量及迅速降低的成本正在改变科学家研究人类进化和迁移过程的方式。2009年，科学家宣布初步完成了尼安德特人（Neanderthals）的基因测序；后来发现人类和尼安德特人可能是杂交繁殖，现在人类的某些抗病基因源于这些远古的交配。



Scientists hope to use similar genetic data to reconstruct the history of peoples and cultures in more recent times.


科学家希望用相似的遗传学数据来重建近代种族和文化的历史。



The challenges are many -- and they aren't just scientific. Dr. Willerslev and his colleagues needed DNA from an Australian Aborigine who wouldn't have carried genes from European settlers.


存在很多挑战，并且不仅仅是科学上的挑战。威勒斯雷夫和他的同事们需要一位未携带欧洲移民基因的澳大利亚土著人的DNA。



Dr. Willerslev found the DNA he needed in a 100-year-old hair sample from an Aborigine who lived in a relativelyremote area of southwest Australia. After locating the sample in a collection maintained at Cambridge University, England, he traveled to southwest Australia and obtained permission from local aboriginal tribes to use the sample.


威勒斯雷夫从一位100年前居住在澳大利亚西南部偏远地区的土著人的头发样本中找到了他需要的DNA。在英格兰剑桥大学（Cambridge University）保存的藏品中找到这个样本后，他前往澳大利亚西南地区，从当地土著部落那里获得了该样本的使用许可。



The human genome contains three billion DNA base pairs. But the DNA of the century-old aboriginal hair sample had degraded into millions of fragments, each an average of 69 base pairs in length. The scientists were able to reconstruct only 60% of the total genome. By comparing this old genome with other people's genomes, Dr. Willerslev and his colleagues concluded that there had been separate human dispersals from Africa into Asia.


人类的基因组包含30亿个DNA硷基对。但这个百年头发样本的DNA已经分解成了数百万个片段，每个片段的长度平均为69个硷基对。科学家们只能重组其中60%的基因组。通过将其与其他种族的基因组进行对比，威勒斯雷夫和他的同事们得出结论，还有几批人从非洲迁移到了亚洲。



That may not be the final story. 'We need comparisons with a larger number of genome sequences' to conclude whether there was just one or several eastward dispersals' from Africa, said Dr. Richards.


这可能并不是最后的结论。理查兹说，我们需要与更大规模的基因组序列进行对比，以确认从非洲向东迁移的人类是只有一批还是多批。



Gautam Naik


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