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

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

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问题     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? 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.
    Now they may have found an answer.
    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.
    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
    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.
    Early studies of bits of DNA also supported this scenario. 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.
    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.
    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.
    He concluded that the ancestors of Aboriginals split 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.
    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 Lambert, a geneticist at Griffith University in Australia, who was already meeting with aboriginal communities about beginning such a study.
    Their new paper also includes DNA from people in Papua New Guinea All told, the scientists were able to sequence 83 genomes from aboriginal Australians and 25 from people in Papua New Guinea.
    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.
    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.
    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.
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答案 现代入大约是在20万年前从非洲某地进化而来，但人类是如何在地球其他角落繁衍生息的呢?人类是一次性从非洲大规模迁出，抑或是在几万年间一波接一波地离开那片大陆的?这是关于人类进化最大的问题之一，几十年来一直困扰着科学家们。 现在他们可能找到了答案。 周三，《自然》(Nature)期刊发表了一系列史无前例的基因分析报告，3个独立的研究团队都得出结论，非洲之外的所有人类祖先都可以溯源到5到8万年前从非洲迁出的同一个族群。 每个研究团队都利用若干基因组来探究有关人类起源的不同问题，比如，人类如何扩散到非洲各地?另一些人又是如何在澳洲繁衍生存?所有的研究都是为了弄明白人类是如何走出非洲的这个问题。 20世纪80年代，一群古人类学家和遗传学家开始支持一种假说，即现代入大约在5万年前从非洲一次性迁出。在考古遗址发现的骸骨和工具清楚地表明了现代入在欧洲、亚洲和澳洲的存在。早期对脱氧核糖核酸(DNA)片段的研究也支持这一说法。然而，也有迹象表明，至少在5万年前，一些现代入就已经生活在非洲之外的土地，这可能是更早期迁徙潮的一部分。 2011年，哥本哈根大学(University of Copenhagen)的著名遗传学家埃斯克.维勒斯列夫 (Eske Wmerslev)和同事们报道了关于现代入起源于这批早期迁徙潮的证据。澳大利亚的博物馆里保存了一位当地土著的一绺头发，已有百年历史，维勒斯列夫和他的同事们利用它来重建了这位土著的基因组，这是首例古人类基因组测序工作。分析得出，该土著居民的DNA中包含了许多不存在于欧亚人种基因中的特殊变异。他得出的结论是，澳大利亚土著居民的祖先来自另一支非洲以外的人种，他们向东迁徙，并最终在6.2到7.5万年前到达东亚。数万年后，另一个非洲独立种群才到达欧亚大陆。 但仅凭一份单薄的基因组研究得出这个结论是不够可靠的，因此，维勒斯列夫决定与澳大利亚土著居民取得联系，看看他们是否愿意参与到新的基因研究中。他与澳大利亚格里菲斯大学 (Griffith University)的遗传学家大卫.兰伯特(David Lambert)合作。当时。兰伯特已经开始与澳大利亚土著居民见面，并与他们讨论开始类似的研究。他们最新发表的文章还包括了巴布亚新几内亚(Papua New Guinea)人的DNA。科学家们总共对83个澳大利亚土著居民以及25个巴布亚新几内亚人的基因组进行测序。 与此同时，来自爱沙尼亚生物中心(Estonian Biocentre)的马特.梅特斯帕鲁(Mait Metspalu)带领着一个拥有98名科学家的团队正在攻克另一个基因组收集项目。他们从148个种群中挑选样本，这些基因组大部分来自欧洲和亚洲，小部分来自非洲和澳洲。并对这483个基因组进行了高精度测序。 来自哈佛医学院(Harvard Medical School)的遗传学家大卫.赖克(David Reich)与同事们建立了第3个基因组数据库，收集了来自五大洲的数据。西蒙斯基因组多样性项目(Simons Genome Diversity Project)由西蒙斯基金会(Simons Foundation)和美国国家科学基金会(National Science Foundation)赞助，包含了来自142个种群的300个高质量基因组。 赖克和他的同事研究这些数据，以期从中找到人类种群在基因上彼此分离开来最古老的证据。他们发现，现今居住在南非、以狩猎采集为生的克瓦桑语族人(KhoiSan)的祖先，在大约20万年前就开始与当时其他人类分离开采，并于10万年前与其他种群完全隔离。
解析     1.第6段第一句scenario为多义词，有“剧本”“情节”“方案”等义项。根据本文语境，this scenario指代的是上一段提到的a hypothesis，即“现代入大约在6万年前从非洲一次性迁出”的假说，故此处scenanl0译为“说法”更为合适。
    2.第8段第一句the first reconstruction of its kind，若直译为“这是第一次进行这样的重建”则会显得生硬，可将形容词first转译作名词“首例”。
    3.第10段第一句big为多义词，有“大的”“重要的”等义项。下文提到这是从一份单薄的(single fragile)基因组研究得出的结论，由此可知，仅凭从头发提取到的基因组，研究者就得出澳大利亚土著居民起源于更早期迁徙潮的结论，这可能是站不住脚的，这里big带有贬义色彩，指“空泛的”意思，译为“不够可靠的”更为合适。
    4.第14段第二句hunter-gatherers“狩猎采集者”为the KhoiSan的同位语，在翻译时可将其词性进行转换，将名词译为介词词组“以狩猎采集为生”，使译文更加连贯顺畅。
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