多国科学家合作研究发现，新的遗传学证据显示最早的美洲人分两批移民到达美洲。
参与该研究的有意大利、美国、西班牙和中国的科研工作者，中方参与研究的是来自云南大学和中科院昆明动物研究所的孔庆鹏博士。孔庆鹏于1999年9月自兰州大学考入中科院昆明动物研究所所攻读硕士学位， 2001年转为博士生，师从张亚平院士。其博士学位论文《东亚人群线粒体DNA系统发育基因组学研究》被评为2007年全国优秀博士学位论文。
在大约1.5万年到1.7万年前的末次盛冰期结束之后，一组移民从白令地区进入了北美，沿着没有结冰的太平洋沿岸前进，而另一组移民横跨了两个冰原之间的开放的陆地走廊，直接到达了落基山东部地区。（白令地区是在上一个冰期连接着东北西伯利亚和阿拉斯加的陆地。）这组科学家说，这些最早的美洲人后来形成了北美洲、中美洲和南美洲的几乎所有的现代美洲原住民群体，除了北美洲北部的纳得内以及爱斯基摩-阿留申群体这些重要的例外。
“近来基于考古学证据和环境记录的数据提示人类最早在1.5万年前从白令地区进入了美洲，而这种分散发生在解冻的太平洋沿海一带，”意大利帕维亚大学的Antonio Torroni说。“我们的研究如今揭示出了另一个新的可能性：在1.5万年前到1.7万年前来自白令地区的两个几乎相伴的移民路径导致了古印第安人——最早的美洲人——的散布。”
他说，古印第安人这样的双重起源对于涉及美洲原住民研究的所有学科都有重大意义。例如，这意味着并没有令人信服的理由去假定首批移民携带着单一的语系。
Torroni解释说，当哥伦布于1492年到达美洲的时候，美洲原住民生活的区域从白令海峡一直延伸到火地岛。这些原住群体的语言和文化多样性极大，这已经进一步刺激了专家就他们的相互关系和起源问题进行的广泛辩论。
近来，分子遗传学再加上考古学和语言学已经开始提供一些见解。在这项新的研究中，Torroni研究组的Ugo Perego 和Alessandro Achilli分析了来自两个罕见的单倍群的线粒体DNA，这意味着这些线粒体DNA有共同的母系祖先。线粒体是拥有自己的DNA的细胞器，它们可以让科学家追踪祖先和移民，因为它们是由母亲直接传给子女的。
他们的结果显示，被称为D4h3的单倍群从白令地区开始沿着太平洋沿海路径在美洲传播，迅速到达了火地岛。另有一个被称为X2a的单倍群在大约相同的时间里通过劳伦泰冰原和科迪勒拉冰原之间无冰的走廊传播，并仅限于在北美洲。
“最早的美洲人的双重起源从遗传学角度看来是一个引人注目的新发现，它让一个假说变得看上去有道理，即在一个很短的时期里，在动态变化的白令地区可能存在进入美洲的多个入口，”这组科学家得出结论说。（生物谷Bioon.com）
生物谷推荐原始出处：
Current Biology, Volume 19, Issue 1, 1-8, 13 January 2009 doi:10.1016/j.cub.2008.11.058
Distinctive Paleo-Indian Migration Routes from Beringia Marked by Two Rare mtDNA Haplogroups
Ugo A. Perego1,2,9,Alessandro Achilli1,3,9,Norman Angerhofer2,Matteo Accetturo1,Maria Pala1,Anna Olivieri1,Baharak Hooshiar Kashani1,Kathleen H. Ritchie2,Rosaria Scozzari4,Qing-Peng Kong5,6,Natalie M. Myres2,Antonio Salas7,Ornella Semino1,Hans-Jürgen Bandelt8,Scott R. Woodward2andAntonio Torroni1,,
1 Dipartimento di Genetica e Microbiologia, Università di Pavia, 27100 Pavia, Italy
2 Sorenson Molecular Genealogy Foundation, Salt Lake City, UT 84115, USA
3 Dipartimento di Biologia Cellulare e Ambientale, Università di Perugia, 27100 Perugia, Italy
4 Dipartimento di Genetica e Biologia Molecolare, Università La Sapienza, 00185 Rome, Italy
5 State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, 650223 Kunming, Yunnan, China
6 Laboratory for Conservation and Utilization of Bio-resource, Yunnan University, 650223 Kunming, Yunnan, China
7 Unidade de Xenética, Instituto de Medicina Legal, Facultad de Medicina, Universidad de Santiago de Compostela, 15782 Santiago de Compostela, Galicia, Spain
8 Department of Mathematics, University of Hamburg, 20146 Hamburg, Germany
9 These authors contributed equally to this work
It is widely accepted that the ancestors of Native Americans arrived in the New World via Beringia approximately 10 to 30 thousand years ago (kya). However, the arrival time(s), number of expansion events, and migration routes into the Western Hemisphere remain controversial because linguistic, archaeological, and genetic evidence have not yet provided coherent answers. Notably, most of the genetic evidence has been acquired from the analysis of the common pan-American mitochondrial DNA (mtDNA) haplogroups. In this study, we have instead identified and analyzed mtDNAs belonging to two rare Native American haplogroups named D4h3 and X2a.Phylogeographic analyses at the highest level of molecular resolution (69 entire mitochondrial genomes) reveal that two almost concomitant paths of migration from Beringia led to the Paleo-Indian dispersal approximately 1517 kya. Haplogroup D4h3 spread into the Americas along the Pacific coast, whereas X2a entered through the ice-free corridor between the Laurentide and Cordilleran ice sheets. The examination of an additional 276 entire mtDNA sequences provides similar entry times for all common Native American haplogroups, thus indicating at least a dual origin for Paleo-Indians.A dual origin for the first Americans is a striking novelty from the genetic point of view, and it makes plausible a scenario positing that within a rather short period of time, there may have been several entries into the Americas from a dynamically changing Beringian source. Moreover, this implies that most probably more than one language family was carried along with the Paleo-Indians.
