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First Americans arrived as 2 separate migrations, according to new genetic evidence
The first people to arrive in America traveled as at least two separate groups to arrive in their new home at about the same time, according to new genetic evidence published online on January 8th in Current Biology, a Cell Press publication.

After the Last Glacial Maximum some 15,000 to 17,000 years ago, one group entered North America from Beringia following the ice-free Pacific coastline, while another traversed an open land corridor between two ice sheets to arrive directly into the region east of the Rocky Mountains. (Beringia is the landmass that connected northeast Siberia to Alaska during the last ice age.) Those first Americans later gave rise to almost all modern Native American groups of North, Central, and South America, with the important exceptions of the Na-Dene and the Eskimos-Aleuts of northern North America, the researchers said.

" Recent data based on archeological evidence and environmental records suggest that humans entered the Americas from Beringia as early as 15,000 years ago, and the dispersal occurred along the deglaciated Pacific coastline," said Antonio Torroni of Università di Pavia, Italy. "Our study now reveals a novel alternative scenario: Two almost concomitant paths of migration, both from Beringia about 15,000 to 17,000 years ago, led to the dispersal of Paleo-Indians—the first Americans."

Such a dual origin for Paleo-Indians has major implications for all disciplines involved in Native American studies, he said. For instance, it implies that there is no compelling reason to presume that a single language family was carried along with the first migrants.

When Columbus reached the Americas in 1492, Native American occupation stretched from the Bering Strait to Tierra del Fuego, Torroni explained. Those native populations encompassed extraordinary linguistic and cultural diversity, which has fueled extensive debate among experts over their interrelationships and origins.

Recently, molecular genetics, together with archaeology and linguistics, has begun to provide some insights. In the new study, Ugo Perego and Alessandro Achilli of Torroni's team analyzed mitochondrial DNA from two rare haplogroups, meaning mitochondrial types that share a common maternal ancestor. Mitochondria are cellular components with their own DNA that allow scientists to trace ancestry and migration because they are passed on directly from mother to child over generations.

Their results show that the haplogroup called D4h3 spread from Beringia into the Americas along the Pacific coastal route, rapidly reaching Tierra del Fuego. The other haplogroup, X2a, spread at about the same time through the ice-free corridor between the Laurentide and Cordilleran Ice Sheets and remained restricted to North America.

" A dual origin for the first Americans is a striking novelty from the genetic point of view and 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," the researchers concluded.

根据1月8日发表在细胞出版社出版的《当代生物学》(Current Biology)网站上的新的遗传学证据,首批到达美洲的人们至少以两个不同的群体几乎同一时间到达了他们的新的家乡。


“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。”



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。







作者:admin@医学,生命科学    2011-11-05 20:36