多國科學家合作研究發(fā)現(xiàn)，新的遺傳學證據(jù)顯示最早的美洲人分兩批移民到達美洲,。
參與該研究的有意大利,、美國、西班牙和中國的科研工作者,，中方參與研究的是來自云南大學和中科院昆明動物研究所的孔慶鵬博士,。孔慶鵬于1999年9月自蘭州大學考入中科院昆明動物研究所所攻讀碩士學位,， 2001年轉(zhuǎn)為博士生,，師從張亞平院士。其博士學位論文《東亞人群線粒體DNA系統(tǒng)發(fā)育基因組學研究》被評為2007年全國優(yōu)秀博士學位論文,。
在大約1.5萬年到1.7萬年前的末次盛冰期結(jié)束之后,，一組移民從白令地區(qū)進入了北美，沿著沒有結(jié)冰的太平洋沿岸前進,，而另一組移民橫跨了兩個冰原之間的開放的陸地走廊,，直接到達了落基山東部地區(qū)。（白令地區(qū)是在上一個冰期連接著東北西伯利亞和阿拉斯加的陸地,。）這組科學家說，這些最早的美洲人后來形成了北美洲,、中美洲和南美洲的幾乎所有的現(xiàn)代美洲原住民群體,，除了北美洲北部的納得內(nèi)以及愛斯基摩-阿留申群體這些重要的例外,。
“近來基于考古學證據(jù)和環(huán)境記錄的數(shù)據(jù)提示人類最早在1.5萬年前從白令地區(qū)進入了美洲，而這種分散發(fā)生在解凍的太平洋沿海一帶,，”意大利帕維亞大學的Antonio Torroni說,。“我們的研究如今揭示出了另一個新的可能性：在1.5萬年前到1.7萬年前來自白令地區(qū)的兩個幾乎相伴的移民路徑導(dǎo)致了古印第安人——最早的美洲人——的散布。”
他說,，古印第安人這樣的雙重起源對于涉及美洲原住民研究的所有學科都有重大意義,。例如，這意味著并沒有令人信服的理由去假定首批移民攜帶著單一的語系,。
Torroni解釋說,，當哥倫布于1492年到達美洲的時候，美洲原住民生活的區(qū)域從白令海峽一直延伸到火地島,。這些原住群體的語言和文化多樣性極大,，這已經(jīng)進一步刺激了專家就他們的相互關(guān)系和起源問題進行的廣泛辯論。
近來,，分子遺傳學再加上考古學和語言學已經(jīng)開始提供一些見解,。在這項新的研究中，Torroni研究組的Ugo Perego 和Alessandro Achilli分析了來自兩個罕見的單倍群的線粒體DNA,，這意味著這些線粒體DNA有共同的母系祖先,。線粒體是擁有自己的DNA的細胞器，它們可以讓科學家追蹤祖先和移民,，因為它們是由母親直接傳給子女的,。
他們的結(jié)果顯示，被稱為D4h3的單倍群從白令地區(qū)開始沿著太平洋沿海路徑在美洲傳播,，迅速到達了火地島,。另有一個被稱為X2a的單倍群在大約相同的時間里通過勞倫泰冰原和科迪勒拉冰原之間無冰的走廊傳播，并僅限于在北美洲,。
“最早的美洲人的雙重起源從遺傳學角度看來是一個引人注目的新發(fā)現(xiàn),，它讓一個假說變得看上去有道理，即在一個很短的時期里,，在動態(tài)變化的白令地區(qū)可能存在進入美洲的多個入口,，”這組科學家得出結(jié)論說。（生物谷Bioon.com）
生物谷推薦原始出處：
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.
