Asian DNA Enters Human Origins Fray

 A large genetic analysis of Chinese citizens and others indicates that modern humans, probably originating in Africa, migrated across Asia in a southeasterly direction before heading north into what is now China.

 This challenges the long-standing view of Chinese paleontologists, based on fossil evidence, that an East Asian branch of Homo erectus independently evolved into H. sapiens.

"It is now probably safe to conclude that modern humans originating in Africa constitute the majority of the current gene pool in East Asia," holds a research team headed by geneticist Li Jin of the University of Texas in Houston.

 The scientists, who come from several institutions participating in the Chinese Human Genome Diversity Project, examined genetic relationships among 28 of China's 56 official ethnic groups, including the majority Han population. Analysis focused on short DNA segments, called microsatellites, that over time accumulate varying numbers of repeated sequences of nucleotides, the basic DNA subunits.

 The researchers first used a computer program to construct an evolutionary tree of genetic relationships-based on 30 microsatellites per person-among 14 East Asian populations, 3 populations from Africa, and 8 from elsewhere in the world. This mathematical approach assumes that relatively isolated populations branch off from evolutionary precursors in a treelike progression.

 The researchers constructed a second such genetic tree, based on 15 of the microsatellites, for 32 East Asian populations (including the 28 Chinese groups) and the 11 non-Asian populations.

 Both reconstructions indicate that East Asian populations derived from a single lineage in Southeast Asia, Jin and his coworkers report in the Sept. 29 Proceedings of the National Academy of Sciences. This result is consistent with the existence of a prior genetic source in Africa, but not with a separate emergence of modern humans in East Asia, the scientists contend.

 The new DNA data also show that genetic differences exist between southern and northern Chinese groups and that greater genetic variation occurs in the southern populations.

 The East Asian findings fit with the theory that humans migrated out of East Africa around 100,000 years ago and, perhaps by crossing short stretches of sea, traveled along Asia's southern coast before heading into East Asia, says geneticist L. Luca Cavalli-Sforza of Stanford University School of Medicine in an accompanying commentary. Further studies need to include DNA from mid-Asian populations to test for other possible expansion routes, he says.

 However, Alan R. Templeton, a geneticist at Washington University in St. Louis, challenges the use of evolutionary trees. Jin's group did not employ methods for establishing whether far-flung populations maintained genetic ties through interbreeding, which would have undermined the assumption of a branching of separate ethnic groups, he says.

 In an upcoming American Anthropologist, Templeton reports that regional evolution in areas outside China, which he analyzed using others' data sets, occurred within a network of DNA links rather than a tree.