Wednesday 28 September 2005
Modern humans reached Southeast Asia and Oceania in one of the first dispersals out of Africa. The resulting temporal overlap of modern and archaic humans-and the apparent morphological continuity between them-has led to claims of gene flow between Homo sapiens and H. erectus. (#11170891#)
Much more recently, an agricultural technology from mainland Asia spread into the region, possibly in association with Austronesian languages. (#11170891#)
Using detailed genealogical study of Y chromosome variation, the majority of current Austronesian speakers trace their paternal heritage to Pleistocene settlers in the region, as opposed to more-recent agricultural immigrants. (#11170891#)
A fraction of the paternal heritage, however, appears to be associated with more-recent immigrants from northern populations. (#11170891#)
The northern Neolithic component is very unevenly dispersed through the region, with a higher contribution in Southeast Asia and a nearly complete absence in Melanesia. (#11170891#)
Contrary to claims of gene flow (under regional continuity) between H. erectus and H. sapiens, no ancestral Y chromosome lineages have been found in a set of 1,209 samples. The finding excludes the possibility that early hominids contributed significantly to the paternal heritage of the region. (#11170891#)
The Y-chromosome data thus indicate independent histories for Australians and Melanesians, a finding that is in agreement with evidence from mtDNA but that contradicts some analyses of autosomal loci, which show a close relationship between Australian and Melanesian (specifically, highland Papua New Guinean) populations.
Since the Australian and New Guinean landmasses were connected when first colonized by humans > or =50,000 years ago but separated some 8,000 years ago, a possible way to reconcile all the genetic data is to infer that the Y-chromosome and mtDNA results reflect the past 8,000 years of independent history for Australia and New Guinea, whereas the autosomal loci reflect the long preceding period of common origin and shared history.
Two Y-chromosome haplotypes (M119C/M9G and M122C/M9G) that originated in eastern/southeastern Asia are present in coastal and island Melanesia but are rare or absent in both Australia and highland Papua New Guinea. This distribution, along with demographic analyses indicating that population expansions for both haplotypes began approximately 4,000-6,000 years ago, suggests that these haplotypes were brought to Melanesia by the Austronesian expansion.
Capelli C, Wilson JF, Richards M, Stumpf MP, Gratrix F, Oppenheimer S, Underhill P, Pascali VL, Ko TM, Goldstein DB. A predominantly indigenous paternal heritage for the Austronesian-speaking peoples of insular Southeast Asia and Oceania. Am J Hum Genet. 2001 Feb;68(2):432-43. PMID: #11170891#
Kayser M, Brauer S, Weiss G, Schiefenhovel W, Underhill PA, Stoneking M. Independent histories of human Y chromosomes from Melanesia and Australia. Am J Hum Genet. 2001 Jan;68(1):173-190. PMID: #11115381#
Melton T, Clifford S, Martinson J, Batzer M, Stoneking M. Genetic evidence for the proto-Austronesian homeland in Asia: mtDNA and nuclear DNA variation in Taiwanese aboriginal tribes. Am J Hum Genet. 1998 Dec;63(6):1807-23. PMID: #9837834#