Monday, May 07, 2007

Australian Aborignals, a people that dwelt alone?   posted by Razib @ 5/07/2007 02:40:00 PM

Ancient Australians Were a People Apart. Money shot:
A team headed by Georgi Hudjashov of Tartu University in Estonia analyzed variation in the Y chromosome and mitochondrial DNA (mtDNA, which is inherited only from women) in several hundred people from Australia and New Guinea. By knowing the mutation rate of mtDNA and comparing Australian samples with those from Asian populations, the team ascertained that the Australian and New Guinean populations branched off from a parent population 50,000 years ago, and that no significant additions to the aboriginal Australian gene pool had been made until modern times. "Australia was colonized, then nobody else came," says co-author Peter Underhill of Stanford University in Palo Alto, California.

The study will be published in PNAS this week. The article notes that there seems to have been morphological evolution in Australia over the past 50,000 years (e.g., from gracile to robust). Some have adduced from this that waves of migration of disparate peoples. But, remember, phylogeny does not necessarily track morphology over evolutionary time scales. In Dragon Bone Hill two paleoanthropologists make the argument that the robust physique of Australian Aboriginals was a response to selective pressures derived from intercommunal melees (!?!?! You read that right!). Whatever the truth, I don't doubt that 50,000 years is long enough a time period that in situ selection upon extant genetic variation could reshape the modal morphology of populations. Additionally, we know that Australia was an not island ark totally separate from the rest of humanity, dingos were introduced within the last 10,000 years. It seems almost certain that the northern coast of Australia was occasionally visited by sailors from the Indonesian archipelago (for supplies such as water). Let's take at face value the results derived from these two neutral lineages and assume it is an accurate representation of total genome content in regards to ancestry. Explicitly, the vast majority of lines of ancestry of Australian Aboriginals today coalesce back to a founding population which reached the continent's shores 50,000 years ago. That does not negate the possibility that alleles may have crossed from the Eurasian mainland and so driven adaptive evolution amongst Australian populations. Just as they picked up the dingo from traditions of canine domestication originating in Eurasia, so Aboriginals may exhibit a non-ancestral genetic signature on many loci which are phenotypically salient.