Saturday, August 9, 2008
From Science Daily: Complete Neanderthal Mithocondrial Genome Sequenced from 38,000 Year Old Bone. Based on R. Green et al, 2008 (abstract only, full article behind a paywall).
As expected, the sequence falls at good distance of H. sapiens mtDNA range, discarding any matrilineal ancestry by that side. They estimate the age of the last common grandmother of our two species being some 660,000 years old (+/- 140,000 years), somewhat approaching the archeological record in this aspect but still falling short by some 240,000 years maybe.
This may be a reference for fine tunning of the molecular clock hypothesis, that (in my opinion) gives too young ages almost all the time, suggesting (in this case) a correction factor of roughly +28% (this is quite coincident with the correction required by Bonobo-Chimp divergence, by the way).
An interesting finding is that one specific protein encoded by mitochondrial DNA (subunit 2 of cytochrome c oxidase of the mitochondrial electron transport chain or COX2) has experienced a huge number of mutations in humans since the divergence. It is not clear what this means yet but it is clearly part of the small but meaningful genetic fraction that defines us for what we are as species.
Overall Neanders had evolved less than us from our common ancestors (guess they use Chimp genome for that comparison) what seems to imply that they had smaller population sizes, narrowing their genetic pool and limiting the effect of selection in it (what in the long run may have become a serious handicap for them). Nevertheless it is not fully clear if this narrowing of genetic diversity was an original Neanderthal feature or something caused by a bottleneck in their late history (notice that 38,000 years ago, they had already been displaced from most of their original range by our ancestors).
The researchers announce too that they are working in full sequencing of the Neanderthal genome. When this is achieved we will be better able to determine if there is any Neanderthal admixture in H. sapiens or not.