Tuesday, March 18, 2008

Neanderthals The Result of Genetic Drift

New research adds to the evidence that chance, rather than natural selection, best explains why the skulls of modern humans and ancient Neanderthals evolved differently. The findings may alter how anthropologists think about human evolution.

The study builds on findings from a study he and his colleagues published last year in the Journal of Human Evolution, in which the team compared cranial measurements of 2,524 modern human skulls and 20 Neanderthal specimens. The researchers concluded that random genetic change, or genetic drift, most likely account for the cranial differences.

In their new study, Weaver and his colleagues crunched their fossil data using sophisticated mathematical models -- and calculated that Neanderthals and modern humans split about 370,000 years ago. The estimate is very close to estimates derived by other researchers who have dated the split based on clues from ancient Neanderthal and modern-day human DNA sequences.

The close correlation of the two estimates -- one based on studying bones, one based on studying genes -- demonstrates that the fossil record and analyses of DNA sequences give a consistent picture of human evolution during this time period.

"A take-home message may be that we should reconsider the idea that all morphological (physical) changes are due to natural selection, and instead consider that some of them may be due to genetic drift," Weaver said. "This may have interesting implications for our understanding of human evolution." link

Close correspondence between quantitative-and molecular-genetic divergence times for Neandertals and modern humans. 2008. T. D. Weaver et al. PNAS, published on-line March 17, 2008.

Lobby cards from, "Creatures That Time Forgot".