June 14, 2008
What Are the Chances of Turning Neanderthal?
HUMAN DEVELOPMENT There is added evidence that chance, rather than natural selection, best explains why the skulls of modern humans and ancient Neanderthals evolved differently. The findings of anthropologist Tim Weaver of the University of California, Davis, may alter how scientists think about human evolution.
Weaver's study builds on findings from a report he and his colleagues published last year in which the team compared cranial measurements of modern human skulls and Neanderthal specimens. The researchers concluded that random genetic change, or genetic drift, most likely accounts 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 those 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, the other on examining 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 concludes. "This may have interesting implications for our understanding of human evolution."
Copyright Society for Advancement of Education Jun 2008
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