March 20, 2008 — New research led by UC Davis
anthropologist Tim Weaver 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.
Weaver’s study appears in the March 17 issue of the Proceedings of
the National Academy of Sciences. It 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
Weaver conducted the research with Charles Roseman, an
anthropologist at the University of Illinois at Urbana-Champaign, and
Chris Stringer, a paleontologist at the Natural History Museum in
Source : University of California, Davis