Close correspondence between quantitative- and molecular-genetic divergence times for Neandertals and modern humans
- From: Jack Linthicum <jacklinthicum@xxxxxxxxxxxxx>
- Date: Tue, 18 Mar 2008 12:19:29 -0700 (PDT)
"The a" is as printed in the source.
Timothy Weaver, an anthropologist at the University of California at
Davis and colleagues Charles Roseman and Chris Stringer created a
model used prior information on how microsatellites, aka "junk DNA,"
can change, or drift, over time in The a species. Over time, those
changes can accumulate enough for an entirely new species to evolve.
The researchers applied the model to 37 cranial measurements collected
on 2,524 modern and 20 Neanderthal specimens. Their findings are
published in this week's Proceedings of the National Academy of
Sciences. Abstract below.
The Neanderthal-Human Split: (Very) Ancient History
Jennifer Viegas, Discovery News
March 17, 2008 -- Neanderthals and humans once shared a common
ancestor, but we split from the stocky, hairy hominid group as long as
400,000 to 350,000 years ago, concludes a new study.
That estimate matches prior DNA studies, putting a date to the time
when human beings first emerged on the planet. But would these first
humans have been anatomically just like us? Probably not, suggests
lead author Timothy Weaver, an anthropologist at the University of
California at Davis.
"Early fossils along this lineage are quite different from later
ones," he told Discovery News.
Fast evolution, in fact, probably drove the initial Neanderthal/human
divergence, which likely began as genetic drift -- random changes in
DNA. As the two groups parted ways, their changing environments likely
drove more substantial changes in body shape and size, in response to
differing needs.
Weaver and colleagues Charles Roseman and Chris Stringer created a
model to determine how long it would have taken genetic drift to
create the cranial differences observed between Neanderthal and modern
human skeletons.
The model used prior information on how microsatellites, aka "junk
DNA," can change, or drift, over time in The a species. Over time,
those changes can accumulate enough for an entirely new species to
evolve.
The researchers applied the model to 37 cranial measurements collected
on 2,524 modern and 20 Neanderthal specimens. Their findings are
published in this week's Proceedings of the National Academy of
Sciences.
Now that scientists have a better idea on when Neanderthals split from
humans, they can zone in on which species might have been our common
ancestor. They do this mostly by process of elimination. Fossils found
long before 400,000 years ago, such as the 800,000-year-old Atapuerca
humans from Spain, are simply too old to represent the common
ancestor.
"I support the concept of a widespread ancestral species, Homo
heidelbergensis," Stringer, a paleontologist at the Natural History
Museum of London, told Discovery News.
Neanderthal features began to emerge from Homo heidelbergensis just
before 500,000 years ago. "Heidelberg Man" was muscular and tall, had
a relatively large brain, and usually grew to heights of 6 feet or
more. Markings on bones suggest the burly hominid dined on enormous
animals, such as mammoths, rhinos and elephants, some of which weighed
over 1,500 pounds.
Stringer thinks that since Neanderthals and humans split relatively
early, "we may need to designate the earlier part [on the human side]
as 'Archaic sapiens.'" That would allow researchers to account for the
different types of human fossils that fall between the divergence date
and the appearance of more modern-looking people in Africa around
50,000 years ago.
Osbjorn Pearson, an associate professor of anthropology at the
University of New Mexico, recently conducted similar research on
Neanderthals and humans. He told Discovery News that he fully agrees
with the new findings.
"From their, and other scientists' previous research, it has become
clear that many of the physical differences between human skulls are
due to random genetic changes that make populations diverge over
time," Pearson said.
"It is gratifying -- and, for many anthropologists, perhaps unexpected
-- that the bones and genes tell the same story."
"The results also reinforce the conclusion that it is unlikely that
Neanderthals...contributed substantially to the modern human gene
pool."
http://dsc.discovery.com/news/2008/03/17/human-neanderthal-split-print.html
Published online on March 17, 2008
Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0709079105
ANTHROPOLOGY
Close correspondence between quantitative- and molecular-genetic
divergence times for Neandertals and modern humans
Timothy D. Weaver*, Charles C. Roseman§, and Chris B. Stringer¶
*Department of Anthropology, University of California, One Shields
Avenue, Davis, CA 95616; {dagger}Department of Human Evolution, Max
Planck Institute for Evolutionary Anthropology, Deutscher Platz 6,
D-04103 Leipzig, Germany; §Department of Anthropology, University of
Illinois at Urbana-Champaign, 109 Davenport Hall, 607 South Matthews
Avenue, Urbana, IL 61801; and ¶Department of Palaeontology, Natural
History Museum, London SW7 5BD, United Kingdom
Edited by Erik Trinkaus, Washington University, St. Louis, MO, and
approved January 17, 2008 (received for review September 27, 2007)
Abstract
Recent research has shown that genetic drift may have produced many
cranial differences between Neandertals and modern humans. If this is
the case, then it should be possible to estimate population genetic
parameters from Neandertal and modern human cranial measurements in a
manner analogous to how estimates are made from DNA sequences.
Building on previous work in evolutionary quantitative genetics and on
microsatellites, we present a divergence time estimator for neutrally
evolving morphological measurements. We then apply this estimator to
37 standard cranial measurements collected on 2,524 modern humans from
30 globally distributed populations and 20 Neandertal specimens. We
calculate that the lineages leading to Neandertals and modern humans
split {approx}311,000 (95% C.I.: 182,000 to 466,000) or 435,000 (95%
C.I.: 308,000 to 592,000) years ago, depending on assumptions about
changes in within-population variation. These dates are quite similar
to those recently derived from ancient Neandertal and extant human DNA
sequences. Close correspondence between cranial and DNA-sequence
results implies that both datasets largely, although not necessarily
exclusively, reflect neutral divergence, causing them to track
population history or phylogeny rather than the action of diversifying
natural selection. The cranial dataset covers only aspects of cranial
anatomy that can be readily quantified with standard osteometric
tools, so future research will be needed to determine whether these
results are representative. Nonetheless, for the measurements we
consider here, we find no conflict between molecules and morphology.
craniometrics | evolutionary quantitative genetics | microsatellites |
population genetics | human evolution
Footnotes
Author contributions: T.D.W., C.C.R., and C.B.S. designed research;
T.D.W. and C.C.R. performed research; C.B.S. contributed new reagents/
analytic tools; and T.D.W., C.C.R., and C.B.S. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
{ddagger}To whom correspondence should be addressed. E-mail:
tdweaver@xxxxxxxxxxx
(c) 2008 by The National Academy of Sciences of the USA
http://www.pnas.org/cgi/content/abstract/0709079105v1
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