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http://www.sciencedaily.com/releases/2010/11/
101105124241.htm
New Statistical Model Moves Human Evolution Back Three Million Years
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A new statistical model suggests that evolutionary divergence of humans from
chimpanzees likely occurred some 8 million years ago, rather than the 5 million
year estimate widely accepted by scientists. (Credit: iStockphoto/Eric Gevaert)
ScienceDaily (Nov. 5, 2010) Evolutionary divergence of humans from
chimpanzees likely occurred some 8 million years ago rather than the 5 million
year estimate widely accepted by scientists, a new statistical model suggests.
The revised estimate of when the human species parted ways from its closest
primate relatives should enable scientists to better interpret the history of
human evolution, said Robert D. Martin, curator of biological anthropology at
the Field Museum, and a co-author of the new study appearing in the journal
Systematic Biology.
Working with mathematicians, anthropologists and molecular biologists, Martin
has long sought to integrate evolutionary information derived from genetic
material in various species with the fossil record to get a more complete
picture.
Comparing DNA among related animals can provide a clear picture of how their
shared genes evolved over time, giving rise to new and separate species, Martin
said. But such molecular information doesn't yield a timetable showing when the
genetic divergence occurred.
Fossil evidence is the only direct source of information about long-extinct
species and their evolution, Martin and his colleagues said, but large gaps in
the fossil record can make such information difficult to interpret. For a
generation, paleontologists have estimated human origins at 5 million to 6
million years ago.
But that estimate rests on a thin fossil record. By looking at all of today's
primate species, all of the known fossil primates and using DNA evidence,
computer models suggest a longer evolutionary timetable. The new analysis
described in the Systematic Biology paper takes into account gaps in the fossil
record and fills in those gaps statistically.
Such modeling techniques, which are widely used in science and commerce, take
into account more overall information than earlier processes used to estimate
evolutionary history using just a few individual fossil dates, Martin said. It
can give scientists a broader perspective for interpreting data.
One example is a skull fossil discovered in Chad (central Africa) earlier in
this decade. The fossil, named Sahelanthropus tchadensis and nicknamed Toumaï
(which means "hope of life" in the local Goran language), raised great interest
because it has many human characteristics. But consensus on how to classify the
discovery has been elusive particularly because the fossil is about 7 million
years old, well beyond the accepted time frame for human evolution.
Under the new estimate, Toumaï would fall within the period after the human
lineage split from chimpanzees, Martin said.
The new approach to dating evolutionary history builds on earlier work by
Martin and colleagues. In 2002, they published a paper in Nature that argues
the last common ancestor of today's primates lived some 85 million years ago.
This implies that for 20 million years before dinosaurs became extinct, early
versions of primates also lived and evolved. It challenged the accepted theory
that primates and other mammals didn't really thrive on the planet until
dinosaurs were gone.
After that paper was published, Martin said he expected someone would apply the
new statistical techniques to the question of human evolution, but when no one
did, "We decided to do it ourselves."
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Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily
staff) from materials provided by Field Museum, via EurekAlert!, a service of
AAAS.
Journal Reference:
1. R. D. Wilkinson, M. E. Steiper, C. Soligo, R. D. Martin, Z. Yang, S.
Tavare. Dating Primate Divergences through an Integrated Analysis of
Palaeontological and Molecular Data. Systematic Biology, 2010; DOI:
10.1093/sysbio/syq054
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Field Museum (2010, November 5). New statistical model moves human evolution
back three million years. ScienceDaily. Retrieved November 6, 2010, from
http://www.sciencedaily.com /releases/2010/11/101105124241.htm
Note: If no author is given, the source is cited instead.
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