[情報] First chimp fossil unearthed
http://www.nature.com/news/2005/050829/full/050829-10.html
http://www.nature.com/news/2005/050829/pf/050829-10_pf.html
Published online: 31 August 2005; | doi:10.1038/news050829-10
First chimp fossil unearthed
500,000-year-old teeth shed light on evolutionary split between humans and
chimps.
Michael Hopkin
Sally McBrearty unearthed some chimp teeth where no one expected to find
them. (c) Andrew Hill
Palaeontologists digging in the dusty wastelands of East Africa have
discovered the first known chimpanzee fossil. The modest haul of just three
teeth is the first hard evidence of the evolutionary path that led to today'
s chimpanzees.
As well as shedding light on chimps, the find throws up new questions about
human evolution; it seems that chimpanzees may not have been physically
separated from humans as was once thought.
That no one had previously found a chimpanzee fossil had long been a
frustrating puzzle, comments Sally McBrearty, an anthropologist at the
University of Connecticut, who made the find near Lake Baringo, Kenya, with
her colleague Nina Jablonski. Set against the many human fossils found in East
Africa, the lack of specimens documenting the chimp's evolutionary story was
exasperating.
Part of the problem, McBrearty explains, is that chimps tend to live in hot,
wet jungle conditions that are not good for the preservation of remains.
Humans, on the other hand, are thought to have lived for millennia on the
savannah, where bones are less likely to rot.
The great divide
Previous theories suggested that chimps never crossed east of the Rift Valley,
but instead stayed in the jungles of western and central Africa. Some even
suspected that this physical separation was what set the earliest chimp and
human ancestors on contrasting evolutionary voyages. But now McBrearty has
stumbled on chimp remains east of this divide.
No one was looking for chimps here.
Sally McBrearty
University of Connecticut
This means we need a better explanation of why and how chimps and humans
went their separate evolutionary ways, McBrearty says. The discovery that
chimps were living in semi-arid conditions as well as in the jungle seems to
blow apart the simplistic idea that it was the shift to savannah that led to
humans walking upright.
The teeth are around 500,000 years old, McBrearty and Jablonski report in
Nature1. So far it is impossible to say whether they belonged to the same
species as modern chimps, Pan troglodytes, or to some unnamed, now extinct
ancestor. "It wouldn't surprise me if there are lots of extinct chimp
species," McBrearty says.
If the teeth do belong to the same species as modern chimps, this would mean
the species is quite long-lived. In contrast, modern Homo sapiens has been
around for only some 200,000 years. But the earlier human species H. erectus
is thought to have lasted around a million years.
Finding the ancestor
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The fossils are not old enough to tell us about the common ancestor of
chimps and humans, which lived between five and seven million years ago,
points out anthropologist Daniel Lieberman of Harvard University in Cambridge,
Massachusetts. "But this raises hope that we can find older stuff," he adds.
McBrearty suspects that although there may have been more chimps living in the
jungles of western Africa, there are probably more fossils in the dry
eastern savannah. It's just that "no one was looking for them" she says.
McBrearty hopes to return to Kenya in December to resume the search. In
spite of the baking equatorial heat, December's dryness makes it the best time
to probe for delicate remains.
References
1. McBrearty S. & Jablonsk N. G. Nature, 437. 105 - 105 (2005). | Article |
PubMed |
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