Chimpanzees More Diverse than We Thought
11/7/99
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Title: Chimpanzees more diverse than we thought
Source: Reuters
Status: Copyright 1999, contact source for permission to reprint
Date: November 7, 1999
Chimpanzees are far more genetically diverse than human beings are,
researchers said on Thursday, a finding that has implications both
for efforts to conserve endangered chimps and for learning more about
human origins.
A team of German genetic experts said their findings bolster
suggestions that current human populations date back to some sort of
"bottleneck" in evolution just a few hundred thousand years ago.
Henrik Kaessmann and Svante Paabo of the Max-Planck-Institute for
Evolutionary Anthropology in Leipzig, Germany, compared the genes of
both species of chimpanzees, as well as three subspecies.
"The results show a strikingly lower amount of variation in humans
than in chimps," Paabo said in a statement.
"The simplest explanation for this is that at some rather recent
point in the past, humans have been few in numbers. From a genetic
point of view, this point could be the origin of modern humans."
Scientists make comparisons between humans and chimps because they
are our closest cousins, sharing more than 98 percent of our DNA.
All animals have unique variations in genes from individual to
individual. This variation can be meaningless, or can make the
difference in, for instance, susceptibility to disease.
Writing in the journal Science, Kaessmann's team said they examined
genes from the three recognised subspecies of chimps - central
African chimpanzees, western African chimpanzees and Eastern African
chimpanzees.They also looked at bonobos, commonly known as dwarf
chimpanzees.
They looked at one gene called Xq13.3, which is found on the X
chromosome, one of the two chromosomes related to sex. It has no
known function, but it is known to have a low mutation rate and has
been well studied in people.
They found Xq13.3 has almost four times as many variants and is three
times as old in chimps as in humans.
This supports other studies that find humans are extremely closely
related to one another genetically despite what geneticists consider
to be arbitrary designations of "race."
The researchers assumed that chimpanzees and humans diverged from a
common ancestor 5 million years ago, and made comparisons.
It is possible to estimate how long ago the animals in a common
population had a common ancestor by looking at the rate of mutations
in a gene. This is one method used to determine the age of the
"ancestral Eve" from whom all humans are theoretically descended.
This has been done with both humans and chimpanzees using a form of
DNA called mitochondrial DNA. The German team's use of Xq13.3 came up
with different estimates.
They determined that the most common ancestor of chimps lived 1.4
million years ago, while humans can date their genetic Adam and Eve
to just 450,000 years ago.
Mitochondrial DNA research suggests the human Eve lived about 200,000
years ago. Scientists will have to work this all out but Kaessmann
and colleagues said it is the differences between humans and
chimpanzees, not the absolute number of years, that matter in their
work.