- For the last 6 million years, humans
or their ancestors have been quickly developing flaws in their genes, a
new study says. But they've apparently removed some of the build-up through
sex.
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- Every newborn over that time span has
had an average of two or three new harmful mutations, researchers calculated.
Such flaws don't cause disease, though they detract from a person's overall
fitness, said the study published in Thursday's issue of the journal Nature.
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- The study done by Adam Eyre-Walker of
the University of Sussex in England and Peter Keightley of the University
of Edinburgh in Scotland offers the first reliable estimates on such mutations,
said gene expert James F. Crow of the University of Wisconsin in Madison.
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- He said in a telephone interview that
the estimated flaw rate is surprisingly high and implies "a rather
large load (of flaws) for us to be dealing with."
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- So how has the human race survived all
that pollution in the gene pool?
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- Some mutations have apparently been eliminated
by people who carry them never having offspring, the researchers said.
Flaws that remain might be too minor to make a real difference.
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- Keightley speculated that human ancestors
who carried the most flaws were least likely to have children. That would
eliminate mutations in batches and might still be going on today.
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- Crow said the new work strengthens the
argument that most organisms reproduce sexually because it lets them get
rid of gene flaws more efficiently.
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- Modern medicine, by saving lives and
overcoming infertility, lets people reproduce now who couldn't have in
the past. So it presumably lets more bad mutations live on.
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- Does this mean the human race will become
dangerously loaded down with genetic flaws? Don't worry, Keightley and
Crow said.
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- "I think it's something to think
about, but it has an awfully long fuse," Crow said.
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- The mutations almost certainly have very
tiny effects, such as a predisposition to headaches, stomach upsets and
weak eyesight, especially later in life. It would take centuries or thousands
of years of modern health care to build up to a significant level of harm,
Crow said.
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- The researchers calculated the rate of
new deleterious mutations by looking for differences in the details of
46 genes in humans and chimpanzees. That let them estimate rates of mutation
since the evolutionary split between the ancestors of people and of chimps.
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