January 27, 1999
Humans may be collecting bad genes
Humans may be collecting bad genes
Humans could be getting weaker and sicker with each new generation
because of a build up of bad genes.
Most animals weed out harmful genetic mutations by natural selection -
only the fittest survive long enough to reproduce.
But in humans the weak have been prevented from dying out by
improvements in standards of living and health care.
Commenting on the research published in Nature, James Crow, from the
University of Wisconsin in Madison, said it was
likely that in this situation natural selection would "weed out
mutations more slowly than they accumulate".
He said: "Are some of our headaches, stomach upsets, weak eyesight and
other ailments the result of mutation
accumulation? Probably, but in our present state of knowledge we can
only speculate."
Geneticists Adam Eyre-Walker, from the University of Sussex in Brighton,
and Peter Keightley, from the University of
Edinburgh carried out the new research. They calculated the rate at
which human genes have mutated since our
ancestors split from chimpanzees six million years ago.
Keightley told the BBC: "We estimate that about 4.2 new mutations have
occurred on average every generation in the
human lineage since we diverged from the chimpanzees, and that 1.6 of
those are deleterious."
That rate is so high that without other factors intervening the human
race should be extinct by now.
One possible reason that humans have survived is that in the past
natural selection eliminated handfuls of harmful genes
because individuals with lots of mutations died early, before
reproducing.
But it is also likely that genes which were only slightly harmful became
"fixed" in successive generations. Over time these
would accumulate, especially if improving living standards and health
care meant that the harmful genes were less of a
handicap for survival.
--
Judith Richards, London, Ontario, Canada
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