Fwd: Perpetual change

From: Wade T.Smith (wade_smith@harvard.edu)
Date: Fri Apr 27 2001 - 14:29:05 BST

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    My apologies if this has been posted before-

    - Wade


    Perpetual change

    Have humans stopped evolving? No, say scientists studying key life events
    in twins.

    Humans are still evolving, according to new research that contradicts the
    prevailing view that modern society's healthcare and technology means
    human populations are not changing genetically.

    In particular, the scientists say that, in industrialised societies,
    behavioural traits that cause women to have children earlier are becoming
    more common.

    Ian Owens from Imperial College in London and his colleagues used data
    about the lives of 2710 female twins in Australia to calculate the
    evolutionary "fitness" of each woman - a measure of the number of
    descendants her lineage would leave.

    Cultural factors such as religion and education had a big impact on
    fitness, but they could not explain everything. "If you remove everything
    that's cultural, there's still an enormous difference between women,"
    says Owens. He estimates that while 50 to 60% of fitness is
    environmentally determined, 40 to 50% of it is genetic.

    Gene spread

    This finding is crucial because genes that increase the number of
    descendants an individual leaves are bound to become more widespread with
    each generation.

    In societies without medicine or technology, factors such as surviving
    through childhood and resistance to illness are important in determining
    fitness. Genes that diminish the physical ability to have lots of
    children are weeded out by natural selection.

    With better medical care, that kind of selection has been much reduced.
    Instead natural selection is now acting on other factors, such as how
    many children we choose to have, the new research suggests.

    Sarah Blaffer Hrdy, an evolutionary biologist from the University of
    California in San Diego, says the work is "extremely provocative", while
    her colleague Christopher Wills is excited too. "Data on the heritability
    of fitness traits in industrialised human populations are very unusual
    indeed," he says.

    Religion and education

    To find out which genes were involved, the researchers looked at the
    different traits that affected fitness, to see if any of them were
    inherited. They worked out how much was due to genes by comparing data
    from identical twins, who share all of their DNA, with non-identical
    twins, who share only half of it.

    Cultural factors such as religion and education had virtually no genetic
    component. But one major determinant which did was the age at which women
    started having children. The earlier women had their first child, the
    "fitter" they were. This makes sense - women who have their first child
    early have more time to have more children, and a shorter generation time
    also means more descendants.

    The surprise was that across all groups in society, the age at which
    women had their first child was genetically inherited. After accounting
    for cultural factors, 23% of the variation in age was down to genes.

    Owens says the genes involved probably determine psychological or
    behavioural traits that make women more likely to start having children
    younger. He warns that while society is encouraging women to have
    children later, the biological urge to have kids early will get stronger.

    "The genes are pushing in the other direction," he says. "There's a
    fierce conflict between career, and wanting to reproduce."

    More at: Evolution (vol 55 p 423)

    Correspondence about this story should be directed to

    1307 GMT, 24 April 2001

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