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Is human evolution speeding up or slowing down? - Laurence Hurst

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    The Tibetan high plateau lies about
    4500 meters above sea level,
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    with only 60% of the oxygen found below.
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    While visitors and recent settlers
    struggle with altitude sickness,
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    native Tibetans sprint up mountains.
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    This ability comes not from
    training or practice,
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    but from changes to a few genes
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    that allow their bodies to make
    the most of limited oxygen.
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    These differences are apparent from birth—
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    Tibetan babies have, on average, higher
    birthweights, higher oxygen saturation,
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    and are much likelier to survive than
    other babies born in this environment.
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    These genetic changes are estimated to
    have evolved over the last 3,000 years or so,
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    and are ongoing.
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    That may sound like a long time,
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    but would be the fastest an adaptation
    has ever evolved in a human population.
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    It’s clear that human evolution isn’t
    over––so what are other recent changes?
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    And will our technological and scientific
    innovations impact our evolution?
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    In the past few thousand years,
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    many populations have evolved genetic
    adaptations to their local environments.
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    People in Siberia and the high arctic are
    uniquely adapted to survive extreme cold.
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    They’re slower to develop frostbite,
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    and can continue using their hands
    in subzero temperatures
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    much longer than most people.
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    They’ve undergone selection for a higher
    metabolic rate
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    that increases heat production.
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    Further south, the Bajau people of
    southeast Asia can dive 70 meters
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    and stay underwater for
    almost fifteen minutes.
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    Over thousands of years living as nomadic
    hunters at sea,
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    they have genetically-hardwired unusually
    large spleens that act as oxygen stores,
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    enabling them to stay
    underwater for longer—
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    an adaptation similar to that
    of deep diving seals.
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    Though it may seem pedestrian by
    comparison,
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    the ability to drink milk is another such
    adaptation.
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    All mammals can drink their mother’s
    milk as babies.
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    After weaning they switch off the gene
    that allows them to digest milk.
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    But communities in sub-Saharan Africa,
    the middle east and northwest Europe
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    that used cows for milk have seen a
    rapid increase in DNA variants
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    that prevent the gene from switching
    off over the last 7-8000 years.
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    At least in Europe, milk drinking may have
    given people a source of calcium
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    to aid vitamin D production,
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    as they moved north and sunlight,
    the usual source of vitamin D decreased.
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    Though not always in obvious ways,
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    all of these changes improve people’s
    chance of surviving to reproductive age—
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    that’s what drives natural selection,
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    the force behind all these
    evolutionary changes.
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    Modern medicine removes many of these
    selective pressures
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    by keeping us alive when our genes,
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    sometimes combined with infectious
    diseases, would have killed us.
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    Antibiotics, vaccines, clean water and
    good sanitation
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    all make differences between our genes
    less important.
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    Similarly, our ability to cure childhood
    cancers,
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    surgically extract inflamed appendixes,
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    and deliver babies whose mothers
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    have life-threatening
    pregnancy-specific conditions,
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    all tend to stop selection
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    by allowing more people to survive
    to reproductive age.
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    But even if every person on earth has
    access to modern medicine,
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    it won’t spell the end of human evolution.
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    That’s because there are other aspects
    of evolution besides natural selection.
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    Modern medicine makes genetic variation
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    that would have been subject
    to natural selection
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    subject to what’s called
    genetic drift instead.
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    With genetic drift, genetic differences
    vary randomly within a population.
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    On a genetic level, modern medicine
    might actually increase variety,
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    because harmful mutations don’t kill
    people and thus aren’t eliminated.
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    This variation doesn’t necessarily
    translate to observable, or phenotypic,
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    differences among people, however.
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    Researchers have also been investigating
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    whether genetic adaptations to a
    specific environment
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    could appear very quickly through
    epigenetic modification:
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    changes not to genes themselves,
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    but to whether and when certain
    genes are expressed.
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    These changes can happen during a
    lifetime,
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    and may even be passed to offspring—
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    but so far researchers are conflicted
    over whether epigenetic modifications
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    can really persist over many generations
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    and lead to lasting
    changes in populations.”
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    There may also be other contributors to
    human evolution.
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    Modern medicine and technology are
    very new, even compared to the quickest,
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    most recent changes by natural selection—
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    so only time can tell how
    our present will shape our future.
Title:
Is human evolution speeding up or slowing down? - Laurence Hurst
Speaker:
Laurence Hurst
Description:

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Video Language:
English
Team:
closed TED
Project:
TED-Ed
Duration:
05:25

English subtitles

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