RD201906

(avery) #1

Science


Knows Why ...



  1. You get goose bumps. When you
    feel a chill or see something scary,
    your body releases a surge of adrena-
    line. The point is to make your body
    hair stand up—which helped our
    animal ancestors stay warm and also
    made them look larger in the face of
    predators. Getting those individual
    hairs to stand at attention requires
    the teeny skin muscles at the base of
    each follicle to contract, making your
    skin look vaguely like a goose’s post-
    plucking—hence, goose bumps.

  2. You grow wisdom teeth. Wisdom
    teeth are actually a third set of mo-
    lars. They allowed our forebearers to
    munch on rough food such as roots,
    nuts, and meat, especially when other
    teeth fell out (alas, our ancestors had
    poor oral hygiene). About 35 percent
    of people never develop wisdom teeth,
    partly because of an evolutionary shift
    that means the human jaw is often too
    small for them. The rest of us start de-
    veloping them by age ten, though they
    don’t fully emerge until young adult-
    hood, which is when we (allegedly)
    acquire full-grown wisdom.


3.Your fingers and toes wrinkle in
water. When you’re in the bath, water
seeping into your skin makes the up-
per layers swell. That causes the blood

vessels below to constrict, which in
turn causes some of the upper lay-
ers of skin to collapse. The irregular
pattern of swelling and falling skin is
what we see as wrinkles on our finger-
tips and toes.


  1. Your knees crack after sitting for
    a long time. The sounds you hear
    are probably caused by gas being re-
    leased from the spaces between your
    joints—just like when you crack your
    knuckles. Meanwhile, muscles or ten-
    dons rubbing against your bones may
    also make your joints creaky. “We say
    motion is lotion,” Kim L. Stearns, MD,
    an orthopedic surgeon at Lutheran


Reader’s Digest


58 june 2019


No.

5
What
Gives
Yo u a
Stitch
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