RD201906

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.

4. 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