A Moment of Science  Skinny Legs and All   Why do horses have
skinny legs?  Okay, they aren’t entirely skinny — it’s mostly
the bottom half, with a big muscle up at the top. But that’s
odd. Human legs are kind of like that too — bigger on the top
half. Come to think of it, dogs’ legs are like that. And cat
legs. Wait a minute. Deer legs are really skinny on the bottom
and much thicker at the top. Antelopes. Gazelles. Giraffes.
Elephants.  No, wait. Elephant legs aren’t really like that.
Neither are duck legs, or panda bear legs. So it can’t be a
prerequisite for any leg. What’s the use of a skinny leg?
Answer? Running. The skinniest lower legs belong to the fastest
runners. Why?  It’s because when you run, or indeed walk, you
are constantly swinging the bottom halves of your legs. For
humans, one foot is stopped and essentially resting on the
ground while the other is moving twice as fast as your overall
speed. Then that foot stops and the other one accelerates. And
so on.  Thinner, lighter things are easier