[ 2007-03-14 14:41 ]
Goose bumps are a vestige from the days
when humans were covered with hair.
When it's hot and you need to cool down, little muscles at the base of each
hair relax. Your hair becomes relaxed. Your sweat glands pump out body heat in sweat. Your blood vessels
get big to take more heat to the skin to get rid of it. When it's cold, the
arrector muscle pulls the hair up. The duct to
the sweat glands gets small to conserve heat.
Our blood vessels also get small to save heat.
Hair standing up doesn't make very good insulation for we don't have enough fur for that.
Humans don't have very much hair on their bodies anymore. Millions of years ago,
humans probably did. And that hair standing on end helped keep people warmer.
Those little muscles we have on the end of each hair still work. They still make
Cold is not the only thing that can cause our hair to stand on end. Fear or
anger can cause the same reflex. The same is
true for other mammals. You'll notice that on a cat or dog. Their fur gets
bigger when they're angry or afraid.
（英语点津 Annabel 编辑）