This one comes via a friend who recently shared this vexing question.
The subject is human hair and its apparent intelligence, for lack of a better word.
Let's take the hair on one's arm, for the sake of illustration.
The hair begins to grow at some point, reaches it's prescribed length, determined through centuries of evolution and dictated by it's location on the body.
So it's reached it's length and somehow knows when it's time to stop growning.
How does it know when it's reached it's prescribed length and to stop growing at that point?
My wild guess would be something to do with hormonal signals. But that's not the real question here. It gets better.
Now say that you accidentally singe off a patch of hair on your arm. Or for some reason it gets shaved off.
Here's the real mystery.
How do individual hairs:
A. Tell that it's been cut or burned off, and
B. What causes the hair to then begin growing again until it reaches its set length, and then stop growing?
Being perpetually curious, this one has me utterly stumped. I'd bet that biological science has solved this one, though I've never learned the answer.
Any of my many learned readers care to speculate as to how our hair appears to have a mind of its own? Or better yet, provide a plausible answer?