Why does human head hair grow forever?

For some reason at some point in history our ancestor's head hair began to grow indefinately. I think sheep and people are the only beings who have hair that never stops growing.

In sheep it's because they were bred by humans to be that way.

But why is human hair growing forever?

Why does human head hair grow forever?

It doesn't. It's like hair on the rest of our body actually, the follicles turn on and off and when the follicles are off they are off they often fall out, but not always. The only difference is that on our scalps, the follicles don't necessarily shed the hair. But this is similar to some mens beards (some men can't grow beards), The hair of poodles and maltese dogs and many other animals.

Why does human head hair grow forever?

I think that animals who have hair grows them forever too. we grow hair forever because regeneration of cells is as long as we were alive.

Why does human head hair grow forever?

Human hair on the head doesn't grow forever, hence why there are bald people and also why it doesn't continue to grow for much more time after a human dies.