system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do people go bald with old age while other animals do not?
gpt
We have two types of hair follicles, vellus follicles and terminal follicles. Most of your skin is covered with vellus follicles, which produce tiny light colored hairs. The only places that have no hair follicles are the lips, palms, soles and parts of the genitalia. Terminal hair follicles develop from vellus hair follicles. During puberty in males, vellus follicles develop into terminal follicles on the face to form the beard. Somehow, aging causes terminal hair follicles on the heads of some men to revert back into vellus follicles. Most other animals just have one type of hair that doesn't go through weird transitions, so their hair follicles don't contain instructions for how to be tiny invisible hairs.