Hairy vs. not
From puberty on, men grow much more hair on their bodies and especially their faces than women. This is because sex hormones called androgens stimulate hair growth, and men have more of those hormones.
But what determines the pattern of male hair growth? And in particular, why do men have beards ?
Most psychologists believe beards became prevalent because, women found men with facial hair more attractive to them than men without it, and thus were more likely to mate with bearded men. This attraction could arise because beards not only signal high testosterone levels, they also signify sexual maturity (in much the same way as breasts on women), as well as possibly signifying dominance by increasing the perceived size of a man’s jaws.
On the other side, the same testosterone that sprouts hair all over men’s bodies also leads them to go bald later in life.