Beard 胡须

A beard is the collection of hair that grows on the chin and cheeks of humans and some non-human animals. In humans, usually only pubescent or adult males are able to grow beards. From an evolutionary viewpoint the beard is a part of the broader category of androgenic hair. It is a vestigial trait from a time when humans had hair on their face and entire body like the hair on gorillas. Since hair bore parasitic bugs and ticks, as humans evolved they lost more hair, due to the advantage that a more glabrous body prevented parasitic bugs. The evolutionary loss of hair is pronounced in some populations such as indigenous Americans and some east Asian populations, who have less facial hair, whereas Caucasians and the Ainu have more facial hair. Women with hirsutism, a hormonal condition of excessive hairiness, may develop a beard.