In the beginning all babies are hairy, covered in a soft light down called vellus hair. Once we hit puberty everything changes. The sex hormones arrive. Androgens are present in both sexes, and cause hair in puberty to become darker and thicken in the pubic areas and under armpits. Men have more androgens than women and additionally find hair sprouting on their chest, upper lip and face.
According to Darwin’s theories, animals, including humans, evolve features to attract the opposite sex and intimidate rivals of the same sex. So like lions with large manes and male peacocks with splendid arrays of feathers, men with big beards must have looked sexy and dangerous to our neolithic ancestors.
Meanwhile, women lacking facial hair have been naturally selected for in the process of evolution.
Bonus fact: If a man never shaves his beard it can grow up to 30 feet long during his lifetime.
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