From what little I can remember from distant hair and beard history, long hair and beard were or were probably seen as manly traits for a long time basically because men are hairy or generally have a higher capacity for hair than women so .. You know, if you were a proper barbarian or berserker viking, sporting a full beard and a long mane was probably masculine and cool.
Then the romans figured out that long hair and beards were a potential weakness in combat because they could be pulled and tugged at by your enemy. Your own beard in your eyes could probably mess up your orientation too. For that reason, their soldiers were clean shaven with short dos and not having a beard became the manly thing.
This is probably not accurate and may even be to a large extent wrong, but either way it's a good story.
Sidewinder, nice picture
