women sleep less

Men sleep on subway trains. They sprawl and snore. Women catnap with an eye open because it's a dangerous place for females to drop their guard. That's true of any public place isn't it?

Big fat women sleep on subways, they're invulnerable and generally undesirable to the average predatory male. Old women sleep too, they're just overwhelmed and exhausted by the trial and effort of commuting. But most young girls and women are targets, and there are lots of bad men.