How did this become ordinary all over the world, when did this start? I know that some communities do not fall under this statement, for example: Sikh men keep their hair long, and some other exceptions, but apart from these communities, why is it normal in most of the world for men to have shorter hair and women to have longer hair?
More can be written, but you might like to start with the FAQ section "On men with short hair, women with long hair, and vice versa" (in the app, that's about halfway down) with answers by various people, including /u/chocolatepot, /u/cthulhushrugged, /u/churakaagii, and others.
This is not to discourage discussion. More questions, data and debate are welcome.