What is the EVOLUTIONARY ADVANTAGE...

of masturbation?

Actually there is more than one. People who rise foxes know that when you mate foxes you have to let them copulate for 2 weeks, because the sperm is very low quality at the beginning. So maybe men which are not copulating are masturbating in order to have fresh sperm ready to inseminate female right away.
The other would be to make sure you don't try to fuck a wife of a big guy on his eyes.
Actually there might be even some evolutionary advantage of homosexualism. There is a species of fish in which some males look like females and inseminate eggs of females while true males think they are just females.

to orgasm without the use of useless human beings. :/

http://www.iwantapal.com/

Do humans instinctively know how to have sex? Or have we become dependant on culture?

>>5
Moron thinks all that exists is instincts and environment. That's funny, that's what animals think too. :/
MOOOOoooooooOOOOO!!!

>>6
listen here, jerkface