I have never been able to figure out if it is random mutation how did it become the norm? And how did everything become male and female if it was all random? The male and female would seem to be a very chancy way to go what if something became a male and there were no females to mate with or vise versa. Seem like a very chancy way to go, why was everything and why is everything not self replicating? Seems like that would be the best way to ensure a mutation to survive.
Males and Females have something that hermaphrodites will never have though, sexual specialization, division of labor, sexual selection, and sexual dimorphism leading to mostly non overlapping prey determination.