Well, I believe there is or was at some point such a thing as virgin births in mammals, and maybe in the future it may become an evolutionary necessity in order to continue the human race line or any other animal line.
One must wonder why males also have breasts. It isn’t such a stretch of the powers of the mind to consider the possibility.
It may also be that the beginning of the human race began with one seed and not two. Or maybe many of one kind of seed – either many female seeds or many male seeds that reproduced themselves.
One thing is for sure – logically speaking – the caveman or cavewoman didn’t just drop from the sky fully formed as a human.