I thought the explanation given by "Sprite" was adequate.-1) At one time there was no such thing as sexual reproduction. True but there was reproduction.-2) Sexual reproduction requires two sets of organs/structures. But they can be in the same organism. And they don't have to be very different.-The following goes into detail, but is a bit technical: http://en.wikipedia.org/wiki/Evolution_of_sexual_reproduction-This site ends with the intriguing idea that males are parasites! http://www.evolutionary-philosophy.net/sex.html