[QUOTE=Johnny Butt;265446]Penis size has something to do with our behaviour with the women. In monogamous relationships penis size doesn't matter. When females mate with 10-20 different partners, the one with the biggest penis size is most likely to pass on his genes because he can drop his sperm deeper into the vagina. This way the penis size can grow through evolution. This is a scientific fact and can easily be seen with monkeys. Gorrilas only have a penis the size of a pinky, because they only have one partner. And a big schlong is not really useful in nature if you're living in the bushes.
Actually since the cervix is only 3-4 inches deep the cock size doesn't matter much in this regard but the amount of ejaculate and the viability of the swimmers does, particularly the amount of precum which acts as a cleanser of other mens' sperm. The hominids would very often mate with several males in succession and the most viable male would pass on his DNA. The cock size is of minimal import in reproduction..