I kind of feel bad for those millions of billions of live sperm cells that are sacrificed so one can fertilize the egg. I understand that they are programmed even to fight off the sperm cells of other contributors, so that seldom do humans ever give birth to two babies from different fathers though it can happen. It is common though in pigs for example to have a litter with several different sires.<quoted text>The perfect birth control is coming. They've figured out how the egg attracts the sperm and now they just need to find a way to block the calcium ion signal.
I guess if a white woman married to a white man and neither have any black genes, and she gives birth to twins, one black and one white, the father will know that he was not the only one involved with her.
They say that as many as one in 400 fraternal twins have two fathers. One needs to be more careful.
Nature has its ways of getting at the truth, so it seems.