If you about this from the stand point of natural selection, only those who have mutated genes encouraging lots and lots of sex have survived to pass down their genes. Therefore, to go against having sex is like going against a few hundred thousands of years of evolution =) So i would imagine it is quite primitive by our standards and encoded in our genes.
Also, I read that if we had prolonged having sex by about 25-35% (so meaning we mate when we're about 35-45) our (great great great great great)^10 grand children can live about to maybe about 300 =D (Given that our telomerase genes evolve correctly, and given that we even survive that long)