How can you people be grossed out by reproduction and mating? If your parenst didn't get it on, then you wouldn't be here. It's thanks to the stupid media that people think sex is such a terrible thing. Well, it's bad to me because it results in more stupid humans being brought into the world.
I once had a theory on Pokemon reproduction. In their wild state, they breed much like real animals, watch a nature show for reference. A female Pokemon has a second womb where a single dormant egg is always kept. Why? I don't know, she just does. Anyway, the only way this egg is fertilized is when breeding occurs in a confined environment, like the daycare center. For some reason, the male and female Pokemon have an urge to breed quickly (maybe the old couple use some sort of drug on them?), and they create a special egg. The male mounts the female and stimulated her to lay this once dormant egg. Once the egg is layed, it is very soft and jelly-like but hardens within moments. The male ejaculates his sperm into the egg and fertilizes it.
This egg is very unusual. It grows to be quite large in a short amount of time as it hardens. The embryo inside developed not from the warmth of a mother's body but from the energy waves caused by the attacks from fighting Pokemon on the outside (hence Elm saying that a Pokemon egg only hatches when in an active party). That's my half-baked theory anyway. It's late.