A six-year old boy was the only survivor of a sinking ocean liner; he made it to an uninhabited island in the South Pacific and learned to live on his own over the course of the years.
Much later, a fancy yacht sank and a beautiful young woman came swimming up to his island. He pulled her to shore, delighted to finally have some company. She asked him, "How have you gotten along here by yourself?"
"I've found different plants to eat, I dig for clams, and I occasionally can spear a fish in the lagoon"
"How long have you been here?"
"Almost twenty years."
"Well, you probably never even knew about sex, then, did you?"
So she shows him. Afterwards she asked him what he thought about what they'd just accomplished.
He said, "Well, it was just fine, but look at what it did to my clam digger."