It shouldn't be surprising, really. When it comes to sex, we'll hit on anything to get off. Vegetables, clothing, alternate body parts, glory holes, elaborate toys of all materials and other substitutes far too mind-blowing to consider: all are fair game for the human animal to toy with.
evidence has been revealed in support of the theory that humans (homo sapiens) cross-bred with neanderthals and other species of early man. Anyone who has ever seen Quest for Fire with it's impromptu scene of doggy-style cavemen humping could have told you that, but now at least we have DNA proof.
Goes to show how adaptable we are at fulfilling a need any way we can. Face it, our ancestors were as much pervs as we are today. After all, we're only human.