According to a study published in Evolution and Human Behavior, you have a helmet at the tip of your penis so your thrusting can eject your rivals' sperm. To prove the theory, a team lead by Dr. Gordon Gallup of the State University of New York devised a test using latex penises, an artificial vagina, and starch and water. They discovered that the penis's coronal ridge -- the point where the head meets the shaft -- can pick up and carry out of the vagina as much as 90% of the cornstarch mixture with a single thrust. A penis without a coronal ridge (who would that be?) only removed 35% of the cornstarch. In addition, to be a real man and get rid of that other guy's semen, you have to thrust deep. A mincing three-quarter thrust removed only 40% of the cornstarch. Finally, to neatly wrap up the theory, the researchers discovered that sex tends to be more energetic if the guy suspects the woman of cheating. Here's the full argument -- and the opinions of those who think it's high quackery, on the BBC:
http://newsvote.bbc.co.uk/mpapps/pag...s.bbc.co.uk/2/
hi/health/3128753.stm
Sure, but he didn't ejaculate cornstarch, did he? He ejaculated a hundred million little bastards who have a head start on me, damnit!