The logical complementarity of the human sexes has been so recognized in our culture that it has entered our vocabulary in the form of naming various pipe fittings either the male pipe fitting or the female pipe fitting depending upon which one interlocks within the other. When the complementarity of the sexes is breached, injuries and disease may occur as noted above. Therefore, based on the simplest known anatomy and physiology, when dealing with the complementarity of the human sexes, one can simply say, Res ipsa loquitur - the thing speaks for itself!
There's also this, which surely resonates with anyone fortunate enough to have heard James Paxson's paper at Kzoo (see reference here):
"It is absolutely clear that anatomically and physiologically the alimentary and reproductive systems in humans are separate organ systems, i.e., the human does not have a cloaca," he said, referring to the posterior orifice that serves as the one opening for genital, urinary and intestinal tracts in amphibians, birds and reptiles. The surgeon general nominee wrote that "even primitive cultures understand the nature of waste elimination, sexual intercourse and the birth of children. Indeed our own children appear to 'intuitively' understand these facts."
Mostly he's talking about anal sex. Let's put aside the strangeness of his implicit gendering of the anus (my elbow? Male or female?) and put aside (until your comments) his primitivism, and simply wonder: does he read fablieaux? Because I can't help but hear, even from beneath the cotton batting, "Le Chevalier qui fist les cons parler."