The art of procreation and the members employed therein are so repulsive, that if it were not for the beauty of the faces and the adornments of the actors and the pent-up impulse, nature would lose the human species. – Leonardo da Vinci

[T]he common thread that binds nearly all animal species seems to be that males are willing to abandon all sense and decorum, even to risk their lives, in the frantic quest for sex. – Randy Thornhill and Craig T. Palmer