He had to ask – and so, as delicately as possible, I’ll try and recount Jesse Bering’s thoughts on the styling and functionality of the human penis. First off, it is pretty big, at least compared to the privates of other apes. Even more curious is the indented cuff below the penis head. Why is the human penis so big, with such ornate features, Bering wonders?

Bering’s mentor, Gordon Gallup, came up with an explanation after experimenting with a polyurethane vagina bought from a sex shop, a collection of facsimile penises and a bowl of cornflour batter designed to simulate sperm. Working feverishly, Gallup proved that if used as a plunger, a human penis is capable of cleaning out more than 90 per cent of sperm deposited inside the vaginal canal by a previous partner, far more than any other penis design. Gallup speculates that the penis evolved its shape because it lessened the chances of one becoming the unwitting surrogate father to another man’s kid.