Dear Dr. Tatiana
5th December, 2008
'My boyfriend is the handsomest golden potto I ever saw. He's got beautiful golden fur on his back, creamy white fur on his belly, he smells delicious, and he has ever such dainty hands and feet. There's just one thing.
Please, Dr Tatiana, why is his penis covered with enormous spines?'
Spooked in Gabon
Dear Spooked in Gabon,
All the better to tickle you with, my dear. At least, I’ll bet that’s a big part of the reason. Golden pottos are little-known relations of bush babies: small, night-climbing primates that are distant cousins of monkeys and apes. If you look at your cousins, you’ll see your beloved is not alone. Bush babies and many other primates have monstrous penises: many of them look like medieval torture instruments. They have spikes and knobs and bristles and are often twisted into weird and sinister shapes. By comparison, the human penis is dull, notable only for its girth.
Penises are for more than just sperm delivery, you see. If females mate with a number of males, each subsequent suitor will sire a larger proportion of her children if his sperm are the ones that do the trick. A male who can stimulate his mate to take up more of his sperm, or who can somehow get rid of the sperm of his rivals, will spread more of his genes than less artful fellows. Thus, the ﬁrst consequence of female promiscuity is that males are under great pressure to outdo one another in all aspects of love. For this task, the penis is an important tool.
Consider damselﬂies. These insects, close relations of dragonﬂies, look sweet and innocent as they ﬂit along the riverbanks on a sultry summer day. But they have evolved some of the fanciest penises around. A typical damselﬂy penis has a balloon (an inﬂatable bulb) and two horns at the tip, plus long bristles down the sides. In the black-winged damselﬂy, Calopteryx maculata, the male uses this device to scour sperm from inside a female before depositing his own. But in the related Calopteryx haemorrhoidalis asturica, he uses his penis as an instrument of persuasion: by stimulating his mate in the proper manner, he can induce her to eject sperm from previous lovers. Meanwhile, the moth Olceclostera seraphica has genitals that resemble a musical instrument: the male rubs one part of his privates against another, producing vibrations with which to thrill his mate. In contrast, among termites the female typically mates with only one male – and male termites have plain, unadorned genitalia that do not differ much from one species to the next.
A penis is not the only way to outdo other males, of course. Take the ghost spider crab Inachus phalangium, a creature that lives under the protective tentacles of sea anemones. The male makes a special jelly to seal the sperm of previous males into a corner of the female’s reproductive tract so it won’t be able to mingle with his own. Or consider the dunnock, a bird that looks like a sparrow that has ﬂuffed its feathers in ashes. Most male birds – swans, ducks, and ostriches being exceptions – do not have penises. Instead, males and females copulate by quickly pressing their genital openings together. Hardly satisfactory. But even without a penis, male dunnocks have found a way to get rid of rival sperm. Before sex, the male pecks the nether regions of his mate; sometimes this encourages her to dump any sperm she’s collected. Even more exotic is the red-billed buffalo weaver, an African bird that lives in small communities. The female is wildly promiscuous. Apparently in response, the male has evolved a pseudo-phallus: a rod of tissue that cannot transfer sperm. During sex, he rubs this rod against the female’s genitalia for about half an hour, at which point he ejaculates from his genital opening and appears to have an intense orgasm. The male who provides the most vigorous stimulation is presumably the most successful at persuading a female to use his sperm.
All of this provides a clue as to why your friend’s penis looks so alarming. Among primates, as among insects, it is a rule of thumb that in species where females consort with one male at a time, penises are small and uninteresting. I mean, take the gorilla: a huge guy with a little teeny weenie. A male gorilla can weigh 210 kilograms (460 pounds), but his penis is a measly ﬁve centimeters (two inches) long and entirely devoid of knobs and spikes. The Argentine lake duck puts him to shame. The duck is small, but his penis, which rivals that of the ostrich, is 20 centimeters (eight inches) long – and it has spines. But then, a male gorilla generally presides over a small group and does not often have to worry about other fellows’ sperm. If I were a girl gorilla, though, I’d feel I was missing out: as far as anyone can tell, the females of more promiscuous primate species are more capable of orgasm. So I’d guess your mate’s penis is gloriously bespined because female golden pottos sometimes sleep around. But whether the spines have evolved because you like them, or whether they are more for scrubbing: well, why don’t you ﬁnd out?
■ Extracted from Dr. Tatiana’s Sex Advice to all Creation by Olivia Judson, published by Vintage at £7.99. Copyright Olivia Judson, 2002
This article first appeared in the Ecologist May 2005