Sex A User's Guide

BIRDS DO IT, BEES DO IT Sex in the Animal Kingdom Sex is often thought of as an animal activity ("You're a tiger!"), and the animal kingdom is as good a place as any to start a comparative sex education. Evolution has thrown up innumerable sexual variations in the living world. Some creatures, like aphids, manage to do without sex at all and reproduce using a cloning process, while others can't seem to get enough of it, the humble single-celled paramecium evolving (somewhat extravagantly) eight sexes rather than the more usual two. Some creatures (many species of reef-living fish, for example) have distinctly shaky sexual identities and will change gender at the drop of a hat. Others like spiders and bristle worms combine sex with cannibalism. Indeed, compared to many animals, the sex lives of the most infamous human libertines seem positively lackluster. The Naked Ape As might be expected, when compared with animals, human sex lives most closely resemble those of our nearest relatives--the chimpanzees--rather than gorillas and our more distant cousins the monkeys. Gorillas have tiny penises compared to body size; on average they come in at 1 1"4 inches. Orangutans aren't much bigger at 1 1"2 inches, while the relatively small chimps are a whopping 23U4 inches. Humans come out best with an average of 5 1"2 inches, but there seems to be no reason for this relatively huge size; a 2-inch penis would do the job just as well. Gorillas don't need to be well equipped in this respect because a dominant male keeps a harem of females. This means there's very little day-to-day competition with other males. In contrast, chimps live in large groups where females mate with a number of different males every day. Chimps need a relatively large penis and a high volume of sperm production to compete. The sperm acts as a douche, washing out the sperm left by a female's previous lovers. It's the male chimp who produces the most sperm who will father the most children. This is why chimp testicles weigh around 4 ounces each, while the more monogamous humans clock in at only an ounce and a half. Proportionally the largest testes in the primate world belong to the woolly spider monkey. Females of the species have been known to mate as many as eleven times a day when in heat and literally overflow with sperm. This excess is treated as a nutritious snack, and spider monkeys lick it up by the mouthful. Giving Him the Bone An interesting difference between humans and animals is the lack of a human "penis bone," also known as an os penis. The majority of mammals, including bears, cats, dogs, weasels, moles, shrews, and most primates, possess such a bone, and why humans don't is a mystery. The size of these bones varies. Walruses have os bones two feet long, resembling ivory truncheons, while bats have tiny ones. As a rule, fish lack an os bone (which would spoil their streamlined shape), as do most birds (where they'd be an unnecessary weight). Bird Penises Some birds have penises; these are usually found among flightless birds (where the extra weight isn't a disadvantage) and aquatic birds like swans, ducks, and geese (where aquatic mating means there's a chance of sperm being washed away). It's probably a coincidence that penis-owning waterfowl seem to be the ones that most commonly indulge in rape. Male ducks have a reputation for this sort of thing and often take part in "gang bangs"--large numbers of drakes mobbing a female for sex and sometimes drowning her as a consequence. Bird penises tend to resemble mammalian penises but do not contain a urethra to drain the bladder. Some can be remarkably long; the Argentine lake duck commonly has an 8-inch penis, but the largest reach 16 inches. For those who'd like to see one, fresh ostrich penises can be bought over the Internet as an aphrodisiac.Arnott, Stephen is the author of 'Sex A User's Guide' with ISBN 9780385337069 and ISBN 038533706X.