For all species, the bottom line to being an evolutionary success story is making lots of babies that survive to become adults, which in turn reproduce.

Olivia Judson, an evolutionary biologist at Imperial College in London, details the many ways in which this can be accomplished in her book Dr. Tatiana's Sex Advice to All Creation (Metropolitan Books, 2002).

Judson, in the guise of her alter ego, Dr. Tatiana, has done the impossible: She's written a deeply researched science book on an enormously important topic—the evolutionary biology of sex—that makes you laugh out loud. Frequently.

Oops, I Swallowed My Husband

A green spoon worm, distressed because she accidentally inhaled her husband, is another fan looking for advice.

Once again, Dr. Tatiana is able to allay her writer's fears: He wanted to be snuffled and he's not coming back, she says. Her hubby is now resting comfortably inside her, in a special chamber called the androecium—literally, the "small man room." There he will spend the rest of his life fertilizing passing eggs.

"It's amazing how diverse nature is, and the diversity of behavior that's evolved," Judson says in a phone interview. "You'll hear it time and again, at dinner parties and such, that something is or isn't natural. You'd be surprised."

She's not kidding. There are creatures that do it hanging upside down, creatures with their sexual equipment on their heads and in their mouths, those that inject their sperm into females and others that leave it on the ground.

The male Caribbean reef squid places his sperm packet anywhere on the female's head or tentacles. She either moves it to her sperm storage organ or heaves it, depending on her mood—or perhaps on whether she considers him handsome.

There are creatures that do it with their sisters in their mother's belly—these males come to a bad end. The mother's belly explodes, the sisters leave on the backs of passing beetles, and the males die, never having really lived.

There are dads who incubate their babies in their mouths, their vocal sacs, and in pouches. And there are species that use very few males, or none at all.

Choose Me, Choose Me

When there is very little competition among males, as is the case in many species in which there is a profound difference in size between males and females, the male's equipment is decidedly non-flamboyant.

A male gorilla, for instance, weighing 460 pounds (210 kilos), has a two-inch-long (five-centimeter-long) penis, with no knobs, spines, hooks, or other accoutrements on it. In contrast, the Argentine lake duck, which is about 16 inches from beak to tail, has a penis eight inches (20 centimeters) long and with spines. But then, his girls sleep around a lot.

It's when the competition is stiff that the strategies to find, impress, and seduce a mate become far more elaborate, says Judson.

Brilliant feathers, huge antlers, beautiful songs, food, territory, and protection, being the biggest or the baddest or both—these are just a few of the gambits males use in their quest to mate.

The battle isn't won, though, just by depositing sperm. Males need to ensure that it's their sperm that a female uses.

There are lots of versions of the medieval chastity belt, although most don't require the ultimate sacrifice that the male honeybee makes.

The males of many species manufacture a form of cement or glue to try to prevent other males from copulating with a female by plugging up her reproductive tract. Some species have evolved penises with brushes, hooks, spines, or other structures that scrub the vaginal tract clean of a prior suitor's sperm, or stimulate the female into rejecting the sperm of prior suitors.

"Sick of Sex in India," a stick insect, complains to Dr. Tatiana that her lover has been copulating with her for ten weeks, a strategy that the good doctor explains will prevent other males from mating with her.

Most birds don't have penises, but the male red-billed buffalo weaver has evolved a false penis to give him an edge in dealing with the famously promiscuous females of his species. The false penis enables him to stimulate the female before he ejaculates, the assumption being that he who gives the best sex gets to fertilize the most eggs.

When males are scarce, or when a female doesn't want to share her man or wants more than one, the girls in a species can get very nasty—smashing the eggs of a rival, chasing or fighting her or stealing sperm. All's fair in love and war.

"I'm not sure nature is where we want to be drawing our morals from," laughs Judson.

Why They Do the Things They Do

There's a common belief that in most species, the males are philanderers and the females are chaste. Men, the reasoning goes, do better from an evolutionary standpoint impregnating lots of females, while females are more successful with one mate.

Dr. Tatiana puts the kibosh on that theory in a big way.

It's only since the 1980s, with the advent of genetic testing, she says, that scientists began to realize how promiscuous the females of many species are. And only since the late '80s have experts considered the possibility that females are promiscuous because it's beneficial to them. Before then, female promiscuity was generally regarded as unnatural.

But a growing accumulation of scientific data has shown that in many species, females that mate with several lovers produce more and healthier offspring than females with fewer encounters. Conversely, it doesn't do a male a lot of good to bed a lot of females if none of them use his sperm, so he's better off if she mates only with him.

This tug of war between the self-interest of each is at the crux of the battle of the sexes in the evolutionary war: He evolves to control her; she evolves to resist. He develops the capability to insert a plug; she develops the ability to pull it.

As Dr. Tatiana might say, sound familiar?

As advisor to the lovelorn, Dr. Tatiana entertains questions not only from birds, insects, mammals, and other animals, but also from plants, molds, and bacteria. And she covers the gamut of sexual practices.

"I Like 'Em Headless in Lisbon," a female European praying mantis, writes: "I notice I enjoy sex more when I bite my lovers' heads off first. When I decapitate them, they go into the most thrilling spasms."

Dr. Tatiana advises her lovers that the first rule when making love to a cannibal is: Never get eaten during foreplay. Beyond that, she urges the practice of "safe sex": Stealthy Approach, Forceful Embrace, Swift EXit.

She also cautions "Like 'Em Headless" that eating all the males around is not a good idea in times of scarcity.

In the final chapter of the book, Miss Philodina roseola, a microscopic animal whose ancestors abolished men, makes an appearance on Dr. Tatiana's television show, a sort of Oprah for all creatures.

Miss Philodina claims to be thriving despite not having had sex for 85 million years. The studio audience is skeptical, to say the least.

Most species that have done away with men completely quickly reached an evolutionary dead end; too many bad things can happen if you're just endlessly cloning yourself. The fact that "Miss Philodina" has been able to do it successfully causes considerable anxiety among the males in the studio audience.

And then there are the practices of the hermaphrodites, species in which individuals are both male and female and sometimes take turns being each—one day spewing eggs, the next day sperm. In desperate times—say, no suitable mates are available—they fertilize themselves.

"Selfing" Dr. Tatiana calls it—one more interesting concept in a book that's endlessly fascinating and amusing.

Following are related National Geographic news stories:

Evolutionary Oddities: Duck Sex Organ, Lizard Tongue

Study Links Origin of Sexual Reproduction With High Mutation Rates

Fluorescent Feathers Give Parrots Added Allure in Courtship, Study Finds

"Sexually Antagonistic" Bugs Evolve New Weapons

Human Noise May Disturb Whales' "Love Songs"