You've come a long way, baby, was the mantra of 1970s Cosmo girls. Though the fact that the first British Cosmo editor, Marcelle D'Argy Smith, has written yet another sex manual, The Lovers' Guide: What Women Really Want, does suggest that the primrose path of dalliance demands regular re-paving. It seems rather dispiriting that Ms D'Argy Smith still considers that there are potential lotharios willing to pay GBP 14.99 for a glossy hardback book with lots of soft-toned soft-porn photographs, who need to be told that, "women expect men to have clean underpants" and "teddy bears have no place in the beds of adult men".

Yet, into this murky landscape a clear, bright beam of light has shone. For next week sees the publication of the ultimate sex guide. And I do mean ultimate. Dr Tatiana's Sex Advice to All Creation is the sort of comprehensive work which may very well have saved the dinosaurs if only they'd had the foresight to learn English.

Author Olivia Judson, aka Dr Tatiana - the Dr Ruth of wilderness, jungle and ocean - answers the sex problems of an astonishing array of species, from marine iguanas to bronze-winged jacanas, lionesses to yellow dung flies: every organism baffled by the battle of the sexes and hungry for her advice. A load of anthropomorphous twaddle? Perhaps. But the breadth of scientific information and its hilarious parallels to the fumblings of homo sapiens make this the sex guide for the connoisseur.

Want to refute those allegations that only humans indulge in homosexuality? Dr Tatiana has all the evidence. Need to know the best time for a sex change, how to organise a virgin birth, or applaud the benefits of a detachable penis? It's all here - a cosmic orgy that would make Caligula look like a choirboy.

Studying this universal sex fest was no more than an obvious career choice for Dr Tatiana, she says. "Quite simply, I decided to dedicate myself to sex when I realised that nothing in life is more important, more interesting - or more troublesome. If not for sex, much of what is flamboyant and beautiful in nature would not exist. Plants would not bloom. Birds would not sing. Deer would not sprout antlers."

Thus, via Stanford University and a PhD in biological sciences from Oxford, Olivia Judson took up a research fellowship at Imperial College, London, and began her meticulous interrogation of the birds and the bees. "For most of us, caught up in the hurly-burly of our daily struggles, the purpose of life may seem elusive" she observes. "But from an evolutionary point of view, the purposes of life are clear:
survival and reproduction. If you fail at either, your genes go to the grave."

No exchange of genes, no genetic variation. No genetic variation, no evolution. So, the outcome of next Saturday's mating attempts in Acacia Avenue, or under a rock on the Galapagos Islands are equally crucial. The need to find and seduce a mate is one of life's most powerful forces.

The most powerful, if you happen to be a Freudian, the most fascinating if you have taken the pen name Tatiana. For "nothing in life generates a more ecstatic diversity of tactics and stratagems." And the battle of the sexes is no myth, warns the doctor. It is eternal war. "And this battle erupts, because, in most species, girls are wanton."

So, the anguished plea from an exhausted stick insect that she has been copulating with her mate for ten weeks and is now horribly bored and convinced that her lover is insane, is answered with all the tact that a decent agony aunt must display. Yes, it must be wearisome, she agrees, but the tiny male stick insect - only half the length of the female - clings on to ensure no other males can get near .

A shrewd decision, because she would be very unlikely to discourage an approach. Like most females, she's a bit of a slut, and like most males, he is determined that his genes will survive.

The confusion about the relative promiscuity of males and females dates back to 1948 and experiments with fruit flies, performed by a scientist called Bateman. Keeping an equal number of male and female flies in jars for a few days, Bateman observed that the males were keen to mate as often as possible, while the females rejected the majority of advances.

He explained this by noting that males produce lots of tiny, cheap sperm, while females produce a few large, valuable eggs. Thus, he argued, males are limited in their reproduction only by the number of females they can seduce; females by the number of eggs they can produce. Hence males are natural philanderers while females are naturally chaste.

Sadly, for the moral reputation of the female, Bateman was wrong. "In the 1980s, the development of more sophisticated genetic techniques meant that biologists could find out who was having whose children. And they discovered something that no-one had predicted. Namely that from stick insects to chimpanzees, females are hardly ever faithful."

Even more surprising, they benefit from promiscuity.

So, we owe some sympathy to the worn-out Serengeti lion, who laments,"my lioness is a nymphomaniac. Every time she comes into heat, she wants sex at least every half an hour for four or five days and nights", even if Dr Tatiana is a little dismissive of his exhaustion. "A great big lion like you should be able to keep it up without fussing," she chides, adding that she has heard of lions copulating 157 times in 55 hours. The reason is clinical. The lioness needs a great deal of stimulation to get pregnant. Less than one per cent of copulations produce cubs, and so she is programmed to keep at it, as are female rats, golden hamsters and cactus mice.

At least the lion does not have to worry about bringing the Serengeti equivalent of candy. For the long-tailed dance fly, this is a must. "In long -tailed dance-fly culture, it's traditional to mix food and sex. An hour before sunset, the male captures a suitable insect - a juicy may-fly, perhaps - and then goes to find a female, so she can eat it while they make love."

Females congregate in forest clearings to await the males, their bodies silhouetted against the sky. They know that the males always go for the girls with the biggest attributes, and so they assist their chances in an unusual way.

"They have two inflatable sacs, one on each side if the abdomen. Before joining the party, a female sits on a bush, gulping air and blowing herself up to three or four times her normal girth." No wonder she's called a dance fly. Lining up for the boys, exaggerating her bosom ... she might as well be a school dance fly.

But it is not principally the male who demands a perfect physique in his mate, according to Judson. "Girls may say they want a kind, sensitive, devoted guy - that personality matters more than looks - but the truth is, in many species, females are body fascists. That's why, as a rule, it's the males who have ridiculously long tails, or
fancy head-dresses, despite the obviously greater risk of being eaten." Darwin concluded that in sexual selection, the preferences of the female are rewarded, and females like big, gaudy ornaments - sort of feathery Ferraris.

Like all good sex therapists, Dr Tatiana prefers to offer reassurance where possible. So she is able to tell an irate female marine iguana that masturbation is not unhealthy, indeed, in young iguanas, it is positively beneficial.

"Look at it from the guy's point of view," she suggests. "Here he is, a tasteful shade of red, his spiky crest a full 20 centimetres from his crown to his tail - he's ready to go, desperate to use one or other of his penises (yes, like many reptiles, he has two, a left and a right). But being young and therefore small, he doesn't have much of a chance. It isn't just that the ladies prefer to mate with bigger, older males. It's that even if he mounts a female, the odds are he'll be shoved aside by a bigger fellow before he climaxes. That's why the young males masturbate when they see a girl go by.