Books: Wiping the floor with the lads in tight genes under the fridge: Woman: an intimate geography by Natalie Angier Little, Brown, pounds 17.99, 432pp

Given half a chance, argues Anna McGrail, women have a better evolutionary reason for sexual promiscuity than men. Given half a chance...

WOMEN "MOSTLY ignore what science has to say to them and about them," says Natalie Angier, Pulitzer-Prize-winning science writer for the New York Times. Hardly surprising, perhaps, if the main conclusion of the biological sciences seems to be that millions of years of evolution have rendered us genetically incapable of reversing into a parking space.

To redress the balance, Angier takes us on a geographical tour of the female body: she guides us through the ecosytem of the vagina, explores the facts and fictions of the breasts and muses upon the metaphors of the menses. She traces our development from a fetus through to the menopause, examining the minute (X chromosome) and the large (our interpretation of ourselves in contemporary history). The question she sets is "What makes a woman?" and she looks for answers in, among other places, physiology, genetics and endocrinology. This is an ambitious book, but we have a guide whose enthusiasm draws us along at an unflagging pace. Assuming her readers will mainly be women, she shouts, "Come on, gals!" and we're off.

New vantage points, even for the stray males at the back, are always refreshing, and these Angier constantly provides. Women seeking medical help to conceive, for example, have found their gametes briskly defined: a woman is born with all the eggs she will ever have and they "degenerate" from then. A man, on the other hand, can produce several thousand new sperm every hour! As Angier points out, "The mere ability to replicate is hardly cause for a standing ovation." It is something within the egg itself, she reminds us, which effected Dolly the sheep, maternal factors which allowed the adult genome to recapitulate itself. The egg holds the secrets of genesis and this may be why women no longer produce new eggs in adulthood. It is not a deficiency, but a sign of our molecular complexity.

Angier throws out theories "like rice at a bride", but each grain challenges the dominant paradigms. Menopause, for example, can be interpreted as an evolutionary necessity. Without grandmothers to get on with the gathering while the hunters were splendidly hunting, homo sapiens would not have had the calorific dowry to invest in intelligence and become very sapiens.

During this adventure, we construct a relief map of liberation biology as we go. Women do not have to be mired in "the sludge of biological determinism." We have choices, especially as to the boundaries of control over our bodies, whether that line is at HRT, abortion or breastfeeding. Nevertheless, this is not so much a tale of X versus Y, although the female body is still a battleground, but a celebration of every woman's glorious anatomy and chemistry. The author's passion for the joyful mysteries of our geography shines through every sentence.

If, in the 1970s, we clutched our copies of Our Bodies, Ourselves and examined our genitals with a mirror, now is the time to praise the vagina as "a pause between the declarative sentence of the outside world and the mutterings of the viscera". We might as well rhapsodise oestrogen as "a structural tone poem" rather than a plain old hormone, as we don't understand how it works.

As Angier strips away the layers of myth that have built up between Galen and Grafenberg, we discover how much of our terrain is unexplored. Some scientific studies into gender differences, our guide points out tartly, are in such a mess that they are "like the floor underneath your refrigerator: you don't want to know". This is a salutary reminder in an age when certain truths are held to be self-evident: that men are programmed to be promiscuous while women sit at home under the influence of the SSEN (Sugar and Spice and Everything Nice) gene and hold out for monogamy.

Such truths are not self-evident when, as Angier does, you "run them through the meat grinder of analysis". A prime determinant of behaviour is the calculation of our best chances of throwing our garland of genes into the future. Reproductively speaking, liaising with a single mate might be a better bet for a male. And if female sexuality is really so feeble, why have societies gone to such lengths to control it, in marriage, purdah, infibulation?

Women do not need to orgasm to reproduce, so why has Nature given us a clitoris? In the past, it may have been much larger, and female primates may have used its erotic energy to take them through multiple sexual encounters with any available males (so that's why it takes us so long!) in a quest for satisfaction. Such behaviour has a Darwinian justification: female promiscuity pays in terms of higher conception rates. Given half a chance, we human females might be as opportunistic as our bonobo or chimpanzee cousins. Given half a chance.

The basis for our behaviour seems to lie less in our genomes than in the ecological circumstances in which that genome expresses itself. Wanton behaviour is not such a useful adaptation any more: it can get you stoned to death. Some evolutionary biologists believe that the clitoris is, in fact, still diminishing from want of use. There's a challenge: can we form a society to save the clitoris? Or shall we just stand here and scream? Come on, gals!