Love and romance? It's all in your chemistry

Science is close to explaining the last great mystery of the universe. Anthea Milnes finds out what really makes your heart race

Ever felt bemused by the volume of popular wisdom about love, sex and intimate relationships? Ever wondered how much of it has value in the real world, as opposed to in the realms of fantasy and social cliché. From the hairdressers to the House of Commons, everyone seems to have something to say: men can't commit; women can't wait to commit; women want a boyfriend with a BMW; men want an adoring 20-year-old to hang on their arm; women wear their hearts on their sleeves; men hide theirs in caves on the planet Mars; and love is... er...

Garth Fletcher is director of the International Society for the Study of Personal Relationships and Professor of Psychology at the University of Canterbury, New Zealand. He is also the author of a new book that looks at what psychology can tell us about relationships. If anyone is qualified to act as a scientific guide through the maze that is male-female relationships and to tell us, definitively, what love is, then Professor Fletcher is the man.

"Lots of people," he says, "like to think of romantic love as mysterious, magical and impossible to measure; but in fact, falling in love is one of the most thoroughly investigated and well-understood phenomena in the field of relationship science." The professor is adamant that – contrary to the view of those postmodernists who insist that "love" is solely a Western, first-world obsession, a cultural creation that we have all bought into willy-nilly – love is a basic emotion found in virtually every culture and has biological components that are shared with other mammals.

Full-blooded love is made up of three key components: attachment or intimacy; caring or commitment; and lust. It has its own chemistry. The hallmark hormones of attachment and caring are oxytocin and vasopressin. Both are associated with mother-infant bonding and lactation, but men have them too, and they are produced during sex. Lust, meanwhile, is associated with hormones such as testosterone, also present in both men and women, and spiced up in the heat of the moment by rushes of adrenalin.

Roy Baumeister of Case Western Reserve University, a psychologist whose areas of expertise include sexuality and emotion, agrees with Professor Fletcher, but adds tellingly that, "the modern West has given love more recognition as a vital form of human fulfilment than other cultures; other societies have sometimes treated it as a temporary disturbance or form of mental imbalance."

Marriage is also found in all cultures often with an associated set of rituals, and always accompanied by duties and expectations for both men and women. Polygyny (when one husband has several wives) occurs in 84 per cent of cultures world-wide, but even in polygynous cultures about 90 per cent of individuals actually live in monogamous relationships. Of course, the amount of power and choice women have in relationships varies hugely around the world.

The Ache tribe of Paraguay, believe that babies inherit characteristics from all men that have had sex with the mother during the course of her pregnancy. Once the baby is born, all the "fathers" involved are expected to provide food and to help raise the child. Not surprisingly, this means that women who discover they are pregnant set out to seduce good-looking, high-status men. Sounds like fun, but unfortunately their jealous husbands are sometimes violent towards them as a result. Sexual jealousy is also a universal emotion.

The factors that attract people to one another in the first place are also constant. "All over the world people look for the same three things in a mate," says Professor Fletcher. "Personality factors related to warmth and loyalty; attractiveness and vitality; and the possession of status and resources." However, the amount of importance individuals attach to these three sets of characteristics varies. Since most of us can't manage to be kind, clever, handsome, fit and rich at the same time, people work out their own system of trade-offs and look for a partner whose desirability in the mating market is similar to their own.

Sounds fine. So where does it all go wrong? Based on more than 100 research studies that have examined thousands of marriages, two factors stand out as the best predictors of divorce; how individual partners perceive the quality of their relationship and how effectively couples resolve relationship problems. By knowing what to measure in early marriage, relationship scientists can successfully predict (to 80 per cent or better) which couples will divorce.

Contrary to popular opinion, "resolving relationship problems" doesn't necessarily mean that couples have to communicate openly and honestly. Three decades of work by, among others, John Gottman, Professor of Psychology at the University of Washington, has revealed that couples in happy and stable relationships often have quite different communication styles – some communicate obsessively à la Woody Allen and others slope off shopping or mow the lawn when problems arise. There is no evidence that one style is more effective than the other. "Honesty and mutual understanding are overrated," says Dr Baumeister. "Some studies have concluded that people who idealise each other and see each other with a dose of positive illusion have stronger, more durable relationships."

As for the differences between men and women, the "Men are from Mars" theory is half true, according to Professor Fletcher. He cites several examples of stable gender differences in intimate relationships. Women approach conflict whereas men avoid it; women attach more importance to status and resources than men in choosing mates; and men are more favourably disposed towards casual sex than women. What is not well understood however, Professor Fletcher claims, especially by pop psychologists such as John Gray, who wrote Men are from Mars Women are from Venus, is that there is a massive overlap between men's and women's responses. So about 30 per cent of men express less favourable attitudes towards casual sex than the average woman, and about 25 per cent of women are more into casual sex than the average man. Margaret Clark, a professor at Carnegie Mellon University, who is editing a Handbook of Interpersonal Processes with Professor Fletcher, also stresses the similarities between sexes: "There are far more similarities in the determinants of attraction and of successful relationships for men and women than there are differences," she says.

Dr Baumeister addresses other controversial questions about gender, sex and relationships. Whether men have a higher sex drive than women has become a political football on the psychologists' playing field, but Dr Baumeister and his colleagues have found that on every measure in every published study, men did, indeed, show a higher sex drive.

Psychological knowledge can help relationship and health professionals develop more effective therapies and counselling techniques, but whether it can help individuals directly is less certain. Psychology may not have all the answers, but it can help us to unlearn the unhelpful assumptions with which we approach relationships. There is some more good news too; Professor Fletcher stresses that knowing a lot about intimate relationships does not remove the magic or emotional power from love, or make it less likely that you will send or receive a St Valentine's Day card. Thank heavens for that.

'The New Science of Intimate Relationships' by Garth Fletcher is published by Blackwell Publishing on 14 February, £14.99.