The chemistry between us

What is looooove?", as Howard Jones so memorably intoned. For centuries we've looked to the arts to help us out, and to explain why for "each ecstatic instant/ We must an anguish pay". And where's that got us? Divorce rates through the roof and J-Lo. So, maybe it's time to look elsewhere. Can scientists help us with love?

Dr Helen Fisher, research professor of anthropology at Rutgers University, New York, has been studying romantic love in animals - including us - for over 30 years. Her latest book is Why We Love: the Nature and Chemistry of Romantic Love; and she is examining the subject in a new four-part series on the BBC World Service. Topics include recent brain-mapping research which shows that romantic love is actually an instinct; why the brain chemistry of romantic love can trigger sexual desire; and why, in turn, sex can trigger feelings of attachment. She also takes in casual sex, polygynous sex, polyamory (loving a number of people simultaneously) and swinging. And in the first programme, she explores why, although expressions of love differ over cultures, our feelings apparently are the same everywhere.

"Falling in love is as basic to living as the fear response," Dr Fisher says. "It is exactly the same regardless of age or gender. It's a sophisticated evolutionary response."

After all, we are told all the time that falling in love is simply a chemical reaction in the brain, akin to a form of temporary insanity. To which our normal reaction is, "Well, yes, for other people, maybe. But we are completely different and nobody has ever been in love like us before." Thankfully, Dr Fisher has taken it a step further, and split the process into three handy divisions: lust, attraction and attachment.

Stage one: lust This is our sex-drive, the thing that makes us get out the house and go on the pull. A basic instinct, it's easily stimulated and relatively indiscriminate.

Last year, the University of St Andrews in Scotland conducted experiments in which volunteers rated the attractiveness of faces on a screen. Both men and women showed a preference for faces that closely resembled their own (look at Jennifer Aniston and Brad Pitt, Kate Winslet and Sam Mendes, or Peter Kay's wife Susan, who looks like his twin).

Stage two: attraction This is what we know better as romantic love, the heart-pounding, exclusive state of thinking where your entire world revolves around one person. Starting around puberty, this is the bit where we all go demented and when girls like to write boys' names over and over again in their jotters.

When we fall in love, says Dr Fisher, our brains create such dramatic surges of energy that it even shows up on scans. What happens here is that dopamine starts shooting around, lighting up your cerebral cortex and making you immediately drop all your best friends. This is evolution pushing you towards getting serious enough to have a baby; and for you both to be sure who the father of this baby is.

While it is entirely easy to fancy lots of people at one time - Alan Clark famously fancied every woman in the world, up to and including Margaret Thatcher - it's difficult, if not impossible, to be in love with two people at one time. When you're in love, one of the most important things to you becomes sexual fidelity. The idea of your partner having sex with anyone else is an agonising torment. This is where Mother Nature has played a blinder on us: she has made us emotionally monogamous when we are in stage two but not always sexually monogamous (although we expect our partners to be well behaved). Sexual monogamy is culturally based but the emotion of falling in love crosses all human barriers. Worst of all, falling out of love, or having that stage-two love cut off, is a universal part of human suffering.

It's no wonder the whole thing is so difficult; the two stages have mutually conflicting aims, one of which is "go find anyone to make a baby with"; and the other is "of all the people in the world, only you will do".

Stage three: deep attachment This is where you aren't crazy in love any more, but are settling down to raise your children. Most of us find contentment by this point, except for celebrities, of course, who are contractually required to give interviews to magazines about how they are able to stay in phase two on a constant daily dopamine high.

Obviously, they find this slightly easier than the rest of us because they don't have to wash each others' underpants. However, it can get a little worrying when Jennifer Aniston keeps going on about how she loves Brad Pitt just as much as the day she met him.

Well, according to well-researched science, she doesn't. Nobody does. Thirty months is the outer limits of stage-two love, without which you'd end up in an asylum

Celebrities also see no problem in running around the stages as often and as quickly as possible, à la J-Lo, showing just how far away from standard cultural behaviours they're permitted to deviate.

The attachment phase is designed to last, ideally, up until the child is a teenager (of course, up until the First World War, the women would usually just die politely in childbirth anyway). These days we expect it to last for 60 years, while being surrounded by pretty bad role models for happiness all across the world.

But will knowing all this help us get it right? "Well, find the right person in the first place," says Dr Fisher. "Try to wait until the crazy stage-two stuff wears off - you couldn't live like that all the time anyway, you'd die of sexual exhaustion. And you can't see somebody's faults at that point. You're like, 'Well, he's never had a job, but I'm sure it'll be fine.' Wait until you've reached the attachment stage, where you can weave your lives together. Then, you've almost got to fool the brain. Remember our dopamine levels surge with novelty."

So, instead of just haring off at this point and finding someone new (or, if you're Rod Stewart or Boris Becker, someone exactly the same), "try new and exciting things all the time. Stimulate the brain with things you do together. Keep up the remembered romance of stage two, and that will keep the brain circuits lighting up."

Does wrenching love from the hands of the poets to the neuroscientists and anthropologists make us feel any better? Knowing that our feelings are as universal as going to the toilet doesn't change their intensity, especially when love no longer even separates us from the beasts.

"Spending 30 years studying why we love hasn't changed my feelings about love at all," says Dr Fisher. "In fact, knowing how it works expands my wonder in it - to know how people, and animals, feel all over the world and what's in store for every person in the world, today, tomorrow, a million years ago. It's a basic brain- system response, equally valid at six or 60.

"You can know every ingredient of chocolate cake and it can still bring you enormous pleasure. You can know every note of a Beethoven symphony, and it still never takes away from the passion and the fascination. In fact, if anything, this understanding just gives me even more respect for the evolutionary process."

'Love' starts on Wednesday at 9.05am on BBC World Service. 'Why We Love: the Nature and Chemistry of Romantic Love', by Henry Fisher and Helen Fisher, is published by Henry Holt, priced £14