The brain and sex, love and bonding

8 July 2002

Published in The Age

“Do you know what cup it was we drank upon the high sea? That good, great draught inebriates us both. I would rather...live off roots and herbs with Iseult than, lacking her, be king of a wide kingdom.”

(From Tristan and Iseult - the first Western myth of romantic love.)


“When a boar is sexually aroused, characteristic chomping jaw movements cause the secretion from the submaxillary gland of a viscous, frothy saliva with a repugnant odour. The boar snorts and blows the saliva close to the head of the sow. If she...has ovulated recently, she will adopt an immobile mating stance, which is known as ‘standing’, and mating follows.”

(From a treatise on boar mating.)



The present neo-Darwinian revolution has given us a multitude of ideas about the things which surround sex - for example why gentlemen prefer youth, thin waists and (probably) blondes: why ladies go for height, personality and status.

But these hypotheses are to do with mating and survival strategies. Little has been known about the subtle bodily mechanics of human attraction.

This is starting to change. And it appears that the poets were right: there is literally a chemistry which facilitates the rise and fall of lust, love and marriage.

Pheromones - chemicals which travel through the air between male and female - are well-documented in plants, insects and animals. A female moth can attract a male from a mile away with pheromones. But till recently their role in human attraction was just speculation.

In 1994, Luis Monti-Blonc at the University of Utah put tiny wires into the vomeronasal organ (VNOs) of some volunteers. (The VNO is in the nose.) He then wafted odourless chemicals from the skins of the opposite sex under the volunteers’ noses. Their VNOs showed evidence of electrical stimulation - suggesting that the human VNO was designed to detect pheromones.

Dr Alan Hirsch is neurology director at Chicago’s Smell and Taste Research Foundation, North America’s largest clinic for treating smell and taste disorders. He told The Age that “our double-blind studies on aromas suggest that such things as cucumber and pumpkin pie sexually arouse women, and doughnuts and black licorice arouse men”.

And if lavender can increase penile blood flow 40 percent, what might female pheromones do?

A 1998, a double-blind study, Pheromonal influences on sociosexual behavior in men, was published in Archives of Sexual Behaviour. Thirty-eight heterosexual men wore synthesised male pheromones for an eight-week period. At the end of the study, these men reported having significantly more sex than those who wore an inactive placebo.

Other studies brought similar results.

Companies selling products over the Internet - including pig pheromones - have jumped on the pheromone bandwagon. (“Just use Date Mate 2000 like you would a cologne, and enjoy the fireworks.”) Dr Hirsch, who sometimes tests these products, believes most are rather dubious.

Whilst pheromone research is in its infancy, the brain’s own love chemicals are a little better-understood.

Semir Zeki and Andreas Bartels work at the Wellcome Department of Cognitive Neurology at University College, London. They employed functional magnetic resonance imaging (FMRI) on the brains of subjects who described themselves as “truly, deeply and madly in love”.

When the subjects were shown photos of their lover, blood flowed to quite different parts of the brain from when they were shown photos of a friend. It appears that love and friendship are neurochemically different. Professor Zeki told The Age:

“What is surprising, given how much of our behaviour and our daily life is in ‘romantic attachment affects’, is that the areas of the brain involved seem to be limited in number and small. One presumes that these areas have massive connections with other brain areas to affect our behaviour in this way. No-one really knows what brain chemistry is involved, because no-one has really studied these areas in any detail.”

Anthropologist Helen Fisher, Research Professor at New York’s Rutgers University, is willing to take a highly educated guess:

“I think we have evolved three distinctly different emotional systems for love,” she says. “One is the craving for sexual gratification - which is associated with high levels of testosterone in both men and women. There’s a direct link between the androgens [male hormones like testosterone] - and probably the estrogens [female hormones] - and the sex drive.

“The second emotional system in the brain is romantic love. And that’s a different feeling from the sex drive. Romantic love is infatuation, giddiness, euphoria, sleeplessness, loss of appetite, and ‘intrusive thinking’ - you can’t stop thinking about the person. And I think all that is associated with high levels of dopamine and norepinephrine. These are chemicals that are associated with euphoria, high energy, and loss of appetite.

“Romantic love is also probably associated with low levels of serotonin.”

Dr Fisher - who has covered the subject in her book The First Sex - acknowledges there is no hard science on this second stage. Her hypothesis derives from her study of neurology, and from looking “at the last 25 years of psychological research”.

“The third emotional system is attachment - that sense of calm and peace and security that you can feel with a long-term partner. In animals, attachment behaviours are associated with increased levels of vasopressin and oxytocin. These are very common chemicals in all mammals - the genes go back at least 70 million years.

“The sex drive evolved to get you out there looking for anything. You can feel the sex drive when you’re driving along in your car. And then romantic love evolved, I think, to make you focus your mating energy. To conserve it, so you don’t go after everybody. And finally attachment - that third chemical system - I think evolved so we could tolerate this other individual long enough to raise a single child, at least through infancy, as a team.”

Australia’s one million divorcees may take cheer from Fisher’s view that this three-part cycle may be designed by evolution to last something like four years. So does she see four years as the “natural” term for marriage?

“’Natural’ is not a good word... But humans seem to have cycles, like all other creatures. Among them, I think, is a four-year reproductive cycle. This cycle varies enormously however, depending on culture, individual circumstances, timing, and so on. So I’m not a total genetic determinist by any means.”

Could one’s three different systems be directed at three different people?

“Absolutely. That’s one of the problems - that they’re not always very well-connected. For example you can have deep attachment for one person, while you feel crazily romantic attraction to somebody else, while you feel the sex drive  towards somebody unrelated to either of those two. And this leaves us all in rather a pickle.”

There seems to be some evidence for Dr Fisher’s ideas in the real world. In India, arranged marriages fare much better than love-based ones, especially long-term - suggesting no strong nexus between Dr Fisher’s second and third stages. In the US, year four of marriage is the most common year for divorce.

Like so many aspects of neo-Darwinism, it seems our growing understanding of the brain’s love chemicals has the potential to upset many applecarts.