It was Cole Porter who wrote ‘I get no kick from champagne/ Mere alcohol doesn’t thrill me at all/ So tell me why should it be true/ That I get a kick out of you.’ Today we know that love does resemble addiction, and a powerful one at that. When people in love are shown pictures of their loved ones, their brains activate in the same areas that are stimulated by cocaine.
From where do humans gain their capacity for falling in love? Is it something we learn at our mother’s knee, or perhaps from society – inspired by great works of art and music? Or could it possibly be unromantically written in our genes? Whether you are an orphan, deaf and unable to hear great symphonies, or blind and unable to see great works of art, it appears that romantic love is a human universal. One particularly famous study in the early nineties found notions of romantic love in all but a fraction of the 168 cultures studied.
As a human universal, then, our capacity to love is likely to involve a heritable factor that gives rise to the physical and chemical changes that take place in our brains when we fall in love. We must also carry the genetic material that will construct the circuits that enable us to fall in love in the first place. In Nature via Nurture, Matt Ridley explores our growing understanding of love as an instinct. The story starts in the early 1980s, when scientists realised that the hormones vasopressin and oxytocin were doing something rather interesting in the brains of rodents. A male rat injected with intercerebral oxytocin gets an erection (and, oddly, starts yawning). A female rat similarly injected will adopt a mating posture.
Later work showed that tinkering with the levels of these hormones in the brains of prairie voles – a kind of mouse that is unusual for its faithful marriages – could trigger pair-bonding behaviour. In the wild, mating also releases these hormones and the prairie vole will bond with whichever animal it has mated. What makes this mouse unusually faithful among rodents appears to be merely a shortish stretch of DNA.
Are men, or indeed women, like mice? In many respects, genetically, they are. These hormones are found in both species and are produced and detected in the same parts of the brain. They are also produced in both species by sex. It seems likely, then, that humans have a similar genetic basis for falling in love as the prairie vole.
If love is an instinct that all humans have, having this capability does not make it inevitable. A complicated choreography of behaviour and environmental triggers are required to reach the ultimate stage of reproduction. In fact, there are probably many stages and kinds of love, all with a genetic root and related environmental triggers. Three are well known – lust, attraction and long-term attachment – and each are likely to be governed by genes and the environment. Lust, for example, might involve a chemical called phenylethylamine, a chemical relation of the amphetamines. Certain things, though, must happen to trigger this attraction. It will probably start with eye contact with someone we find attractive and move on to verbal communication with mutual gaze, and synchronisation of head, hand and body movements.
Longer-term attraction also involves judgements about the suitability of a mate. Studies such as those looking at the advertisements in lonely-hearts columns, suggest that each of us has a kind of inner scorecard against which we rate potential mates. We want mates that are attractive, intelligent, caring, generous, humorous and, if we are female, wealthy. And we weigh up our prospective mate’s scorecard against our own. If this sounds unromantic, then consider your reaction the next time you see a young, beautiful woman walking down the road arm-in-arm with an older, unattractive man. You will probably assume that the man is wealthy, but what is wealthy is relative, and what is funny depends on how you were brought up, and what is considered beautiful depends very much on fashion. So our environment partly determines what is acceptable in a mate, and what triggers our hormones.
For further proof of the environmental impact on love, look no further than your first love. It is always said that it is like no other. Why is love so much harder a second or third time? The same hormones are involved. Experience of a broken heart seems to do much to temper our eagerness to fall in love and we are pickier. Might there be some anti-love hormone at work in the brains of the timorous? Perhaps, one day, scientists will find an explanation for what popular psychology would call emotional baggage.
Similarly, the type of romantic partner we are attracted to is modified by experience. If we have been loved by aloof partners, or raised by aloof parents, then partners desiring intimacy or closeness will seem unbearably clingy. How we desire to be loved – something that determines the strength of our long-term attachments – depends on our experience. But it is also something that seems to adapt continuously, to some extent, throughout life.
Our brains, it seems, are born with instinctive modules that are fashioned by experience. Some of these modules adapt continuously throughout life. Others will change rapidly with experience and then set like cement. Sexual preference, for example, seems to be set at birth. Human fetish, though, develops at an early age and is difficult, if not impossible, to change. A fetishist will fixate on anything from feet, to stuffed toys, balloons or leather, and these are often objects associated with early sexual experiences. This sounds uncannily similar to ducklings that imprint the idea of ‘mother’ on moving objects seen shortly after birth. Might fetish, then, be a kind of sexual imprinting?
As Matt Ridley writes, ‘welcome to the world where your genes are not puppet masters pulling the strings of your behaviour; a world where instinct is not the opposite of learning, where environmental influences are sometimes less reversible than genetic ones, and where nature is designed for nurture.’ Welcome to Nature via Nurture.
NATASHA LODER, Science and Technology Correspondent,
The Economist