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Human Instinct TV Programmes

Programme 2 - Deepest Desires.

Wednesday 30 October 2002 9-10pm

The instinct to have sex is one of the most potent we possess. It’s vital if we are to produce the next generation. In this programme we find out what it is about the way we look, the way we smell and what we possess, that can attract the ideal mate.

Robert Winston and salsa partner
Salsa dancing is one way to express our deepest desires.

The Perfect Date

Our instincts drive all of us to have sex - and so potentially to have children. But the way men and women go about this is very different.

Two actors were sent on to a London University campus with hidden cameras to ask a simple question: "Will you sleep with me?" One is a woman asking men and the other a man asking women.

The results could not be more different. Just as in the original experiment (by Elaine Hatfield of the University of Hawaii and Russ Clark of the University of North Texas) no women said yes but three-quarters of the men thought it sounded a good idea.

The difference in men and women’s approach to sex has an evolutionary basis. Each month a woman releases just one egg. Should this egg be fertilised she then has to carry the baby through nine months of pregnancy.

It’s a big investment. In contrast a man has virtually limitless sperm available and could father hundreds of children in the same nine months. So it’s not surprising that women tend to be more choosy when deciding just who to have sex with.

Man and woman in bed
Men and women both want children, but they have evolved very different approaches to the mating game.

A Match Made in Heaven

When looking for a partner people instinctively respond to a whole range of signals. The simplest of these is body shape. For women, a narrow waist and wide hips are a sign of fertility and therefore prove highly attractive to men.

Women are instinctively drawn to body shapes that signal good genes. So she is more likely to go for a man with wide shoulders and a narrow waist- a sure signal of both physical strength and a good immune system.

But we also detect potential partners in more subtle ways. At Newcastle University Craig Roberts asks women to wear a T-shirt for several days. Men are then invited to choose the one they think smells best.

Almost invariably the men prefer the smell of women who have an immune system very different to their own. This makes good evolutionary sense - children born to parents with different immune systems have the best chance of fighting off illness themselves.

Ian Penton-Voak of Stirling University and David Perrett of the University of St Andrews have been asking women to pick out attractive men, with fascinating results.

If they happen to be ovulating they overwhelmingly prefer a more masculine face. Thicker necks, and broader jaws and chins - typically indicators of strength and health- all desirable genetic qualities.

Chimp eating a banana
Top banana - comparatively, chimps have the biggest testicles of all our ape relatives.

Love Rats

Because women give birth they can be sure any child they have carries their genes. Men cannot be 100% certain, so they have evolved a means of protecting against the possibility of cheating partners.

It’s all down to testicle size - a man’s are bigger than a gorilla’s, but smaller than a chimp’s. A gorilla has a harem of females dedicated to him and him only.

So he doesn’t need a whole lot of sperm at the ready. But female chimps aren’t faithful at all, so the males ejaculate as much as possible, in to as many females as possible, to give their sperm the best chance of creating a baby.

That's why chimps' testicles are huge relative to those of a gorilla. Human females aren’t very promiscuous, but neither are they entirely faithful. This explains why the size of a human male's testicles are somewhere in between a gorilla’s and chimp’s.

But even though we’re getting closer to comprehending the relentless logic of sexual attraction, we’re still a long way from understanding the science of love.

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