The mathematics of sex and courtship

How many mathematicians does it take to explain why you shouldn't sleep with a man on your first date?

A British study published in the Journal of Theoretical Biology uses applied mathematics to show that, just like mother said, there are benefits in not rushing into sex.

It uses a branch of maths and economics known as game theory to explain a man's eagerness to get to home base, as opposed to the traditionally female when-I'm-good-and-ready approach.

The mathematical model looks at courtship as a "game" that ends when either party opts out of the relationship, or the woman agrees to sleep with the man.

The woman wins if she gets both a child and a mate who will stay around to help nurture his offspring, writes Professor Robert Seymour and Dr Peter Sozou of the University College of London, the University of Warwick and the London School of Economics and Political Science.

The man, on the other hand, wins by mating with any woman – even if he gets her pregnant and shoots through afterwards.

"(Game theory) may. . . help to explain long courtship in humans, and the folk wisdom that a woman is best advised not to sleep with a man on a first date," the authors conclude.

Seymour says long courtship helps the female gather information about the male.

"By delaying mating, the female is able to reduce the chance that she will mate with a bad male," he says.

Sozou adds that a long courtship in itself helps "screen out" the cads who are likely to love you and leave you.

"A good male is more willing to pay the cost of a long courtship in order to claim the prize of mating.

"Bad males give up at some random time if the female has not by then mated with them, but good males are more persistent."

Andrew Patterson, a Melbourne-based statistician with an interest in game theory who was not involved in the study, says men and women must adopt different "strategies" if they want to win the dating game.

"The woman is looking for breeding and nurturing while the male is just out to 'kick a goal'," he says.

"If the woman finds a man to breed with and help nurture her children, she wins the game. If the man gets to mate, he wins."

But unlike poker or chess, in the game of love there can be two winners, Patterson says, which means relationships can be a win-win situation.

He also points out a flaw in the study, saying the theory doesn't hold for women who are beyond child-bearing years.

"The model is great but it has a variable," he says.

"Obviously younger women may be ready to settle down and have kids, but does this apply to women over 50?"

Anne Hollands, the vice-president of the relationship advice and counselling service Relationships Australia, says the mathematical theory put forward by Seymour and Sozou makes sense in biological or evolutionary terms.

But she says relationships today are about more than "mating and producing children".

And she says there's no hard evidence that waiting to have sex leads to more happiness or success in love.

"I have no evidence to say you will be happier if you wait," she says.

However, Hollands says certain women, including those who are very young or emotionally vulnerable, would be advised to "consider their options" before rushing into sex with a new partner.

"There is a risk you could find yourself drawn into a different sort of relationship than you might have imagined," she says.