It has taken five years and cost £40,000 but a research scientist claims to have finally unravelled why it's nice to have sex.

And Dr Joel Peck has put his work to good use - producing three children at the same time as formulating his new theory.

The study, entitled 'Sex Causes Altruism. Altruism Causes Sex. Maybe', is due to be published next month.

Dr Peck, 47, who is based at the University of Sussex, argues that organisms which reproduce without having sex have no need to be nice and are inherently selfish and nasty.

They have no need to co-operate or share and, instead, fight one another for food, shelter and resources.

By mathematically laying this behavioural template over the human race, he has calculated we would wipe ourselves out in generations.

Dr Peck suggests human cloning would result in a shrinking gene pool and ultimately the annihilation of the species.

He said: "If humans became asexual it seems very likely we would quickly wipe ourselves out through sheer antagonism.

"My theory predicts that when a species becomes asexual it also becomes progressively nastier and helpful behaviour almost never occurs.

"Eventually, this sort of social degeneration can lead to the extinction of the species."

Dr Peck lives with wife Miriam, 40, a parliamentary researcher, in Stanford Road, Brighton. And while gathering evidence for the report, he was clearly taking heed of its findings.

During the past five years the couple have had three children. The youngest, Moshe, is just six weeks old.

He said: "We are doing our bit to keep co-operation going in the human species."

Dr Peck produced a mathematical model which followed the evolution of simulated sexual and asexual organisms for 10,000 generations.

The results suggested members of sexual populations were up to three times more likely to survive than their asexual rivals.

His research may solve a puzzle which has perplexed evolutionary biologists since the dawn of Darwinism - why bother having sex?

Scientists have questioned why species invest huge amounts of time and energy in locating and seducing sexual partners when they could more easily pass on their full complement of DNA by spawning their own offspring.

Dr Peck said: "For decades evolutionary biologists have wondered why sexual reproduction persists when asexual reproduction seems more efficient.

"Virtually all species that are asexual, apart from microbes, were originally sexual. But these asexual organisms are also prone to rapid extinction.

"As for sexual organisms, when the going gets tough, the nice get going - they spread out throughout the environment. These nice sorts of individuals then survive even after environmental conditions improve.

"But with asexuality niceness doesn't have a chance."

Dr Peck carried out his research at Sussex University having spent five years in the zoology department at Oxford University.

He gained his doctorate at Stanford University, part of the Ivy League elite in the United States.

His research paper will be published next month in the Proceedings of the Royal Society journal.