London: The reason for women outliving men has been put down to the possibility that the cells of male bodies are not genetically programmed to last as long as those of the females.

Professor Tom Kirkwood, a leading gerontologist at the University of Newcastle, believes there is now growing evidence to suggest that men are literally more disposable than women.

Kirkwood had a 'eureka moment' while having a bath one winter's night in 1977, and he came up with the theory called 'disposable soma'.

It has become the leading scientific explanation for why we age, why we cannot live forever - and now the reason why women live longer than men.

The disposable soma theory states that, although the genes are immortal and can indeed "live forever" by being continually passed on to subsequent generations, the body or "soma" is disposable because it is designed to live only long enough to act as a vehicle for carrying genes to the next generation.

The body, just like a car, needs to be maintained continuously to keep it on the road, but as time progress, the faults and errors build up within the cells and tissues.

These faults are energetically expensive to fix and with time, they become so common that the body eventually succumbs and dies. When this occurs, depends on how much effort the body spends on fixing its mistakes.

"Could it be that women live longer because they are less disposable than men? This notion, in fact, makes excellent biological sense," the Independent quoted Kirkwood as writing.

"In humans, as in most animal species, the state of the female body is very important for the success of reproduction. The foetus needs to grow inside the mother''s womb, and the infant needs to suckle at her breast.

"So if the female animal''s body is too much weakened by damage, there is a real threat to her chances of making healthy offspring.

"The man''s reproductive role, on the other hand, is less directly dependent on his continued good health," Kirkwood stated.

Females of most species tend to live longer than males, and experiments in Professor Kirkwood''s own laboratory have shown that animals that are naturally long-lived have better maintenance and repair systems than shorter-lived species.

Studies have also found that cells taken from a female body are better at repairing damage compared with cells from a male body.

"It''s always going to be difficult to say things with absolute assurance, but I think we''ve got a very convincing explanation for why women live longer than men. I''m reasonably confident that this is the explanation," Kirkwood said.

"In females, reproductive success is so inextricably bound up with the integrity of the body and the evidence is really clear right across the life course - men have a statistically significant, higher likelihood of dying at all ages compared to women.

"It seems to be deeply engrained in the biology. Obviously differences in lifestyle may add or subtract to it, but I''m absolutely convinced that there''s an underlying biological explanation for the gender differences we see between the life expectancy of the sexes," he added.

His suggestions are being published in an article in the November issue of the magazine Scientific American.