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Veteran British actor Sir Ben Kingsley’s latest role, it seems, is ordained by mother Nature. In marrying a Brazilian actress half his age last week, the 64-year-old Sir Ben — who played the role of Mohandas Karamchand Gandhi in the 1982 movie Gandhi — may have become part of Nature’s grand design to foster longevity in women.

If Sir Ben fathers a child with his bride Daniela Barbosa De Carneiro — like other men beyond their 50s have done with other younger women in the past — he may be helping to stretch the lifespans of future generations. At least this is what Indian-born scientist Shripad Tuljapurkar at Stanford University and his colleagues believe.

Tuljapurkar, who studied physics at the University of Pune and the Indian Institute of Technology, Bombay, before migrating to the US in the early Seventies, has been studying human longevity. Like other researchers working on evolutionary biology, he is confronted by an intriguing puzzle. Prevailing theories governing the evolution of lifespan suggest that human beings lose part of their defence against harmful genetic mutations after they reach the end of their reproductive lives.

This being the case, there should be a sharp rise in mortality among women after menopause which renders them infertile. In fact, British evolutionary biologist William Hamilton in the 1960s described this expected sharp increase in female mortality as a “wall of death”.

Yet women don’t die in large numbers after menopause.

It’s a puzzle that has vexed biologists.

Now Tuljapurkar and two colleagues at the University of California, Santa Barbara, believe that the sexual adventures of older men may play a role in longevity. In a paper recently published online in the journal Public Library of Science One, the researchers have proposed a mathematical model that links mating patterns of men older than 50 with human longevity.

They have questioned the standard practice of tracking only female life histories that began with Hamilton, arguing that this could lead to mistaken conclusions about the forces that shape human evolution. This is because men’s and women’s age patterns of fertility differ in important ways.

Culling data from hunter-gatherer groups, Tuljapurkar and others showed that male reproduction begins and ends later than women’s, and declines much more gradually.

“We’re not talking about all men or even average men — we’re saying some men had long reproductive lives, much longer than any women,” Tuljapurkar told KnowHow. “Men may marry younger women, may have several wives at the same time — at least in some societies, and may remarry after divorce or widowerhood. Also, older men may be richer in goods and reputation and thus attractive to women.”

Late male fertility derives from diverse cultural patterns of mating, including age gaps at marriage, serial monogamy — a series of long-term, exclusive sexual relationships entered into consecutively over the lifespan — and polygyny (the practice of having more than one wife), the scientists say in their paper. Universally, older males marry females younger than them by 5 to 15 years on an average. The mating age is more pronounced in societies that favour polygyny or in those where old men monopolise access to reproductive females.

Tuljapurkar and his colleagues have shown for the first time from a wide range of societies that men older than 50 years produce a significant number of children. “We show by precise argument that old-age reproduction in men means that men at ages 50 to 70 have significant evolutionary fitness. Therefore they are protected against the accumulation of bad genetic mutations that might otherwise increase their mortality rates.”

But because these genes are passed to women, the protective effect works for both sexes. “Even if women over 50 have no reproductive fitness, they benefit from the fitness of old men,” Tulkapurkar said.

“This seems to be interesting work,” said Niranjan V. Joshi at the Centre of Ecological Studies in the Indian Institute of Science, Bangalore. They have drawn attention to the fact that older males — much older than the age at which female reproduction ceases — continue to contribute genetically to the next generation to a significant extent, Joshi said.

This work explains in a rigorous, formal manner how the lifespan of women has continued to evolve although they stop reproducing around middle age, said Amitabh Joshi, an evolutionary biologist at the Jawaharlal Nehru Institute of Advanced Scientific Research, Bangalore.

“Males reproduce well into late life. So the genes that enhance lifespan are selected in males. These are passed down to subsequent generations,” said (Amitabh) Joshi. The genes which contribute to a long life are not on the sex chromosomes. So the benefits of such lifespan-enhancing genes are available to both boys and girls of succeeding generations.

Thus even if women over 50 have no reproductive fitness — and are therefore susceptible to harmful mutations — they benefit from the fitness of the older men. So, in addition to the riches and reputation, women may also be thankful to older men for their genes.