New Delhi, Nov. 30: A team of Indian scientists has combined principles of biology and tools of mathematics to resolve a long-standing puzzle of why monogamy reigns over adultery across human cultures despite advantages of secret affairs.

Evolutionary biologist Milind Watve and his colleagues at the Indian Institute of Science Education and Research (IISER), Pune, have suggested that the uniquely human traits of gossip, blackmail, and faithful monogamy are intertwined.

Their research, published on Tuesday in the journal BMC Evolutionary Biology, indicates that gossip — a form of social policing and a key force in the evolution of language — yields opportunities for blackmail which, in turn, push humans towards monogamy.

“The opportunities for blackmail are rare, but their payoffs can be huge,” said Watve, a professor of biology at IISER, Pune. “This incentive has helped gossip endure and thrive in human society despite the costs associated with gossiping.”

Without blackmail, he said, gossip is unlikely to have become as popular as it is, and modern humans might have been a lot more promiscuous than they are now.

The scientists combined principles of evolutionary biology and a tool of mathematics called game theory to analyse the costs and benefits associated with human mating.

Biologists believe that the exceptionally long periods of biparental care and division of labour needed in caring for human children is a major force that has contributed to the evolution and dominance of monogamy.

Marriage has evolved as a social institution, and adultery is discouraged across most human cultures, Watve said. But monogamy is still a puzzle for evolutionary biologists because “occult polygamy” — secret affairs — can bring genetic advantages.

“Males can have a few extra kids — that is a genetic advantage,” Watve said. “And females can derive better parenting from one male and better genes or additional resources from another male.” Anuja Damle, Bratati Ganguly, Anagha Kale, and Neelesh Dahanukar are other members of the IISER team.

Independent studies earlier have highlighted the role of gossiping in the evolution of language, but gossiping demands time and energy — its costs — and unless there is some benefit, biologists believe, such an act will not be stable in evolution.

The mathematical modeling by the Pune team suggests that opportunities for blackmail that emerge, albeit rarely, through gossiping compensates for its costs. And during the evolution of modern human mating systems, the IISER researchers said, social policing through gossping and opportunistic blackmailing maintained monogamy.

“This is not an attempt to justify blackmailing,” Watve said. “We have changed our justice systems now, but social policing and punishment was the justice system for a long time in human evolution. In those times, blackmailing must have played a role in shaping the human mating system,” he said.

Two scientists who were not associated with the study but are familiar with game theory appliations said the IISER scientists have used a well-established mathematical model to study evolutionary stable strategies and address the “well-known monogamy puzzle”.

This work appears to be part of efforts to “use evolutionary game theory for the study of human societies,” said R. Ramanujam, a mathematician at the Institute of Mathematical Sciences, Chennai.

“They seem to have done a competent job in setting up the game theoretic model, and the results look intriguing,” said Venkatramana Subrahmanian, a US-based computer scientist at the University of Maryland, College Park.

Recent genetic studies have shown that modern humans have been mainly monogamous, although displaying tendencies towards polygamy. A rigorously monogamous population would have an equal number of breeding females and males and the breeding sex ratio would be 1. In a population where males have more than one famale mate, the ratio would be greater than one.

Last year, a study by paediatrician Damian Lubuda and his colleagues at the University of Montreal, Canada, published in the American Journal of Human Genetics found that breeding sex ratio is 1.1 in Asia, 1.3 in Europe, and 1.4 in Africa.