The ratio of males to females in a population, the adult sex ratio (ASR), is already known to affect social behaviour in animals such as mating, infidelity and parenting roles. Now scientists from the Milner Centre for Evolution have been given a prestigious award from the Royal Society to investigate the impact of skewed sex ratios on human societies.

The APEX Awards, delivered jointly by the British Academy, the Royal Academy of Engineering and the Royal Society, are supported by funding from the Leverhulme Trust.

Professor Tamás Székely from the Milner Centre for Evolution at the University of Bath, has been granted an APEX Award for almost £100,000 to work on the project with Professor of Evolutionary Anthropology Ruth Mace at University College London (UCL).

Professor Székely has done extensive research into the effect of skewed sex ratios on the mating behaviour and parenting roles of birds. The new research will investigate whether skewed sex ratios have the same behavioural effects in birds and mammals, including humans.

He said: “Previous studies of birds and humans show compelling evidence that rape, violence, pair bonds and parenting relate to the ratio of males and females in a society.

“However, we still don’t understand why sex ratios are biased in some societies but not in others.

“We also want to find out whether demographic shifts in ASR induce changes in social behaviour, or whether social behaviour causes an imbalance in mortality rates of males and female which creates a skewed ASR in a population.

“Importantly, the possible major impacts of sex ratio variation on human behaviour is currently under-appreciated in studies of human societies. Our research will also advise public policy makers on the implications of too few men or women in a population: do biased adult sex ratios make human societies prone to more violence, frequent changes in sexual partners and changes in parenting behaviour?”

The researchers at Bath and UCL will undertake comprehensive evolutionary analyses of sex ratio variation and social behaviour of birds and mammals, including humans. The team will compare behaviour, ecology and life-style in both human and non-human societies, and investigate whether these variations relate to ASR.

By comparing behaviour, mortalities and maturation patterns of males and females, the APEX-funded project will assess for the first time the evolutionary relationships between these traits across a broad range of vertebrate animals.

Professor Székely added: “This is a genuinely new collaboration between an evolutionary biologist and a social anthropologist to investigate the effect of sex ratios on society and will for the first time investigate whether variations in sex ratios affect human populations in the same way as other mammals and birds.”

The APEX awards support interdisciplinary and curiosity-driven research that benefit wider society, providing funding for established independent researchers to collaborate with partners from different disciplines across the sciences, engineering, social sciences and humanities.