Sexually transmitted infections 'drove humans to monogamy'

Sexually transmitted infections (STIs) such as chlamydia, gonorrhoea and syphilis may be responsible for the development of monogamy in humans, scientists claim.

A paper published in Nature Communications, co-authored by evolutionary scientists Chris Bauch and Richard McElreath, claims the devastating impact of STIs on early human settlements led to the shunning of sexual relations with multiple partners.

Prior to the dawn of agriculture, most human communities appear to have been polygynous, where men had multiple sex partners while women only had one.

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However, the shift away from a nomadic hunter-gatherer lifestyle into settled, fixed communities, around 10,000 years ago, was paralleled by a move towards monogamy as the socially sanctioned norm.

The polygynous model produces more offspring than monogamy, so evolutionary scientists have long puzzled over why the change occurred.

Bauch and his team attempted to solve the riddle using computer modelling to demonstrate the impact of STIs on communities of different sizes.

The computer simulations suggested that the diseases became endemic in settled communities, where they could spread among a far larger group of people who before would have lived in smaller, roaming groups. Instead of naturally petering out, outbreaks of STIs were able to spread indefinitely in these larger fixed settlements, causing widespread infertility as they raged untreated.

The detrimental effect on fertility meant communities who practised monogamy and remained free of infection could outbreed polygamists. These evolutionary advantages explain the imposition of monogamy as the norm and the social shunning and punishment of people with multiple partners, the paper suggests.

"A lot of the ways we behave with others, our rules for social interaction, also have origins in some kind of natural environment," Bauch told The Guardian, acknowledging that other factors probably also had a part to play in the development of monogamous communities.

However, not everyone is convinced by the new study. Kit Opie, of University College, London, questioned the paper's premise that polygyny was the norm in hunter-gatherer societies, arguing that evidence suggested it was "very rarely" practised.