Monogamy in humans a response to infanticide threat

Monogamy in humans: evolved in response to the threat of infanticide. Picture: Ian Rutherford
Monogamy in humans: evolved in response to the threat of infanticide. Picture: Ian Rutherford
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MONOGAMY in humans evolved in response to the threat of infanticide, it has been discovered.

The threat of infants being killed by unrelated males has been revealed for the first time to be the main cause of monogamy in humans and other primates.

The study, by anthropologists from University College London, University of Manchester, University of Oxford and University of Auckland, also found that monogamous males are more likely to look after their children.

Infants are particularly at risk from unrelated males whilst they are still completely dependent on their mother’s, because they stop the mother from conceiving again. Killing the infant would allow the unrelated male to impregnate the mother sooner.

Protecting young

However, monogamy means that fathers are around to protect their young, and can share the childcare, reducing the length of time the infant is dependent and so allowing for the mother to reproduce again sooner. Crucially, this also means mothers can raise young with larger brains, who take longer to develop.

The evolutionary pathway to monogamy was uncovered using the statistical analysis of over 200 primate’s family trees. The method showed which behaviours evolved with monogamy, and which appeared first. This revealed that infanticide was the cause of monogamy, whereas shared parental care and females ranging alone were a result of monogamy.

Dr Susanne Shultz, from the University of Manchester, said: “What makes this study so exciting is that it allows us to peer back into our evolutionary past to understand the factors that were important in making us human. Once fathers decide to stick around and care for young, mothers can then change their reproductive decisions and have more, brainy offspring.”