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Monogamy in Humans

Evolution of Monogamy in Humans was the Result of Infanticide Risk

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A new study has suggested that the prime reason that monogamy evolved in humans and primates was the threat of infants being killed by unrelated males.

The team of researchers from University College London, University of Manchester, University of Oxford and University of Auckland sought to resolve the long running debate about the origin of pair living in primates. Until now, a number of different theories have been proposed including the guarding of solitary females from rival males, paternal care (when the cost of raising offspring is high), and infanticide risk (where males can provide protection against rival males).

To test out the different hypotheses, the team gathered data across 230 primate species and plotted them on a family tree of the relationships between those species. They then used statistical methods to re-run evolution millions of times across the family tree to discover whether different behaviours evolved together across time, and if so, which behaviour evolved first. The process allowed the scientists to determine the timing of certain traits emerging.

The results clearly showed that male infanticide was the cause of the transition from polygamous mating systems to monogamous ones in primates. It also showed that co-parenting was the result of monogamy rather than a cause. In other words, males who were in a monogamous partnership were more likely to care for their offspring.

Dr Kit Opie, the lead author of the study, which was published in the journal PNAS, said:  "This is the first time that the theories for the evolution of monogamy have been systematically tested, conclusively showing that infanticide is the driver of monogamy"

Infants are vulnerable to attack from other males when they are fully dependent on their mother because females delay further conception while nursing their young. This leads to the threat from unrelated males, who can bring the next conception forward by killing the infant.

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."

By April Holloway

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