Asian Scientist (Aug. 1, 2013) – The threat of infants being killed by unrelated males is the key driver of monogamy in primates, according to a new study by researchers from New Zealand and the UK.
The team also found that following the emergence of monogamy, males are more likely to care for their offspring. Where fathers care for young, not only can they protect infants from other males, but they can also share the burden of childcare.
Dr Kit Opie, lead author of the study published in the journal Proceedings of the National Academy of Sciences (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. This brings to a close the long running debate about the origin of monogamy in primates.”
While social monogamy, or pair-living, is common among birds (90% of species), it is rare for mammals to practice monogamy (less than 3% of species).
A number of competing hypotheses have been proposed to explain the evolution of monogamy among mammals. These include the need for paternal care (when cost of raising offspring is high), the need to guard solitary females from rival males, and the need to protect infants against rival males.
To uncover the evolutionary pathway, the team gathered data across 230 primate species. These were then plotted on a family tree of the relationships between those species.
Bayesian methods were used to re-run evolution millions of times across the family tree to discover whether different behaviors evolved together across time, and if so, which behavior evolved first.
This allowed the team to determine the timing of trait evolution and show that male infanticide is the cause of the switch from a multi-male mating system to monogamy in primates, while bi-parental care and solitary ranging by females are a result of monogamy, not the cause.
Infants are most vulnerable when they are fully dependent on their mother because females delay further conception while nursing slowly developing young. This leads to the threat from unrelated males, who can bring the next conception forward by killing the infant.
“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,” said Dr Susanne Shultz, a co-author of the study.
The article can be found at: Opie et al. (2013) Male Infanticide Leads To Social Monogamy In Primates.
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Source: University College London; Photo: Tambako the Jaguar/Flickr.
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