Chimp Mothers with Sons More Social

Chimpanzee mothers with sons are about 25 percent more social than moms and daughters, allowing their young boys to watch and learn from adult males in action, a new study indicates.

In male-dominated societies such as those of chimpanzees, you would think that cautious moms would avoid contact with too aggressive males, for fear of physical violence or even infanticide. Yet contrary to this notion, mothers of sons choose to do the opposite.

"It is really intriguing that the sex of her infant influences the mother's behavior right from birth and that the same female is more social when she has a son than when she has a daughter," researcher Anne Pusey of Duke University said in a statement.

The findings are based on nearly four decades of observations of East African chimps from the Gombe National Park in Tanzania. Researchers focused on individual monkeys, paying special attention to how much time a mother spent with non-family members, as well as with mixed-sex and female-only groups, and the average size of a mother's party.

"Drawing from the long-term datasets, we were able to investigate patterns within the same mother, examining how she behaved with her sons versus with her daughters," added lead author Carson Murray. "These results are even more compelling than a general pattern, demonstrating that the same female behaves very differently depending on the sex of her offspring."

Mother-son relationships clearly created a different dynamic, in which these caregivers spent most of their time associating with other members of their kin. During the first six months of an infant's life, mothers with sons spend significantly more time in mixed-sex parties compared to those with daughters to look after.

And due to this exposure, at 30 to 36 months, when young chimps start to venture out on their own, male infants started interacting more with unrelated chimps, especially adult males. Their female counterparts, in contrast, were not quite as gregarious.

Mothers of males seem to know the benefit of showing their sons the ropes, allowing them to observe adult males in social situation even while still hiding behind their mother's skirts, so to speak. This gives the youngsters a start on developing the social skills they'll need to thrive in the competitive world of adults.

"Mothers obviously increase social exposure for their young male infants," Murray added. "This finding leads to a larger question about how social exposure might shape gender-typical behavior in humans as well."

The study is described further in the journal Proceedings of the National Academy of Sciences.

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