Mothers with Sons are More Social Among Chimpanzees Than Those with Daughters

Does having a boy or a girl determine how social a mother chimp is? That may just be the case. Scientists have found that the mothers of son are 25 percent more social than the mothers of daughters, spending about two hours more per day with other chimps.

Chimpanzees have a male-dominated society. This means that rank is a constant struggle and that females with infants may face physical violence or even infanticide. While it would be easier to simply avoid groups where aggressive males are present, the mothers of sons seem to seek out interaction.

In this case, the scientists analyzed 37 years of daily observations of Easter African chimpanzees in Tanzania. That data itself largely consisted of "follows," in which a research focuses on one chimp and notes her behavior and interactions with others throughout the day.

"Drawing from long-term datasets, we were able to investigate patterns within the same mother, examining how she behaved with her sons versus with her daughters," said Carson Murray, one of the researchers, in a news release. "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."

Adult males are actually more gregarious as a whole. They form coalitions with other males to assert rank, defend their territory and hunt as a group. It's very possible that mothers of sons seek out interactions in order to give their sons a chance of better learning about how to socialize.

"Mothers obviously increase social exposure for their young male infants," said Murray. "This finding leads to a larger question about how social exposure might shape gender-typical behavior in humans as well. One of the most surprising results to me was that mothers with young females still have lower association with their relatives. As we argue in the paper, this suggests that social exposure is less critical to females in general."

The findings reveal a bit more about the interactions between chimps and show that mothers with sons are more social for the sake of their sons.

The findings are published in the journal Proceedings of the National Academy of Sciences.