When it comes to raising their young, chimpanzee mothers are more socially outgoing and gregarious if they are caring for a boy, as opposed to a girl, according to a new study.
In a paper published Monday in the journal PNAS, researchers concluded that chimpanzee mothers in Gombe National Park in Tanzania were far more likely to spend time with larger groups of chimps if their offspring were male, especially during their offspring's first six months.
The conclusions, which were based on documented observations between 1974 and 2011, raise questions not only about how the gender roles of chimpanzees are shaped by maternal behavior, but what it may or may not say about our own evolution, according to the study authors.
Primate mothers play a key role in the social development of their offspring, and research suggests that depriving an infant of its mother's attention can foster anxiety, inappropriate aggression and an inability to form social relationships.
In the case of chimpanzees, study authors hypothesized that a mother's own socialization with other chimpanzees would foster sex-appropriate social development, according to lead author and primate behavioral ecologist Carson Murray, of George Washington University.
"Because male offspring will need to integrate into the adult male hierarchy and rely more on social skills and bonds for success as adults, whereas females will ultimately spend more of their time alone with dependent offspring, we predicted that mothers with male offspring would be more gregarious than mothers with female offspring," wrote Murray and her colleagues.
Although the authors suggest that mothers of boy chimps might be more outgoing because they are preparing them for the complicated social life of an adult male chimpanzee, they do acknowledge other possibilities.
Some mothers might be associating with adult males during the period of early infancy in order to gain protection from aggressive males who might commit infanticide.
"Another possibility is that sex-biased differences in maternal gregariousness are driven by others," the authors wrote. "Community members may be more attracted to male infants than female infants."
The authors point out that in humans, studies have demonstrated that mothers communicate in a way that encourages risk-taking by boys and vulnerability perception by girls. They say also that researchers have shown that boys with more parent-initiated interactions have greater peer acceptance and lower levels of rejection, but that "this advantage is not true for girls."
"Given early sex differences in behavior in chimpanzees and the present role of male cooperative hunting and defense in chimpanzees and humans, the question remains as to whether differential maternal grouping patterns based on infant sex were present during human evolution and contributed to the development of sex-typical behaviors," authors concluded.