Young chimpanzees don’t get to pick their social circles, but their mothers do.
Baby male chimps have more mingling opportunities than their female peers, and these early social interactions seem to influence their temperaments later in life, says a new paper by George Washington University researchers.
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| Chimpanzees Glitter and Glamour (Photo credit: Carson Murray) |
After analyzing 37 years of data on Tanzanian chimpanzees from Gombe National Park, the researchers found that mothers with sons were more social than those with daughters, particularly during early infancy. Researchers say this enables the sons to observe and absorb social behaviors such as grooming, aggression and mating.
Their results, published in late November in the Proceedings of the National Academy of Sciences, raise questions about the evolutionary history of differential social exposure and also may provide insight into how human gender roles are shaped.
“It’s been known for a long time that there are sex differences in adult chimpanzee behaviors. Males are more gregarious, they form stronger social bonds with each other and they are more physically aggressive,” said Carson Murray, an assistant professor of anthropology in GW’s Center for the Advanced Study of Human Paleobiology (CASHP), and the study’s lead author.
“We wanted to understand when and how these sex differences develop and to what extent mothers influence those differences.”
Chimpanzees, like humans, form temporary social subgroups within their larger communities throughout the day. Infant chimps are also entirely dependent on their mothers for at least five years, so social interactions are restricted to those individuals with whom the mother spends time.
In an effort to find out how mothers’ friend groups affect their children, the researchers investigated differences in maternal sub-grouping patterns based on the sex of the mothers' infants.
They hypothesized that mothers with sons would socialize with others, since male offspring would need to rely more on social skills and bonds to integrate into the adult male hierarchy. Forming strong social bonds are less important for adult females who spend most of their time caring for dependent children.
“Mothers with sons are more willing to socialize and to incur costs such as competing with others for access to food or risk receiving aggression,” said Maggie Stanton, a postdoctoral scientist at CASHP.
The data from Gombe National Park dates back all the way to Jane Goodall’s hand-written entries from the 1960s.
“There have been other studies on infant chimpanzees, but the depth of information that the Gombe data set provides allows us to ask more detailed questions than ever before,” Dr. Stanton said. “We could look within individual mothers to examine if and how their behavior changes in different circumstances, so we could compare how the same mother behaved with her sons versus with her daughters.”
The study’s authors measured maternal gregariousness based on three factors: the amount of time mothers spent with non-family members; the average size of the mother’s party and its composition; and the amount of time a mother spent in co-ed versus female-only groups. They also compared social behavior at early infancy with late infancy.
They found that mothers with sons spent an average of two hours more per day with other chimps beyond immediate family members, or 25 percent more social time than mothers with daughters.
Additionally, mothers with sons spent more time around adult males during the infant’s first six months, than those with daughters, which suggests that having the opportunity to observe adult models facilitates development of social skills important for success as an adult male.
For future studies, Dr. Stanton and her research team hope to take a look at outcomes—to find out whether males who get more social exposure as infants are more successful as adults.
The results could help us better understand how parenting might contribute to sex differences in humans, since, after all, chimpanzees are our closest living relatives. But Dr. Stanton is hesitant to make a direct link between the two species.
“It’s complicated with humans,” Dr. Stanton said. “There are definitely sex differences in human behavior, but how much of that is culturally-driven and how much is due to evolution is one of the big questions that comparative studies like this can help to answer.”
Ultimately, she said, a study such as this one can help shape better research questions, since evidence on sex-specific parenting strategies is surprisingly scarce.
“I think this shines a light on an area of research that would be interesting to explore further," she said. “How mothers may have socialized with their infants throughout human history.”