Baboon Study: Sociable Moms Have Healthier Young

John Roach
for National Geographic News
November 13, 2003
Female baboons that enjoy the close company of others raise more
successful offspring than do baboons who lead a more solitary
life, according to results from an ongoing, long-term research
project in Kenya.

"Social animals actually seem to spend a lot of time forming social bonds. They invest so much [effort] it's hard to imagine that [social bonds] don't matter. But no one had ever shown that they did," said Susan Alberts, a biologist at Duke University in Durham, North Carolina, and researcher behind the study.

The finding by Alberts, along with colleagues Joan Silk, an anthropologist at the University of California, Los Angeles, and Jeanne Altmann, a behavioral ecologist at Princeton University in New Jersey, is described in tomorrow's issue of the journal Science.

According to their study, the more social a female baboon is, the more likely her baby is to survive the hardships of infancy and reach the one-year-old mark, the age comparable to that of a five-year-old human. The benchmark signals that a juvenile baboon has a good chance of surviving into adulthood and breeding.

"In evolutionary terms, sociality is good for you," wrote Robin Dunbar, a behavioral ecologist at the University of Liverpool in England, in an accompanying commentary.

The researchers' finding is based on 16 years worth of data collected from observations of wild savannah baboons (Papio cynocephalus) in Kenya's Amboseli Basin, a wooded grassland in the shadow of Mount Kilimanjaro.

"To test this hypothesis, we had to begin several decades ago and design a data scheme that would gradually yield the nuggets that led to this finding. No quickie shortcuts here," said Altmann, who co-directs the Amboseli Baboon Research Project with Alberts.

Social Behavior

Observations in the Amboseli have revealed the complexities of baboon social life. Both sexes have several different mates throughout their lives. Females stay in the same baboon group forever, while males may roam from group to group.

When not foraging for food or sleeping, baboons spend social time hanging out together and picking twigs from each other's fur.

"The primary interactions are grooming—the equivalent of giving or receiving a good massage—[and] being in contact," said Altmann.

Female baboons tend to form the tightest bonds with their mothers, aunts, and sisters. The bonds between maternal or paternal sisters are particularly close. Since a male may live in several groups over the course of his life, his bonds are not always as strong. But they, too, are important, according to the researchers.

The team theorized that baboons' social web benefits females and their offspring because it provides a positive environment for raising young, shielding them from harassment and protecting them from predators and infanticidal attacks from dominant adult males new to the group.

Sociality Index

To determine, indeed, whether a rich social life had a direct fitness benefit, the researchers rated a female baboon's social life—the proximity of neighbors and how often she engaged in grooming—and compared her degree of sociality to the survival rate of her offspring.

Observations of these behaviors were grouped together and given a score on what the researchers label the "composite sociality index." A higher score reflected a more social baboon, said Silk, whose research was cosponsored by the National Geographic Society Committee for Research and Exploration.

The composite sociality index correlates to people, those who are surrounded by friends and those who are loners and stay isolated in their homes, Silk said.

While none of the baboons observed could be described as loners, there are certain baboons that are more social than others, said Alberts. "On a day-to-day basis, there are females that are more isolated, more peripheral, that spend less time grooming, and are less likely to have neighbors," she said.

The researchers took a baboon's score on the sociality index and compared it to how many of her offspring survived infancy to age one. According to their results, the higher a baboon scored on the sociality index, the greater were the chances that her infant would survive to maturity.

The result was the same when the researchers controlled for the effects of environment and where a female fit within the hierarchy of the baboon group. "Dominance and environment matter a lot for females," said Silk. "This result is another factor that matters."

Human Parallel

The results of the study are of particular interest to the researchers because it conforms to past studies that suggests social support has beneficial effects on human health and well-being.

"They match so nicely this data from humans," said Silk. "There is very good evidence in humans that being part of a social network has positive effects on health and longevity."

For example, studies show that among humans social isolation is correlated with increased risk of disease, accidents, and mental disorders. Among low-income women, those with more extensive social networks give birth to heavier, healthier children.

While further studies are required to determine if social behavior is beneficial in both humans and baboons for the same reasons, "the fact that it is true in humans and baboons suggests that social animals are social for a really good reason," said Alberts.

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