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.
To determine, indeed, whether a rich social life had a direct fitness benefit, the researchers rated a female baboon's social lifethe proximity of neighbors and how often she engaged in groomingand 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."
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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