First Link Made Between Social Bonds, Survival

Primatologists analyzing 16 years of observations of African baboon troops have uncovered the first concrete evidence that social relationships aid survival. Their studies support and extend studies showing that social relationships in humans and other social animals reduce stress and promote health.

The researchers, including Duke University Assistant Professor of Biology Susan Alberts, reported their findings in the Nov. 14 issue of Science. Lead author on the paper was UCLA Professor of Anthropology Joan Silk, and the other co-author was Princeton Professor of Ecology and Evolutionary Biology Jeanne Altmann. Their research was sponsored by the National Science Foundation, National Geographic Society, Louis B. Leakey Foundation, UCLA Academic Senate and Chicago Zoological Society.

"There has been this really amazing gap in our understanding of how these social systems function; because given the amount of time and energy animals invest in these social relationships, they must matter in some way. Studies on humans have shown that sociality affects physical fitness, in that it aids health," Alberts said. "But nobody has shown that it affects fitness in the Darwinian sense of helping ensure survival."

In their analysis, Silk, Alberts and Altmann specifically analyzed the relationship between sociality in female baboons, and the survival of their offspring as a measure of one component of their Darwinian fitness. The scientists chose to study females, said Alberts, because females tend to stay within the same troop, their lives are more stable than the peripatetic, rank-dependent males, and because survival of offspring is a readily observable measure of a females' fitness. The troops they studied lived in the Amboseli basin of Kenya, at the foot of Mount Kilamanjaro. The animals had been study subjects by scientists for some three decades and have become so habituated to human observers that they basically ignore them.

As data, the scientists used specific kinds of observations of social relationships that had been made on the animals since 1984. The observations consisted of some 34,000 periodic ten-minute recordings of such social behaviors as adult-adult grooming and proximity to other adult animals. The scientists correlated these data with records of survival of those females' offspring.

Their statistical analysis revealed that the social integration of the females with other adults was a significant predictor of the survival of their infants. According to Alberts, while the findings definitely show a relationship between sociality and survival, the mechanisms still remain unclear.

"There are likely a great many material and psychological benefits of social integration that contribute to survival," Alberts said. "For example, sociality with males may help survival because the male will help care for offspring. And social relationships with other females may somehow contribute to survival. Also, we know from previous studies of male baboons that social isolation produces an increase in the stress hormone cortisol. And, we know from studies of humans and captive animals that just getting groomed, getting hugs, lowers cortisol and thus lowers stress."

The researchers' findings in baboons do have broader implications for study of the value of social relationships in other animals, including humans, Alberts said.

"There's a big difference in the biological world between animals that just aggregate and those that are really social in that they invest in social relationships, even though there's a cost involved," she said. "We're in that second category and so are baboons; and our data, along with the human data on sociality and physiological health, really support the notion that natural selection favors the formation and maintenance of social bonds." Alberts added that studies of baboons could further strengthen the case that sociality in humans is fundamental to Darwinian survival.

"If we find that, in fact, baboons' social bonds bring direct benefits, that suggests pretty strongly that we humans have experienced selection to seek out social relationships because they're good for our Darwinian fitness. Such a material benefits explanation also would help explain why we experience stress when we're isolated from other humans."

To uncover such subtle benefits and their effects, the scientists are conducting both field research and studies of captive baboons. These studies, said Alberts, include both behavioral observations and analyses of hormones that will seek to correlate sociality, material benefits and physiological effects.