When a lion killed Sierra the baboon, her mother reacted in a way that one could call human-like: she looked to friends for support, say researchers who studied the animals.
The scientists found that baboons physiologically respond to bereavement in ways similar to humans, with an increase in stress hormones called glucocorticoids.
Baboons can lower their glucocorticoid levels through friendly social contact, the researchers say. The animals do this by expanding their social network after the loss of specific close companions.
“Our findings do not necessarily suggest that baboons experience grief like humans do,” said Anne Engh of the University of Pennsylvania in Philadelphia, one of the scientists.
“But they do offer evidence of the importance of social bonds amongst baboons. Like humans, baboons seem to rely on friendly relationships to help them cope with stressful situations.”
At the time of Sierra’s death, Engh said, her team of researchers considered her mother, Sylvia, to be “the queen of mean. She is a very high-ranking, 23-year-old monkey who was, at best, disdainful of females other than Sierra,” Engh explained.
“With Sierra gone, Sylvia experienced what could only really be described as depression, corresponding with an increase in her glucocorticoid levels.”
Engh works with Dorothy Cheney and Robert Seyfarth, also of the university, who have followed a troop of more than 80 free-ranging baboons in Botswana’s Okavango Delta for 14 years.
Their research explores primate social relationships and how these may have influenced the evolution of human social relationships, intelligence and language.
To study the response of stress among baboons, Engh and her colleagues examined the glucocorticoid levels and grooming behavior of females in the troop to see how closely they resemble patterns seen in humans. Grooming, a friendly behavior in which baboons clean each other’s fur, is the main way for baboons to strengthen social bonds.
The team’s findings were published in a recent paper in the Proceedings of the Royal Society of Biological Sciences, a research journal.
According to Engh, the death of a close family member clearly produced short-term stress among female baboons. They seemed to compensate for the loss by broadening and strengthening their grooming networks. As they resumed grooming, their glucocorticoid levels returned to normal.
“Without Sierra, Sylvia really had nobody else,” Engh said. Sierra had been not only her daughter but her closest grooming partner.
Sylvia’s depression was serious enough, it seems, to make her give up her customary snobbery. “So great was her need for social bonding that Sylvia began grooming with a female of a much lower status, behavior that would otherwise be beneath her,” Engh said.
Through her study, Engh tracked patterns in stress of the female baboons over time through their glucocorticoid levels. Stress levels increased most often during events when their lives, the lives of their offspring and their social rankings were at risk.
The leading cause of death among adult baboons is predation, usually from leopards and lions.
Female baboons’ stress levels increased most noticeably when a predator killed a close companion, such as a grooming partner or offspring, the scientists said: if the baboons merely witnessed another baboon die, they didn’t become as upset.
University of Pennsylvania. January 2006.
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