PRINCETON (US) — The top of the social ladder may not be all it’s cracked up to be. In baboon society, alpha males have higher stress levels than those ranked below them—even in periods of stability.
The findings, published in the journal Science, may clarify the impact of social dominance on health and well-being of human and other and other animal populations.
“An important insight from our study is that the top position in some animal—and possibly human—societies has unique costs and benefits associated with it, ones that may persist both when social orders experience some major perturbations as well as when they are stable,” says lead author Laurence Gesquiere, associate research scholar, working with Jeanne Altmann, professor of ecology and evolutionary biology at Princeton University.
A higher rate of fighting and mate guarding can have long-term negative effects on alpha male baboons. (Credit: Jeanne Altmann)
“Baboons are not only genetically closely related to humans, but like humans they live in highly complex societies.”
The study involved 125 adult male members of five social groups of fully wild-living baboons in Kenya’s Amboseli Basin. Altmann’s group has collected individual life histories and behavioral data on the population for four decades.
For the new study, researchers measured levels of both a stress hormone called glucocorticoid and testosterone in fecal samples over a period of nine years.
The collected data is five to 10 times greater in duration, number of groups, and number of individual males than any data previously available for any nonhuman primate, which allowed researchers to control for important variables that might have affected stress hormones, says Gesquiere.
The large sample size and lengthy period of observation also meant the results didn’t depend on characteristics of particular individual males, but rather reflect the long-term effects of dominance rank.
“We’ve known for decades that alpha males have an advantage in reproduction, but these results show that life at the top has a real downside, and that being an alpha male comes at a real cost,” says study co-author Susan Alberts, professor of biology at Duke University.
Baboons’ heightened stress levels are most likely based on the energy they must expend to maintain their social position, rather than psychological factors. For instance, alpha males are involved in a higher rate of fighting and mate guarding than beta males.
They do not differ, however, in the rate of challenges to their status, which is considered a psychological stressor, or in the amount of grooming they receive from adult and juvenile females, which is a measure of psychological support.
“Baboons are likely to be good models to provide insights for identifying the ideal position in a complex society under different conditions,” Altmann says. “Humans also live in stratified societies, and social status is well known to be associated with some but not all health outcomes in humans.
“It has been difficult to identify many of the mechanisms behind these associations,” she adds. “Our results point to the need for research that will identify and evaluate the specific costs and benefits of various status positions, in various species, types of organizations and groups, and under different ecological conditions.”
The research was funded by the National Science Foundation, the National Institute of Aging and the National Institute of Mental Health.
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