Where do you stand in the social pecking order at work, your community and in your love life, and do hormones play a role? Perhaps more importantly, do you know where those around you fit in?
U-M psychology researchers are finding clues to the origins of these abilities in the wilds of Ethiopia. Researchers Jacinta Beehner and Thore Bergman have spent more than a decade studying the social skills of nonhuman primates — focusing their attention on behavioral stress, aggression, social status and mate choice.
Like humans, the vast majority of nonhuman primates cluster together in large, often complex communities and quickly establish their own pecking order.
“Of course, your own social status is contingent on who else is there with you. Rank is always relative,” says Beehner, assistant professor of psychology and anthropology at LSA. “We know primates know their own rank. The question is whether they are aware of the relative ranks of everyone else around them. We now know that some monkeys, like baboons, actually do know these things. But more recently, we are finding that as the group gets bigger and bigger, this might become more difficult to keep track of.”
Alternatively, maybe monkeys are more like suburban Americans — with a great deal of personal information about their own families, but with next to no information about their neighbors. In such cases, animals may be forced to make judgments based on status symbols. Beehner and Bergman, assistant professor of psychology, ecology and evolutionary biology at LSA, are finding that this suburban scenario seems to describe their current study subjects, the geladas of Ethiopia.
For years, Beehner and Bergman studied baboons, which live in communities of about 80-100 animals. Aided by a $300,000 National Science Foundation grant, they’ve now begun studying a close relative of baboons — the gelada — a monkey that lives only in the highlands of Ethiopia. Unlike their baboon relatives, geladas live in massive herds that can number up to 1,200 individuals — perhaps one of the largest groups of nonhuman primates.
“In these enormous groups, dominance rank is no longer the ‘currency’ by which males assess each other,” Beehner says. “We think that a male might be able to size up his rivals simply by looking at the color of his chest.”
Unique among primates, gelada males have a patch of bare skin on their chest that changes in color according to status. And Beehner believes this relationship (between color and status) might be linked by testosterone; as testosterone levels rise, male chests change from pale pink to bright red. Simply put, this chest patch could be a signal to other males to decide whether or not they want to pick a fight with a high-testosterone rival.
A remarkable feature in gelada society is that females are in charge. The gelada families are harem-based, with one male and anywhere from two to 12 closely related females comprising each family, and dozens of these families comprising the entire herd. Even though males are almost twice the size of females, if the females are not happy with their male they can evict him for a better one.
“If he’s not grooming them enough or if he’s not attentive enough, they can kick him out,” Bergman says.
And there are scores of single bachelor males wandering around, constantly on the lookout for weak or unpopular leaders. Upon spotting one, a bachelor male will pounce, in hopes of gaining the harem for himself.
“During these fights, we’ve seen the females take sides — they literally line up behind the male they like better,” Beehner says.
So, which male do the females choose? Beehner and Bergman think this depends on many different factors, one of which might be the redness of his chest. But another possibility is the sound of his voice. With bachelor males breathing down his neck, a leader male will run around in a brief display.
The final act of this dramatic display is to climb to the highest spot around and give a loud ritualized call: “eee-yow.” Bergman has been recording these calls for more than two years and has found that the quality of the call seems to coincide with the quality of the male. Just as human voices reveal strength or weakness, a bachelor might use this call to decide whether his opponent is all talk and no action.
