They band together to protect their families from aggressive gangs. They just hope that if gangs attack, it will be their neighbor’s family and not their own. Indeed, they hardly know (much less care about) their neighbors at all.

Their interpersonal love lives and family structures are in constant flux, so that if you miss a day of watching them, you’ll lose track of who’s now pregnant, who has died, and who has stolen another’s mate.

A gated community? Suburbanites? Characters on a soap opera?

No, no, and no. These are geladas, a close primate cousin of baboons that live exclusively in the highlands of Ethiopia. With the enormous groups in which they live, their intriguing red patch of skin on their chest and neck, and their peculiar behavior patterns, geladas were an irresistible research focus for two U-M scholars: Jacinta Beehner, an assistant professor in the Anthropology and Psychology departments, and Thore Bergman, an assistant professor in Psychology and Ecology and Evolutionary Biology.  

“They are highly social. And like other primates, most of them don’t suffer too many food shortages. That gives them at least a few hours in their day to make someone’s life miserable,” Beehner says, “much like humans.”   

View the slideshow for a glimpse of geladas in the wild (story continues below). Photos: Clay Wilton.

Since 2005, Beehner and Bergman (who are married) have studied geladas in the Simien Mountains National Park with the help of numerous graduate students from U-M and other universities. One, Noah Snyder-Mackler of the University of Pennsylvania, has written several articles for the New York Times about the experience, including one headlined “Next on ‘The Gelada Bachelorette.’

“Geladas have their own version of the reality TV show ‘The Bachelorette.’ They are matrilocal, meaning that males disperse at sexual maturity and females stay put, forming the backbone of gelada society,” Snyder-Mackler wrote. “When they get tired of their dominant male, or leader, female geladas decide who gets to be the new leader. Males have no say in the matter.”

Indeed, says Beehner, “unattached” bachelor males will fight for the chance to be the leader of a group, or harem, in order to have a chance to mate with the females in the group. “There’s a gang of bachelor males. They’re hoodlums,” she says. “One will end up as the leader of the harem, and the other bachelors will move on to cause grief to some other family male.”

The researchers have made many other discoveries about the lives of the primates. For instance, they were first drawn to geladas in part because of the large group size—sometimes up to 1,000 geladas living together. But they since discovered, Beehner notes, that even though they live almost on top of one another in these huge groups, the gelada males really only know their own families. “They don’t recognize any of the other families around them—even families that they see every day,” Beehner says. “With the exception of humans, this is extremely unusual for a primate.” 

While the gelada social structure can be entertaining and lively, there also is a dark side. The research team led by Beehner and Bergman has investigated a gruesome aspect of gelada life: infanticide. The practice is common when a new male becomes the leader of a harem. He will want as many of the females as possible to sire his offspring. They can’t do so, of course, if they are pregnant with another male’s offspring or if they are nursing an infant. So the new leader male will take matters into his own hands by killing the infants to make way for his own offspring. 

But there is a brighter aspect of this trend: Many females are reacting in wily and devious ways. Some may act as if they are not pregnant when a new male moves in, and will mate with the new leader. And while geladas are smart, they can’t count. So when a baby gelada arrives, say, three months later, the new male leader has no idea that the full gestation period of six months hasn’t elapsed.

With these crafty moves, some female geladas are finding ways to protect their offspring and to fight back against the actions of a male leader. Think of it as a women’s lib movement, high up in the mountains of Ethiopia.