Male baboons that harass and assault females are more likely to mate with them, according to a new study, adding evidence that sexual intimidation may be a common mating strategy among promiscuous mammals. The study’s authors even argue that the findings could shed light on the evolutionary origins of our own species’ behavior, although others aren’t convinced the results imply anything about people.
“I think the data and analyses in this study are first-rate,” says Susan Alberts, a biologist who studies primate behavior at Duke University in Durham, North Carolina. “[But] I also think it’s a big stretch to infer something about the origins of human male aggression towards women.”
To conduct the research, Elise Huchard, a zoologist at the National Center for Scientific Research in Montpellier, France, and colleagues examined a group of chacma baboons (Papio ursinus) living in Tsaobis Nature Park in Namibia over a 9-year period. These brownish, dog-sized primates live in troops of dozens of males and females. Females will mate with multiple males throughout the year. The male chacma are about twice the size of females and aggressively fight one another and engage in howling competitions to establish dominance. The more dominant a male is, the more likely he is both to succeed in finding a mate and to sire offspring.
Males rarely force females to mate, but after years spent observing the animals in the wild, Huchard noticed that a subtler form of sexual coercion appeared to be going on. “Males often chase and attack some females of their own group when meeting another group, and they generally target sexually receptive females on such occasions,” she says. “I spent a great deal of time studying female mate choice, and my main impression … was that females don't have much room to express any preference.”
When a study came out in 2007 showing that male chimpanzees sometimes sexually coerce females—assaulting and chasing them as a kind of violent, bullying courtship—Huchard and her colleagues wondered whether baboons behaved similarly. So they meticulously catalogued the interactions between individuals living in two troops in Tsaobis’s rocky grassland.
Males often chased, bit, struck, and scratched fertile females (easily distinguished by their bright red, swollen hindquarters), but not pregnant or lactating females. These assaults weren’t immediately followed by sex. Instead, weeks later when the females were most likely to be ovulating, they tended to mate with their attackers. If a male attacked a fertile female, he was 10%–50% more likely to mate with her than were nonaggressive males, the team reports today in Current Biology.
It wasn’t that the females preferred aggressive males in general. Instead, they gravitated to the specific males that harassed them. The authors conclude that the male baboons’ behavior amounts to sexual intimidation. Though the researchers don’t know precisely why females prefer their harassers, they speculate the females fear further injury if they refuse.
The fact that such intimidation has now been seen in both chimpanzees and baboons suggests it may be common in primates with promiscuous social structures and pronounced size differences between males and females, Huchard says. Controversially, she also argues the study suggests that sexual intimidation in humans may have an evolutionary origin as a mating strategy. “Our findings … open the possibility that human sexual intimidation has a long evolutionary history.”
But others say that baboon behavior may have no implications for humans. Alberts is skeptical of drawing any evolutionary implications from the study, because human biology and social dynamics are so different from that of baboons. “While we are all primates, the two species are very different in key things, like how much bigger males are than females in baboons and how much male-to-male competition there is.” And although sexual customs and freedoms vary widely across human societies, women by and large have more choice in who they mate with than female baboons, she notes.