Long-term sexual intimidation had only ever been seen in chimps and humans, but now it has been observed in baboons as well. As a result, aggressive mating strategies might be present more widely among primates than previously thought.
Who would want to be a female baboon? Males have been shown to force abortions in pregnant female baboons to improve their chances of producing offspring. Now they have been seen employing long-term aggression against the females they want to mate with, finds a study in the journal Current Biology.
"This involves either chases or attacks, so that means either biting or being brutal to the female, such as pushing her to the ground," study author Elise Huchard of France's Institute for Advanced Study told IBTimes UK.
Although chasing doesn't always result in injury, this aggression is the main source of injury among females. Sometimes males chase females up trees, forcing them to retreat to ever more dangerous branches.
"She's going to try to get to the thinner branches, and quite often he's going to be screaming and screaming and screaming, pushing her further and further," Huchard said.
"Sometimes he will let her climb down, but sometimes he pushes her to jump. When in a very high tree, sometimes she really hurts herself when she falls down."
Although it is primarily fertile females that are bullied by the males, pregnant females are also sometimes attacked. Huchard recalls one instance they documented where a pregnant female was forced to jump from a high tree by a male. She hit the ground hard and her foetus aborted the next day.
This long-term intimidation increases a male's chance of fathering her offspring. The females tend to be discouraged from mating with others, and are more likely to accept the solicitation of the aggressive male. This is presumably because she is afraid of what would happen if she didn't, Huchard said.
A role for kind baboons?
Not all male baboons are vicious bullies. Some engage frequently in affectionate behaviour such as grooming and sharing food.
"It's extremely variable," Huchard said. "In some cases females seem very happy with their bond, and in some they're trying to escape them. The violence is not systematic – some bonds are actually peaceful."
Unpicking how these different behaviours play out in a baboon group will be the next step in this line of research.
"If some males are using sex coercion, are others using other strategies such as being affectionate? Does it depend on their social strategy, or their personality traits? Are some males being nice to some females but aggressive to others? We really want to get to the bottom of what is going on there."
The answers to these questions could help shed light on how sexual aggression evolved in humans.