Male apes are natural sexual harassers

A new study has revealed the extent to which male apes use sexual intimidation to control their mates. This could extend to our most familiar primate - humans.

No one has ever witnessed a male baboon forcing a female to have sex with him.

Environment | 21.09.2016

Now a French-English research team thinks they have found the reason: raping her is simply unnecessary. The males use a much more subtle and longer-term strategy to get the amount of sex they want.

"When I was in the field and observing the baboons, I often noticed that males were directing unprovoked attacks or chases toward females [in heat]," says Alice Baniel, an evolutionary biologist at the Institute for Advanced Study in Toulouse, France, and lead author of the study.

Such attacks started weeks before females reached ovulation and were able to make babies.

Eco Africa | 18.08.2016

Repeated aggression without cause appears to put females under constant pressure, to make them compliant when the male feels it's time for sexual intercourse.

These recent findings "question the extent of sexual freedom left for females in such societies," Baniel suggests.

The study was published today in "Current Biology".

Baboon males get more sex through long-term violence

Violence pays off

The researchers investigated two wild large chacma baboon groups at Tsaobis Nature Park in Namibia over a period of four years.

They observed males chasing females around for half a minute or more, biting them, shaking them or pushing them strongly onto the ground.

A male might also chase a female up a tree and push her onto thin branches, co-author Elise Huchard of the University of Montpellier, France, tells DW.

The female gets stuck there, where the male continues to harrass her for several minutes. "And she is screaming and screaming and screaming." Sometimes the male forces her to jump from the tree, Huchard says "and when it is very high up, she might hurt herself. It is very nasty."

Male aggression is even a major source of injury for fertile females.

Yet, the researchers found that males who were more aggressive toward a certain female had a better chance to mate with her later on.

Observations ruled out that these copulations were motivated by a general preference of females for aggressive males - something which does occur in many other species.

Product of pairing: Baby baboons are much cuter than the adults

Link to humans

"Because sexual intimidation - where aggression and matings are not clustered in time - is discreet, it may easily go unnoticed," Baniel says.

This behavior is already known to occur in chimpanzee groups.

With baboons showing the same behavior, the researchers suggest sexual intimidation might be a common trait in primates living in large groups - particularly when males are typically larger than females.

That would include humans.

Huchard suggests that their recent findings "open the possibility that sexual intimidation has an evolutionary basis."

It would even explain sexual violence of men towards women.

"The forms of sexual intimidation in baboon societies are the same as in human societies," Elise Huchard says. "They are expressed in the context along stable bonds between one male and one female. That resembles a bit what happens with domestic violence in humans."

But Huchard stresses that this hypothesis would have to be confirmed in further studies. "It is too early to say."

Great apes - primates like us

Chimpanzee

All seven species of great apes share the following characteristics: no tail, a large skull with a large brain, a curved spine and an opposable or prehensile thumb. Like the chimpanzee, which is at home in central Africa and known for its often aggressive behavior.

Great apes - primates like us

Bonobo

The Bonobo, or pygmy chimpanzee, is a really peaceable ape. "Make love, not war" is its motto. Bonobos use frequent sex to ease tension in the group; they are also into French kissing and oral sex. Bonobos only live in the Democatic Republic of Congo.

Great apes - primates like us

Borneo orangutan

There are two species of orangutans: one lives on the island of Borneo, the other on Sumatra. Both live on trees, have very long arms and hand-like feet that they use for climbing. Bornean orangutans are squat, they are heavier than their cousins on Sumatra, and their fur is darker and longer.

Great apes - primates like us

Sumatra orangutan

The Sumatra orangutan's fur is more reddish than that of the Borneo orangutan, the males' cheek pads are less pronounced and often covered in white hair. Sumatra orangutans also spend less time on the ground than their Bornean cousins. Experts suspect the reason to stay aloft may be the Sumatra tiger, which also preys on orangutans.

Great apes - primates like us

Eastern gorilla

Gorillas are subdivided into two subspecies, the Eastern and the Western gorilla. The Eastern gorilla is bigger, its fur is darker, and the species is subdivided even further into the Eastern lowland and the Mountain gorilla (photo).

Great apes - primates like us

Western gorilla

The Western gorilla is also subdivided, into the Western lowland (photo) and the profoundly endangered Cross River gorilla. Almost all gorillas in zoos are Western lowland gorillas. In the wild, there are far more Western gorillas than the Eastern species. The former also live in smaller groups.

Great apes - primates like us

Human

Is there a great ape missing? Right: We, too are great apes. We humans are more closely related to chimpanzees and bonobos than the chimps are to gorillas. But we're the only great ape species that isn't threatened by extinction.

Related content