Our closest cousins among the great apes, chimpanzees and bonobos, took two completely opposite evolutionary paths when it came to getting their reproductive success back on track. Chimpanzees took the thorny path of violence and coercion to secure offspring: males who beat females the most are more likely to mate with them. Bonobos followed the silk route: males do not know when females are fertile, they lead the group in a matriarchy, and they bet on mating a lot to improve their chances of having offspring.
Sex between bonobas helps them keep males at bay
The sexist violence of chimpanzees
But there is one aspect that the biologists missed: if the selfish gene only thinks about reproducing itself at all costs, in an all-out competition between males, why do chimpanzees indulge in pampering, caring and caressing, delousing and grooming each other? What is the evolutionary sense of establishing friendships with someone who is going to take away the opportunity to procreate? Primatologist Joseph Feldblum, from the University of Michigan (USA), explains: “What you would expect is to see these social ties, or strong and friendly social relationships, only if they provide some kind of benefit to individuals. Males wouldn’t spend all this time grooming other males and giving up trying to find females or food unless they made some kind of profit. “
Feldblum publishes a study today in the scientific journal Cell in which he tests this idea with a striking result: males cultivate friendships because it works for them. Thanks to decades of data collected in the Gombe National Park (Tanzania) since the time of Jane Goodall, scientists have been able to analyze the offspring of those males that bond with other mates and those that do not. And they got two results. The first is not surprising, and it is something that was already known: the males who deal the most with the alpha male of the community gain chances to reproduce. It makes sense: in this patriarchy, the alpha controls the females and allows his friends to mate. “Turning the boss around is nothing new,” says study co-author Anne Pusey of Duke University, who has spent three decades organizing and digitizing that unique data set. And he adds: “We showed that it has always been worth it.”
“It may be that the formation of these bonds reduces the need to be aggressive so often.”
Joseph Feldblum, University of Michigan
However, the scientists found that males who spend more time with other mid-range males in the community multiply their chances of having offspring. A male chimpanzee is 50% more likely to have children if he maintains at least two strong friendships with other males. Leaving alpha aside, rank in the group hierarchy does not influence the chances of reproductive success, but rather having many friends to whom you dedicate time and attention. Strategy is not violent competition, but collaboration with your peers.
Bonobos and people
That is to say, contrary to what is understood by simplifying the evolutionary perspective, the victorious strategy is not to be the strongest or most aggressive, but also to be the one who takes care of your friends the most. Feldblum believes that more studies are needed to understand how these social ties lead to success. “It may be the potential to form aggressive alliances with mates that helps males access mating opportunities, and precisely the formation of those bonds reduces the need to be aggressive so frequently, but we still need to investigate,” he says. .
The primatologist wonders: “Is it that if your ally is close, is it more likely that you will mate with a female in heat, or that having allies around you protects you from the harassment of other males? Or is it that as your ally will support you if a conflict arises, your stress levels are lower and you can devote more energy to mating efforts? ”Asks the primatologist. It is the first time that how sociability influences the ability to reproduce in males has been studied, the researchers note, because this perspective was always applied only to females.
The researchers believe that having a clearer idea of the benefits of these social relationships in chimpanzees provides clues about the evolution of friendship in humans, as explained by Ian Gilby, lead author of the study. “Along with bonobos, chimpanzees are our closest living relatives and help us identify which characteristics of human social life are unique. This study suggests that strong bonds between males have deep evolutionary roots and provided the basis for the more complex relationships that we see in humans, “said Gilby of Arizona State University in a press release. And he adds: “This research also highlights the value of long-term studies like these, which are essential to understand the biology of a species that lives for many decades and reproduces slowly.”