Washington (AFP)

Bonobos, our altruistic, peaceful and lascivious primate cousins, live in female-dominated societies, in contrast to the more aggressive and patriarchal chimpanzees.

What we did not know, until now, is the very important role played by bonobos mothers in the sexual life of their sons: they use their social rank to ensure that their male children meet more females in phase ovulation, and prevent males from competing with them.

The behavior of bonobos mums is described in a study published in the journal Current Biology on Monday, which found that males whose mother lives in the same group are three times more likely to have offspring than males whose mother does not belong to the group.

"This is the first time that we can show the impact of the presence of the mother on a very important selective value in males: their fertility," says Martin Surbeck, primatologist at the Max Planck Institute for Evolutionary Anthropology.

"We were surprised to observe that mothers had such a strong and direct influence on the number of grandchildren they have," he adds.

For their study, the researchers followed groups of bonobos from the Democratic Republic of Congo, as well as chimpanzees from Côte d'Ivoire, Tanzania and Uganda - the two species of primates closest to humans, with whom they share 99% of their genetic heritage.

In both species, mothers try to help their sons, but bonobos do much better because in these communities, the highest ranks are occupied by females.

"Bonobo mums act like social passports," Martin Surbeck told AFP. "The sons, when they are in the entourage of their mother, occupy a central place in the group and access positions that allow them to further interact with other females, including copulating."

"If there is a very attractive female, we see mothers coming close, and in their shadow there are males," he says.

Conversely, when a mother loses her high status, her son also descends on the social ladder and is less likely to mate.

Girls do not seem to receive any kind of maternal assistance. Martin Surbeck's hypothesis is that mothers do not find it interesting from an evolutionary point of view, because bonobos girls end up leaving the community, unlike males.

The study confirms, according to its authors, the so-called grandmothers hypothesis: that is, a female who is no longer old enough to reproduce can increase her longevity and continue to transmit her genes, thanks to his offspring.

? 2019 AFP