Bonobo mothers help their sons to have more offspring

"This is the first time we can show the impact of the mother's presence on a trait of very important shape in men, which is their fertility," said Martin Surbeck, primatologist at the Max Planck Institute for evolutionary anthropology. "We were surprised to see that mothers have such a strong and direct influence on the number of grandchildren they have."

Surbeck and his colleagues observed wild populations of bonobos in the Democratic Republic of Congo, as well as wild populations of chimpanzees in Ivory Coast, Tanzania and Uganda. They found that bonobos mothers and chimpanzees pleaded for their sons in male conflicts, but that bonobo mothers did their best to support their sons' copulation efforts. This involved protecting the mating attempts of their sons from other men and intervening in attempts to mate other men.

Bonobos mothers have also been able to use their rank in the matriarchal society of bonobos to give their sons access to popular spots within social groups in the community and help them achieve high status, as well as better mating possibilities. The authors note that these interactions were rare in chimpanzee societies and had no effect on male fertility; in chimpanzees, males occupy a dominant position on females, making the actions of chimpanzee mothers less influential than those of bonobos mothers.

It is interesting to note that bonobos mothers did not offer similar help to their daughters, and there were no reports of girls being helped to raise their offspring. "In bonobo social systems, girls separate themselves from the aboriginal community and the sons stay," says Surbeck. "And for the few girls who stay in the community, of whom we do not have many examples, we do not see them receiving much help from their mothers."

In the future, Surbeck and his team would like to better understand the benefits these behaviors bring to bonobos mothers. Currently, they think that this allows an indirect continuation of their genes. "These females have found a way to increase their reproductive success without having themselves more offspring," he said, noting that the longer life of the woman Post-reproductive human, as well as early age at which the human woman can no longer discard children, may have evolved from this indirect method of continuation of their genetic lineage.

Surbeck acknowledges that collecting life-history data after breeding females in chimpanzee and bonobos communities will require a long-term collaborative study, similar to this one. "Without the help and participation of all the field sites where the data was collected, these important interactions could have been neglected," he said. "Now, as a director of a bonobos site, I look forward to exploring this further."

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