Wild bonobos adopt infants outside of their social group

A new study from Durham University reveals evidence that two infant bonobos may have been adopted by adult females belonging to different social groups. This is the first time that bonobos, or any type of wild apes, have been known to adopt infants who were born outside of their social group.

According to the researchers, their findings give us greater insight into the parental instincts of one of humans’ closest relatives and could help to explain the emotional reason behind why people readily adopt children who they have had no previous connection with.

Study lead author Dr. Nahoko Tokuyama of Kyoto University has spent more than ten years studying bonobos in the Democratic Republic of Congo. She said that bonobos never cease to amaze.

“Although cases of adoption were observed in non-human primates, the adoptive mother and adoptees almost exclusively belonged to the same social group,” said Dr. Tokuyama.

“This may be because adoption is very costly behavior and because non-human primates form stable groups and have a good ability to recognize other group members.

“It’s well known that groups of bonobos sometimes encounter and associate with each other, and that those belonging to different groups can interact tolerantly.”

“However, I had never imagined that bonobos could adopt infants from outside of their groups, so these cases were quite surprising.”

The experts observed four groups of wild bonobos between April 2019 and March 2020 in the Luo Scientific Reserve. The researchers identified two infants that appeared to have been adopted by female bonobos from separate social groups.

The adults, 18-year-old Marie and 52-57-year-old Chio, were seen providing maternal care to 2.6-year-old Flora and three-year-old Ruby. The adults were observed carrying, grooming, nursing,  and nesting with the young bonobos for periods longer than 12 months.

There was no aggression between members of Marie and Chio’s social groups toward the young children. Furthermore, mitochondrial DNA samples revealed that the caregivers were not maternally related to the infants.

The researchers said this caring nature is evidence of bonobos’ strong attraction to infants and high tolerance of individuals, including immature youngsters, from outside of their normal group.

“Usually in wild animals adoptive mothers are related to orphaned infants or sometimes young females will adopt orphans to improve their own care-giving behaviours, which increases the future survival chances of their own offspring,” explained study co-author Marie-Laure Poiret.

“This means that adoption in non-human animals can usually be explained by the adoptive mother’s own self-interest or pre-existing social relationships.”

“The cross-group adoption we have seen in the cases of both Chio and Ruby, and Marie and Flora, is as surprising as it is wonderful and perhaps helps us explain adoption among humans, which cannot be explained purely by the benefits received by adoptive mothers.”

“Instead it is fair to say from the examples we have seen in bonobos that adoption in humans can be explained by a selfless concern for others and an emotional desire to offer care to someone who we have no previous connection with.”

The researchers suggest that the potential adoptions may have been driven by bonobos’ altruism, strong attraction to infants, and high tolerance towards individuals outside of their own social group.

The study is published in the journal Scientific Reports.

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By Chrissy Sexton, Earth.com Staff Writer