Bonobos sit alongside chimpanzees as the two closest ape relatives to humans, and without getting into genetic profiles it’s pretty easy to see why. These remarkable animals exist in complex social groups, practicing behaviors that go beyond a basic need to eat, mate, and not get killed. New research published in the journal Scientific Reports is evidence of this, as it looked into the occurrence of wild female bonobos caring for – and sometimes even adopting – both related and unrelated baby bonobos.
These animals have ever-changing social lives, forming bonds with other bonobos which can be temporary or lasting. The most concrete of relationships, however, appears to be between females rather than female-male couplings. Previous research has shown that they will act like midwives for each other, protecting birthing mothers from unwanted male attention and even cupping the newborn’s head as it comes into the world. These matriarchal gangs appear to have evolved a few methods for keeping the males at bay, as it's also thought that their sexual swellings aren’t indicative of prime mating times (as is usually the case for flashy genitals) so the males are forced to put in the work socially if they want a shot at mating.
The females have each other’s backs beyond the production of young, however, as this new research believes to have witnessed two infants being adopted by adult females from different social groups. If true, the findings may be the first-ever reports of cross-group adoption in wild bonobos, a world-first potentially stretching to all wild apes.
Nahoko Tokuyama and colleagues made the observations while monitoring four groups of wild bonobos in the Luo Scientific Reserve in Wamba, Democratic Republic of the Congo between April 2019 and March 2020. An 18-year-old female called Marie had two young daughters of her own, but was also seen caring for Flora, who was just under three years old and born to Fula, a visitor to Marie’s social group before she took over with childcare. It’s not known if Fula is still alive.
A similar story was seen with Ruby, also around three, who was being looked after by an adult female estimated to be between 52 and 57 years old called Chio. Her own offspring had emigrated to a different social group, and while the biological mother of Ruby is unknown, analyses of both Ruby and Flora’s fecal mitochondrial DNA confirmed they weren’t related to their carers.
Flora snacking on some fruit with her adoptive mother Marie and Marie's biological offspring Margaux
Both Marie and Chio were observed being effective carers, carrying, grooming, nursing and nesting with their potentially adopted kids for upwards of a year. The other members of the two adoptive mothers’ social group showed no aggression towards Flora or Ruby, despite them being the children of outsiders.
It’s difficult to draw firm conclusions from behavioral research – and unfortunately, bonobos haven’t yet adopted human language – but the findings appear to indicate that adoption in bonobos isn’t limited to related kin. It could be that bonobos’ altruistic behavior, combined with the appeal of infants, may have facilitated the willingness to care for infants regardless of their capacity to pass on the adoptive parents’ DNA.
"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," said PhD student Marie-Laure Poiret of Durham University, UK, in a statement. "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."