When chimpanzees lose their mothers, their older siblings frequently take on the role of adoptive parents, according to a new study in the journal PLOS ONE. Thanks to a nurturing brother or sister, young orphaned chimps are much more likely to survive into adulthood.
Primatologists have been monitoring the Sonso group of chimpanzees in the Budongo Forest Reserve in Uganda since the early 1990s, keeping note of deaths and adoptions. Over a 21-year span, 11 chimps became orphans after losing their mothers (female chimpanzees are the primary nurturers -- male chimps don't usually tend to their offspring). Four orphans weren't adopted, and only one, a ten year-old male, was old enough to survive without the additional care.
The remaining seven orphans lived on thanks to the adoptive care of other chimps. Only one chimp was cared for by another adult, however. The other six -- like the Baudelaire children in the Lemony Snicket stories, the scientists write -- were taken in by maternal brothers and sisters. At 9 to 11 years old (around the ages of chimp puberty), these caregiving siblings weren't old enough to be considered adult chimpanzees, but they nevertheless fulfilled motherly roles, grooming, feeding and protecting their younger kin.