Overview

• A peer-reviewed PNAS study analyzes more than 30 years of life-history and behavior data from 25 wild mountain gorillas in Uganda's Bwindi Impenetrable National Park.
• Seven females lived for over a decade after their last birth, with several still reproducing at around 35 years, the highest documented reproductive age in this species.
• Postreproductive years accounted for at least roughly a quarter of adult life in the sample because wild females rarely reach 50.
• The authors favor the mother hypothesis, citing ongoing maternal roles for even adult offspring and better physical condition in older females that cease reproducing.
• Grandmother effects are deemed unlikely due to frequent dispersal from natal groups, and the team notes the extended postreproductive span could also be a byproduct of increased longevity rather than an adaptation.