Postreproductive killer whale grandmothers improve the survival of their grandoffspring [full text – no paywall]. Stuart Nattrass, Darren P. Croft, Samuel Ellis, Michael A. Cant, Michael N. Weiss, Brianna M. Wright, Eva Stredulinsky,Thomas Doniol-Valcroze, John K. B. Ford, Kenneth C. Balcomb, and Daniel W. Franks. PNAS first published December 9, 2019. https://doi.org/10.1073/pnas.1903844116

“Why humans and some species of whales go through menopause remains an evolutionary puzzle. In humans, postreproductive females gain genetic benefits by helping family members—particularly increasing their number of surviving grandoffspring. The extent to which these grandmother benefits are important in the evolution of menopause in whales remains unclear. Here, we test the grandmother effect in resident killer whales, where females can live for decades after their last reproductive event. We show that grandmothers increase the survival of their grandoffspring, and these effects are greatest when grandmothers are no longer reproducing. These findings can help explain why killer whales have evolved the longest postreproductive life span of all nonhuman animals.”