When grandmothers matter

In a recent issue of this journal, Herndon discussed the grandmother hypothesis and its implications for studies on cognitive ageing. According to this hypothesis, the long post-reproductive life span in human females is an adaptive mechanism that evolved to maximize female fitness by investing resources in the care of their grandchildren rather than by continuing to reproduce themselves. From this, Herndon deduces that special cognitive robustness to be maintained until after the age of menopause must have co-evolved because grandmothers can only exert the beneficial effect if their cognitive abilities remain intact. He therefore pleas to compare cognitive ageing in humans with other primates, especially chimpanzees, because they lack a long post-reproductive life span and would therefore not have evolved this cognitive robustness. Here, we question the important role of grandmothers in our evolutionary past, first because of the different family structures during this time and second because of the low number of females that actually lived to experience a post-reproductive lifespan. We also show that in a population that reflects our evolutionary past, grandmothers do not have an important role for child survival. Finally, we react on the implications for the study of cognitive ageing as put forward by Herndon.