Classic life-history theory predicts that menopause should
not occur because there should be no selection for survival
after the cessation of reproduction [1]. Yet, human females
routinely live 30 years after they have stopped reproducing
[2]. Only two other species—killer whales (Orcinus orca)
and short-finned pilot whales (Globicephala macrorhynchus)
[3, 4]—have comparable postreproductive lifespans.
In theory, menopause can evolve via inclusive fitness benefits
[5, 6], but the mechanisms by which postreproductive
females help their kin remain enigmatic. One hypothesis is
that postreproductive females act as repositories of ecological
knowledge and thereby buffer kin against environmental
hardships [7, 8]. We provide the first test of this hypothesis
using a unique long-term dataset on wild resident killer
whales. We show three key results. First, postreproductively
aged females lead groups during collective movement in
salmon foraging grounds. Second, leadership by postreproductively
aged females is especially prominent in difficult
years when salmon abundance is low. This finding is critical
because salmon abundance drives both mortality and
reproductive success in resident killer whales [9, 10]. Third,
females are more likely to lead their sons than they are
to lead their daughters, supporting predictions of recent
models [5] of the evolution of menopause based on kinship
dynamics. Our results show that postreproductive females
may boost the fitness of kin through the transfer of ecological
knowledge. The value gained from the wisdom of elders
can help explain why female resident killer whales and
humans continue to live long after they have stopped
reproducing.