Genomic evidence for the evolution of human postmenopausal longevity
In PNAS, Flavio Schwarz et al., in the laboratories of Ajit Varki and Pascal Gagneux at the University of California, San Diego/Salk Institute Center for Academic Research and Training in Anthropogeny (CARTA), report an apparent genetic signature of past selection for persistent cognitive competence at postfertile ages in humans (1). This can seem surprising because evolutionary explanations for aging (senescence) and its varying rates across species begin with the declining force of natural selection across adulthood (2). Within this framework, the rate at which selection weakens—and so the resulting rate of decline in performance with age—depends upon adult mortality risk. The higher the likelihood of surviving to older ages, the greater the fitness benefit for allocation to somatic maintenance and repair (3). Of special importance here, the strength of selection against senescence also depends on the fitness gains possible at older ages, as illustrated by slower physiological decline with age in indeterminant growers, like fish that continue to increase in rate of egg production with ever-increasing size (2).