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The “Grandmother Hypothesis” posits that natural selection conserved longevity in females because older women increase their daughters’ reproductive fitness by helping reduce mortality among grandchildren. Although this theory has been previously discredited because that reduction appears small, we argue that collective breeding, when combined with the theory of disposable soma, suggests that the presence of older women may improve the fitness of populations through mechanisms beyond reduced child mortality. We use Swedish data, considered the most reliable pre-19th through 20th-century vital statistics, to test whether birth cohorts reaching menarcheal age exhibited lower mortality than expected from trends and other forms of autocorrelation when the population included relatively many older women. Results support our argument and suggest that the presence of older women in a population may enhance the fitness of younger women not only by reducing child mortality but also by reducing mortality attendant to depletion of the soma at or near menarche.