| Abstract: |
An unresolved question arising from human evolutionary research relates to the function of the postreproductive period in human females. If menopause is not merely an artifact resulting from the bene.ts of civilization, there must be an adaptive mechanism favoring the offspring of women who continue to thrive well past the time of their last ovulation. The grandmother hypothesis was developed on the basis of the original suggestion by Williams (1957 Evolution 11:3239) that stopping early would bene.t already-born children. This idea, combined with the concepts of kin selection (Hamilton 1964 J Theor Biol 7:152) and parental investment (Trivers 1972 Sexual Selection and the Descent of Man, Chicago: Aldine, p. 136179), was expanded to suggest that postreproductive women (in contrast to males) contribute to their inclusive .tness by extending support to their grandchildren. We used discrete time event history analysis (Allison [1984] Event History Analysis, Newbury Park: Sage
Allison [1995] Survival Analysis, Cary, NC: SAS Institute) and logistic regression on data provided in population registers (Shudmon Aratame Chod, or SAC) from a village in central Japan, covering the period from 16711871, in a preliminary investigation of the effects of household grandparental presence on the probability of a childs death. We found that after accounting for the presence of other household members, the only grandparent whose presence exerted a consistent negative effect on the likelihood of a childs death was the mothers mother. Due to the small sample size of households that contained maternal grandmothers, these results failed to achieve statistical signi.cance. Their importance, however, is in what they suggest about future research, i.e., census data from preindustrial societies can provide a basis for testing evolutionary proposals, including the grandmother hypothesis.
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