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Does such strategic use of valuable assets ever occur among animals? For example, do elders share in the stores accumulated by the coresident-favored offspring among bannertail kangaroo rats? And do animal children compete in some way for the right to inherit?
I have argued that postreproductive females and older males were quite prevalent in preagricultural human populations and that they probably raised the reproductive fitness of their children through leadership, knowledge, and food transfers. It is unknown, however, whether the longevity of humans can, in fact. be explained by the usefulness of older humans. The contribution of postreproductive humans to the reproductive fitness of their descendants is a necessary, but not sufficient, condition for the viability of an evolutionary explanation.
Austad (in this volume) concludes with the suggestion that if there is more field work linking transmission of assets to senescence in animals, then "a generalized theory of the ecology of resource transfer across generations may emerge." The study of the evolution of longevity together with a general study of intergenerational transfers does, indeed, appear to be a promising and fascinating area for further work.
I am grateful to Timothy Miller, Shripad Tuljapurkar, Kenneth Wachter, and two anonymous referees for comments during preparation of this chapter. Research for this paper was funded by a grant from National Institute on Aging (AG1 1761).
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