More status or more children? Social status, fertility reduction, and long-term fitness

A model is presented that shows that reduced fertility in humans can be explained as part of an evolved strategy to maximize long-term fitness in the face of periodic calamities that result in demographic crashes. Three conditions must be met for this model to be plausible: (1) human population history has been characterized by local periods of growth punctuated by recurrent crashes caused by calamities such as climatically induced resource shortfalls; (2) a strategy is available to individuals that increases the probability of survival through a crash, but that, to implement, requires diverting resources away from producing more offspring; and (3) long-term fitness benefits to increased survivorship through a crisis must outweigh or equal the fitness benefits that would accrue to putting the same resources into higher fertility, We present a model that shows that increases in survivorship can outweigh the benefits of higher fertility even if crises are neither very frequent nor particularly severe. (C) 1999 Elsevier Science Inc.