Original articles
More Status or More Children? Social Status, Fertility Reduction, and Long-Term Fitness

https://doi.org/10.1016/S1090-5138(99)00011-2Get rights and content

Abstract

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.

Section snippets

Catastrophic population dynamics

Classic models of logistic population growth assume that animal populations grow until they reach a stable state at or near K. To the extent that competition is a force shaping the evolutionary process, Darwin's initial formulation of the theory of evolution by natural selection assumed that populations are usually stable and at or near K. Under such conditions, individuals with the highest number of surviving offspring (i.e., the highest lifetime reproductive success) are favored by selection.

Social status and differential survival

The second element in our model posits that a strategy is available to individuals that increases the probability of survival through a crash relative to others in a population, but which is energetically costly to implement. Here we argue that in ranked and stratified human societies, social status is an important factor determining the probability of lineage survival through crashes. Such might be the case where a population is differentiated in terms of priority of access to resources or

Differential survival and fertility reduction: a simple model

Because the survivors of a population crash form the base for the next period of growth, it stands to reason that natural selection might favor individuals or lineages with some heritable capacity to survive (or have offspring that survive) infrequent crashes at a higher probability than others in a population. The third element in our model is the proposition that long-term fitness benefits in the form of increased survivorship through a demographic bottleneck crisis may outweigh or equal the

Status competition and fertility reduction

This model shows that, under plausible conditions, a strategy that increases the probability of survival through infrequent crashes could be selected for even if it entailed reduction of fertility in relation to others in the group with a lower probability of survivorship. Put another way, this model captures the specific environmental conditions under which reduced fertility could be adaptive. These conditions include the existence of demographic bottlenecks of sufficient frequency and

Conclusion

We have argued that what is often passed off as an occasional perquisite of high social status—higher probability of survival through famines and other disasters that create demographic bottlenecks—may in fact be the evolutionary raison d'être of status striving. Under these circumstances, humans might be willing to pay more for status than it appears to be worth in terms of net economic return in the short run. Some psychological aspects of behavior associated with social striving appear to

Acknowledgements

We thank Martin Daly, Jennifer Nerissa Davis, Henry Harpending, Monique Borgerhoff Mulder, Hillard Kaplan, Jane Lancaster, Fraser Neiman, Eric Smith, Troy Tucker, Eckart Voland, Margo Wilson, and Carla Wofsey for comments on earlier versions of this paper.

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