Modeling Social Status and Fertility Decisions Under Differential Mortality

Abstract

Unlike most non-human social animals, the social status of humans does not consistently correlate with higher fertility and in many cases appears to suppress fertility. This discrepancy has been employed as an argument against the use of evolutionary biology to understand human behavior. However, some literature suggests that social status and its implications for survival during high-mortality events may imply that status-seeking at a cost to fertility may be an optimal strategy over the long term. Here, we propose a theoretical model, in which each generation trades-off between social status and fertility under different economic and environmental constraints. To our knowledge, the model we present here is the first to connect individual decisions of generations, strategies to maximize long-term biological fitness, and key environmental and economic conditions in a coherent stylized modeling framework. We use it, in particular, to explicate the conditions, under which the strategy of having a lower number of offspring with higher social status may result in higher biological fitness over the long term. Furthermore, we delineate sets of economic and environmental conditions, for which the dynasty shrinks and grows. As adaptation of individual preferences is costly, limited and may take generations, we argue that a sudden change in environmental or economic conditions may shift a dynasty from a growing to a declining trajectory, which may be irreversible. Also, we show that in some cases, a slight change in environmental conditions can lead to a regime switch of an optimal strategy maximizing biological fitness.