Effective Population Size and the Effects of Demography on Cultural Diversity and Technological Complexity

Abstract

A central tenet of the so-called demographic hypothesis is that larger populations ought to be associated with more diverse and complex toolkits. Recent empirical tests of this expectation have yielded mixed results, leading some to question to what extent changes in population size might explain interesting changes in the prehistoric archaeological record. Here, I employ computer simulation as a heuristic tool to address whether these mixed results reflect deficiencies in the formal models borrowed from population genetics or problems with the generalizations archaeologists have derived from them. I show that two previously published and highly influential models highlight two different effects of demography. My results illustrate how natural selection and cultural selection weaken the relationship between census population size, cultural diversity, and mean skill level, suggesting that one should not expect population size to predict the diversity or complexity of a cultural trait under all conditions. The concept of effective population size is central to understanding why the effects of population size can vary among traits that are passed by different mechanisms of cultural transmission within the same population. In light of these findings, I suggest ways to strengthen (rather than abandon) empirical tests of the demographic hypothesis.