An assessment of the impact of population history and risk on weaning behaviour

The weaning process varies considerably among human populations, but it is not yet understood why this is the case. With this in mind, I used data from natural fertility societies to test two evolutionary theory-based hypotheses concerning variation in the timing of key events in the weaning process. First, I evaluated the null hypothesis that this variation simply reflects population history. I then tested the hypothesis that risk of resource failure affects weaning variation. Among-population variation in weaning behaviour is not correlated with the proxy I employed for population history and is only weakly correlated with some of the proxies for risk of resource failure. Thus, my analyses refute the population history hypothesis and provide only limited support for the risk hypothesis. Together, these results suggest that among-population variation in weaning behaviour is shaped by selection but, contrary to expectations, risk of resource failure is not the primary selector.