I decided to formally wade into the cloudy waters of the Middle Paleolithic at this year's SAA meetings with a presentation titled Marriage, Mortality, and Middle Paleolithic Families: Implications of a Model-based Analysis (the abstract is here). I'm using an agent-based model (ABM) to probe how the harsh adult mortality regimes suggested for the Middle Paleolithic might have affected the behavioral conditions under which human populations were demographically viable. The model I'm using is the same as the one used in the AJPA paper with the addition of an age-specific mortality schedule that more-or-less mimics that suggested by fossil assemblages from Atapuerca and Krapina. If you're interested in the nitty-gritty of the model, full code and description are available at openABM.org.
I became interested in the OY ratio (the ratio of older to younger adults) after reading Caspari and Lee's (2004) paper and the debate that followed. While my results in the AJPA paper showed that there were clear relationships between the demographic characteristics of living populations (in the model) and the OY ratio of assemblages of dead individuals from those populations, thousands of model runs under widely varying conditions of fertility and mortality did not produce OY ratios nearly as low as those reported by Caspari and Lee for pre-Upper Paleolithic samples. But the representations and parameters in the ABM were based on data from ethnographic hunter-gatherers. What happens if we impose a mortality regime like that suggested by Atapuerca and Krapina?
Under a regime of high mortality (mortality schedule 3; MS 3 in the figures - the dotted lines are following José Maria Bermúdez de Castro & María
Elena Nicolás' 1997 paper), model populations are still "viable" if fertility is high enough. And lower OY ratios (i.e., in the Neandertal range) are associated with higher fertility populations. All things being equal, however, significantly larger population sizes are required for viability when we impose a harsh mortality regime. This makes logical sense, of course, but it also seems possibly at odds with some of the peculiarities of the Neandertal fossil/archaeological record. So I'm using the model to investigate the effects of behavioral differences (in terms of pair-bonding behaviors, "family"-like organization, etc.) on demographic viability.
I'm still working my way through the model data. I hope to be done with the presentation early (wouldn't that be a novel idea) so I can put it up here before the meetings, but I'm not sure I'll get there. The presentation will be in the afternoon session on Paleolithic Europe on 4/26/2014.
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