Mortality, Fertility, and the OY Ratio in a Model Hunter-Gatherer System (2014, American Journal of Physical Anthropology)
This paper in AJPA is, as far as I know, the first formal attempt to use an agent-based model as a tool for paleodemography.  Here is the abstract:

  • An agent-based model (ABM) is used to explore how the ratio of old to young adults (the OY ratio) in a sample of dead individuals is related to aspects of mortality, fertility, and longevity experienced by the living population from which the sample was drawn. The ABM features representations of rules, behaviors, and constraints that affect person- and household-level decisions about marriage, reproduction, and infant mortality in hunter–gatherer systems. The demographic characteristics of the larger model system emerge through human-level interactions playing out in the context of “global” parameters that can be adjusted to produce a range of mortality and fertility conditions. Model data show a relationship between the OY ratios of living populations (the living OY ratio) and assemblages of dead individuals drawn from those populations (the dead OY ratio) that is consistent with that from empirically known ethnographic hunter–gatherer cases. The dead OY ratio is clearly related to the mean ages, mean adult mortality rates, and mean total fertility rates experienced by living populations in the model. Sample size exerts a strong effect on the accuracy with which the calculated dead OY ratio reflects the actual dead OY ratio of the complete assemblage. These results demonstrate that the dead OY ratio is a potentially useful metric for paleodemographic analysis of changes in mortality and mean age, and suggest that, in general, hunter–gatherer populations with higher mortality, higher fertility, and lower mean ages are characterized by lower dead OY ratios.

I became interested in the OY ratio when I read the debate about what the metric might actually be telling us about human evolution.  The appeal of the OY ratio was its simplicity: it seemed to neatly sidestep some of the issues associated with estimating the precise ages of individual fossils/skeletons.  But because the age distributions of living and dead populations can be so different, what could it really tell us?

My AJPA paper uses an ABM to understand the relationship between mortality and fertility in living populations (i.e., living model populations) and the OY ratio of assemblages of dead individuals drawn from those same populations.  It leaves aside questions about estimating ages for the fossils themselves and focuses on understanding what the OY ratio means in terms of population-level conditions.

I was happy with this paper.  It came together relatively quickly, and the results from the model were pretty clear.  The first draft I submitted used the first version of the ForagerNet3_Demography model.  One of the anonymous reviewers had issues with some of the simplifications I used in the representations of reproduction and mortality in that model.  I was well into finishing up the second version of the ForagerNet3_Demography model when I got the reviews back, however, and I was more than happy to redo the entire analysis with the updated version of the model.  The results were largely the same as the first time around.  

I was really impressed by Wiley's turnaround time on publication of the manuscript: having a paper be available for distribution and citation less than two weeks after submitting revisions is like academic crack for those of who are used to waiting months or even years to see something in print.  Bravo!  The paper (still in "Early View" as of March 2014) is available here.  I am prohibited from posting a copy of the paper, but my understanding is that I can email out individual copies.  The model code and model dataset I used for the analysis are available as supplemental material along with the paper.