Hominin forager technology, food sharing, and diet breadth.

We propose a predator-prey model to explain diachronic changes in Palaeolithic diet breadth. The fraction of rapidly-reproducing hard-to-catch hares and birds among small animals in the hominin diet shows a significant increase between the Middle and Upper Palaeolithic in the Levant, with an associated decrease in slowly-reproducing easily-caught tortoises. Our model interprets this fraction in terms of foraging effort allocated to, and foraging efficiency for each of these two classes of resource, in addition to their abundances. We focus on evolutionary adjustments in the allocation of foraging effort. The convergence stable strategy (CSS) of foraging effort and the dietary fraction of hares/birds are both highly sensitive to variation in the foraging efficiencies, which may have been upgraded by advanced technology introduced from Africa or developed locally. A positive correlation (not necessarily a cause and effect relationship) is observed between this fraction and forager population when the foraging efficiency for hares/birds is varied. Overexploitation can however result in a reduction of both diet breadth and forager population, as can food sharing within the forager group. Food sharing is routine among recent (and perhaps also Palaeolithic) foragers. We speculate that some controversial issues regarding this public goods problem might be resolved if we could incorporate sexual selection into our model.