University of Zurich, Anthropological Institute and Museum
Thursday 4:00-4:15, Broadway III/IV
Encephalization of early Homo has been proposed to be related to increasing seasonal conditions of its habitat. However, in primates, no evidence for a relationship between climatic seasonality and brain size evolution has been found. We argue that it is essential to distinguish between energetic costs and cognitive benefits of relatively larger brains, and consider them both. Using monthly dietary intake of 78 primate species, we show that the energetic constraints of periodic resource scarcity, inflicted by habitat seasonality, always correlate with relative brain size. Those species that suffer from periodic resource scarcity have relatively smaller brains. However, these energetic constraints can be counterbalanced by cognitively buffering the seasonality environment in some species. Those species that can keep their intake constant despite drastic variations in resource availability have relatively larger brains. However, not all conditions are equally favorable to evolve cognitive buffering. We found that a moderate degree of habitat seasonality needs to be present, and some amount of frugi- or insectivory, to allow for leveling of dietary intake through cognitive means.
Overall, this study shows the importance of incorporating both costs and benefit perspectives simultaneously in models on brain size evolution. The evolution of early Homo in Africa is an example of how cognitive buffering can surmount energetic constraints. On the other hand, extreme periods of food scarcity may preclude the onset of cognitive buffering, e.g. in restricted island habitats like the one inhabited by Homo floresiensis.