Kleidon (2009) concludes that warm climates impose important constraints on the evolution of large brains relative to body size, confirming our previous hypothesis (Schwartzman and Middendorf 2000). Here we update the case for our hypothesis and present a first approximation estimate of the cooling required for hominin brain size increase using a simple model of heat loss. We conclude that Pleistocene glacial episodes were likely sufficient to serve as prime releasers for emergence of Homo habilis and Homo erectus. In addition, we propose that atmospheric oxygen levels may been an analogous constraint on insect encephalization.
Schwartzman, David; Middendorf, George; and Armour-Chelu, Miranda, "Was climate the prime releaser for encephalization? An editorial comment" (2009). Department of Biology Faculty Publications. 75.