Author's Response: Developmental structure in brainevolution

Abstract

First, we clarify the central nature of our argument: our attempt isto apportion variation in brain size between developmentalconstraint, system-specific change, and “mosaic” change, underliningthe unexpectedly large role of developmental constraint, but makingno case for exclusivity. We consider the special cases of unusualhypertrophy of single structures in single species, regressivenervous systems, and the unusually variable cerebellum raised by thecommentators. We defend the description of the cortex (or anydevelopmentally-constrained structure) as a potential spandrel, andweigh the implications of the spandrel concept for the course ofhuman evolution. The empirical and statistical objections raised inthe commentary of Barton are discussed at length. Finally, wecatalogue and comment on the suggestions of new ways to study brainevolution, and new aspects of brain evolution to study.