Clark Barrett
Anthropology, UCLA
Modularity can be thought of as an architectural feature of developed phenotypes, i.e.,
an outcome of development. Two issues are often conflated: how modularity evolves,
and how modularity develops. While these are of course related, they are related in
only a very specific way: the same way that evolution is related to the development of
any phenotypic structure. One way they are not related is in the way that a blueprint is
related to a building (where evolution makes the blueprint and development makes the
building). Modules cannot be genetically specified in toto, just as any aspect of the
phenotype cannot be. Moreover, just as for other modular aspects of the phenotype
(e.g., muscle fibers, hairs, ocular dominance columns), there may be many
phenotypically distinct modules that are not constructed by distinct sets of gene loci.
Therefore, critiques of modularity that are based on attacking the "blueprint" idea
carry no weight. Rather, what evolves are genetic and extragenetic systems of
inheritance that are designed to [build, grow, generate] phenotypes in developmental
time, in concert with internal and external environments. Modular features of the
mind are in this sense generated, or grown. Often, this insight is used as an argument
against evolved modularity, as if evolution and development were somehow opposed
(e.g., Karmiloff-Smith). Instead, this paper examines the proposal that evolution
shapes the mechanisms that generate modularity to extract new insights about what
mental modularity might be like, and to address issues in the modularity debate.