Reflections on the Role of Differentiation Processes in Forming Behavioral Phenotypes: Can These Processes Replace the Concepts of Plastic Phenotype and Reversible Plastic Phenotype?

This essay presents two lines of argument to suggest that the extension into adulthood of specific phenotypic differentiation processes, typical of early development, is fundamental to the evolution of cognition. The first of these two lines of argument is organized in three steps. The first step reviews various studies of human development, highlighting that it has slowed down throughout evolution compared to that of great apes. The second step explores the relationship between this slowed development and human cognition. The third step discusses evolutionary comparative analyses that show a correlation between the evolution of cognitive processes and developmental changes. The second line of argument examines concepts of phenotype. First, the concepts of phenotype are reviewed in correspondence to the two meanings of the word plasticity (i.e., as the ability to alternate or as the ability to shape), and it is concluded that all phenotypes -rigid, plastic, and reversible-fit the meaning of shaping. It is proposed that a phenotypical process can be seen as a continuous series of functional differentiations that occur at different times during the life of the organism and at different contextual points, both inside and outside the organism. Finally, a brief recapitulation is presented that is focused on supporting the formation of behavioral phenotypes as a sequence of differentiation processes shaping the environmental interactions from the most general to the most particular.