Column-multiplication Hypothesis on Primate Neocortex Evolution

Abstract

Recently, we proposed a hypothesis that the primate neocortex may have evolved by means of the multiplication of cortical columns (column-multiplication hypothesis, Sawaguchi & Kubota, 1986). The aim of the present paper is to introduce our hypothesis to Japanese readers. The hypothesis is based on following findings; (1) the primate neocortical areas consist of anatomical and functional units of columns which are similar in size across several primate species, and; (2) the primate neocortex expansion is characterized by the multiplication of the cortical areas. In the hypothesis, evolutional mechanisms of advanced changes of the primate neocortex are explained by an analogy of “gene duplication theory” of genetics (Ohno, 1970). Further, the hypothesis predicts the existence of columns neutral for natural selection, genetic control upon the columns, intraspecies variation of the columns, and redundant structures and functions of the neocortex. Thus, the primate neocortex may have aquired not only adaptive functions, but also neutral functions, based on the columm-multiplications.