Studies of intermediate wild-cultivated plants suggested that the Indica-Japonica differentiation of cultivars of Oryza sativa L. has taken place with the domestication of wild plants. The wild progenitor, which is considered to be the Asian form of O. perennis Moench, shows no trace of differentiation into two such types as the Indica and Japonica. To elucidate the potentiality of the wild progenitor to evolve the two types when domesticated, the selfed progenies from an Indica × wild and a japonica × wild cross were examined with regard to three characters known to be useful for distinguishing between the two types. The data showed that Japonica-like plants were derived from the Indica × wild cross and Indica-like plants from the Japonica × wild cross. The Indica-Japonica differentiation was considered to have resulted from selection of incipient domesticates having such potentiality under different climatic conditions; the dynamics was discussed.