Gruber, H. E., & Piaget, J. (1981). Darwin on man: A psychological study of scientific creativity / Howard E. Gruber. Foreword to the first ed. by Jean Piaget (2. ed.). Univ. of Chicago Press.

Gruber, Howard E., and Jean Piaget. Darwin on Man: A Psychological Study of Scientific Creativity / Howard E. Gruber. Foreword to the First Ed. by Jean Piaget. 2. ed. Chicago: Univ. of Chicago Press, 1981.

Gruber, Howard E., and Jean Piaget. Darwin on Man: A Psychological Study of Scientific Creativity / Howard E. Gruber. Foreword to the First Ed. by Jean Piaget. 2. ed. Univ. of Chicago Press, 1981.