In addition to his pioneering studies on prenatal development of social responses in the mallard, Gilbert Gottlieb made important theoretical contributions to the study of the evolution of behavior. This tribute to Gottlieb presents his early view that prenatal behavioral development is the product of evolution and his revision of this view in his later writings. In these he saw behavioral development as a prime mover in evolution through the development of behavioral neophenotypes. These contributions place him in the company of his mentors, Z-Y Kuo, T.C. Schneirla, and D.S. Lehrman.