In the late 19th century, psychologists familiar with the evolutionary theory of Darwin began seeking an evolutionary description of psychological development; prominent here was the pioneering psychologist G. Stanley Hall, who attempted to correlate ages of childhood with previous ages of humanity. James Mark Baldwin, who wrote essays on topics that included "Imitation: A Chapter in the Natural History of Consciousness" and "Mental Development in the Child and the Race: Methods and Processes", was heavily involved in the theory of developmental psychology. Sigmund Freud, whose concepts were developmental, significantly affected public perceptions.