While at Harvard, he was interested in how animals learn (ethology), and worked with William James. Afterwards, he became interested in the animal 'man', to the study of which he then devoted his life. Edward's thesis is sometimes thought of as the essential document of modern comparative psychology. Upon graduation, Thorndike returned to his initial interest, educational psychology. In 1898 he completed his PhD at Columbia University under the supervision of James McKeen Cattell, one of the founding fathers of psychometrics.