After the war his research focused on human genetics, pioneering in what is now known as gene regulation. Although not a physician, he engaged in clinical work in human genetics. In 1943 he began teaching a course in human genetics to medical students at the University of Rochester. The first edition of Stern's pioneering textbook "The Principles of human genetics" was published in 1949. Both his teaching and his textbook were instrumental in re-founding human genetics on a non-racist basis, in contrast with pre-war German and American traditions in the subject. Stern was a signatory of the 1950 UNESCO statement "The Race Question", a statement by leading scientists in many fields that questioned the validity and scientific foundations of racism.