born Feb. 20, 1894, Denver, Colo., U.S.
died Dec. 21, 1988, Baltimore, Md.
U.S. biologist.
He received a Ph.D. from Johns Hopkins University. He introduced the concept of the biological clock in a 1927 paper on animals' internal cycles (see biological rhythm ). He theorized that ancient peoples' discovery of fire changed their habits, resulting in brain-structure changes that increased their ability to learn and communicate. He helped discover relationships between behaviour and biochemistry governing sleep, stress, and disease onset.