who specialized in the evolution of vertebrates. He obtained his Ph.D. in 1921 from Columbia University, then taught anatomy at the Bellevue Hospital Medical College, New York, and from 1923 to 1934 he was an associate professor at the University of Chicago. In 1934 he was appointed professor of biology at Harvard University, in 1945 director of the biological laboratories, and in 1946 director of the Museum of Comparative Zoology, posts he held until his death.