Thomas Hunt Morgan ( September 25 , 1866 - December 4 , 1945 ) was an American evolutionary biologist , geneticist and embryologist and science author who won the Nobel Prize in Physiology or Medicine in 1933 for discoveries elucidating the role the chromosome plays in heredity .
Thomas Hunt Morgan ( 25 September 1866 - 4 December 1945 ) was an American geneticist and embryologist .