One of three children, Snell was born on December 19, 1903, in Bradford, Massachusetts. By 1922, he had enrolled at Dartmouth pursuing studies in biology.

He obtained a B.S. degree in that subject in 1926 and enrolled at Harvard that same year to study genetics under the renowned biologist William Castle, who was among the first American scientists to delve into the biological laws of inheritance regarding mammals. Snell received a Ph.D. in 1930 after completing his dissertation on linkage (the means by which two or more genes on a chromosome are interrelated). That same year he became an instructor of zoology at Brown University, only to leave in 1931 to work at the University of Texas at Austin following receipt of a National Research Council Fellowship.

Snell's decision to accept the fellowship turned out to be a momentous one, as he began work for the famed geneticist Hermann Joseph Muller, whose...