Putnam later served as chief executive officer of Delta Air Lines and held a seat on its board of directors until his death.

He was also related to the physical anthropologist Carleton Coon, with whom he corresponded closely regarding theories of anatomical and biological differences between human races.

Putnam's best known work is Race and Reason: A Yankee View (1961), a book critical of desegregation which originated in a letter he wrote to Dwight Eisenhower protesting about the end of segregation[clarification needed] in U.S. public schools.

"[8] After Race and Reason: A Yankee View was made required reading for high school students in Louisiana, the American Association of Physical Anthropologists (AAPA) passed a resolution condemning it.

[10] Putnam also wrote a biographical book on Theodore Roosevelt's youth that was praised by Edmund Morris, the author of the best known biography of that president.