From Wikipedia: "spent his senior year at the Choate School (now Choate Rosemary Hall) in Connecticut. He then entered Yale University, where he was a member of Skull and Bones, and served in the United States Marine Corps during World War II."
So he had a broad-based education when he began acting.
Hollywood thinking: He won acclaim for the Command Decision role on Broadway (per BBC), but the studio went with the current pretty boy, who wasn't nearly the actor Whitmore was.
One of my favorite character actors. My favorite role of his was one of his first roles in the movie Battleground.