When he was a Nebraska farm boy, little Alvin Johnson studied so hard that his classmates called him "Professor Frog." He read so much that his neighbors were sure he would go "brain-broke." But to his own Danish-born parents, Alvin was something special. "This boy," proclaimed his grandfather proudly, "will be a philosopher."
Alvin Johnson never held himself out as a philosopher, but he did become a scholarwith a spectacular sort of wanderlust that eventually made him famous. A kindly, ruddy-faced man who wandered from medicine to the classics to economics, he taught at...