atavism

He was a magnificent atavism, a man so purely primitive that he was of the type that came into the world before the development of the moral nature. He was not immoral, but merely unmoral.

Upon the death of Theodoric in 526, Ibidus retired from public life to compose his celebrated work (whose pure Ciceronian style is as remarkable a case of classic atavism as is the verse of Claudius Claudianus, who flourished a century before Ibidus); but he was later recalled to scenes of pomp to act as court rhetorician for Theodatus, nephew of Theodoric.

I have even read in a book of criminology that the tramp is an atavism, a throw-back to the nomadic stage of humanity.