atavism

The reappearance of an ancestral characteristic in an organism after several generations of absence; a throwback.

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.

Hence on false premises was built up that belief in spirits or invisible beings outside ourselves, which by some curious atavism was re-emerging in modern days among the less educated strata of mankind.

The recurrence or reversion to a past behaviour, method, characteristic or style after a long period of absence.

She had lost the power to care about his faults. Strange, sweet, poisonous indifference! She was drugged. And she knew it. Would she ever wake out of her dark, warm coma? She shuddered, and hoped not. Mrs Tuke would say atavism. Atavism! The word recurred curiously.

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.

Reversion to past primitive behavior, especially violence.

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

"...he traces the roots of objectless imperialism to three sources, each an atavism. Modern imperialism, according to Schumpeter, resulted from the combined impact of a "war machine", warlike instincts, and export monopolism".