atavism

noun3

1. •
   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. — 1904
2. •
   The recurrence or reversion to a past behaviour, method, characteristic or style after a long period of absence.
3. •
   A 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. — 1933