ETYM Latin atavus an ancestor, from avus a grandfather.
A reappearance of an earlier characteristic; SYN. reversion, throwback.
Reversion to early or ancestral type; “throw-back”; recurrence of hereditary feature after an interval of a generation or more.
(Latin atavus “ancestor”) In genetics, the reappearance of a characteristic not apparent in the immediately preceding generations; in psychology, the manifestation of primitive forms of behavior.