At″a‐vism (�), n. [L. atavus an ancestor, fr. avus a grandfather.] (a) The recurrence, or a tendency to a recurrence, of the original type of a species in the progeny of its varieties; resemblance to remote rather than to near ancestors; reversion to the original form. (b) (Biol.) The recurrence of any peculiarity or disease of an ancestor in a subsequent generation, after an intermission for a generation or two.
Now and then there occur cases of what physiologists call atavism, or reversion to an ancestral type of character.
J. Fiske