atavism

at·a·vism (āt'ə-vĭz'əm)
n.

1. The reappearance of a characteristic in an organism after several generations of absence, usually caused by the chance recombination of genes.
2. An individual or a part that exhibits atavism. Also called throwback.
3. The return of a trait or recurrence of previous behavior after a period of absence.

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