Noun: Atavism (AT-uh-viz-um)
1. A recurrence in an organism of a trait or character typical of an ancestral form and usually due to genetic recombination.
2. Recurrence of or reversion to a past style, manner, outlook, approach or activity.
3. One that manifests atavism: a throwback.
Sample sentence: An example of atavism would be the appearance of reptilian teeth in a mutant chicken.