atavistic

atavistic \at-uh-VIS-tik\, adjective:

of, pertaining to, or characterized by atavism; reverting to or suggesting the characteristics of a remote ancestor or primitive type.

Buck exhibits atavistic characteristics when his instincts and memories of an impossibly distant past "call" him and reassert themselves into his behavior.
-- Jack London, The Call of the Wild

...so that when Mrs. and Miss Hulme of Kansas City cut them dead in the Plaza one evening, it was only that Mrs. and Miss Hulme, like most people, abominated mirrors of their atavistic selves.
-- F. Scott Fitzgerald, The Beautiful and Damned

Derived from the Latin atavus meaning "ancestor," atavistic gained popularity in the 1870s.