The Collaborative International Dictionary of English v.0.48:

atavistic \atavistic\ adj.
   1. 1 displaying characteristics of a previous cultural era or
      of a previous ancestral form; displaying atavism

   Syn: atavic, throwback(prenominal)
        [WordNet 1.5] Ataxia

WordNet (r) 3.0 (2006):

atavistic
    adj 1: characteristic of an atavist [syn: atavistic,
           throwback(a)]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "atavistic":
   aboriginal, ancestral, antepatriarchal, autochthonous, bodily,
   born, coeval, congenital, connatal, connate, connatural,
   constitutional, genetic, hereditary, humanoid, in the blood,
   inborn, inbred, incarnate, indigenous, inherited, innate,
   instinctive, instinctual, native, native to, natural, natural to,
   organic, patriarchal, physical, preadamite, preglacial,
   prehistoric, prehuman, primal, prime, primeval, primitive,
   primogenial, primoprimitive, primordial, pristine, protohistoric,
   protohuman, reactionary, recessive, recidivist, recidivous,
   regressive, retrograde, retrogressive, retrorse, retroverse,
   returnable, reversible, reversional, reversionary, revertible,
   revulsionary, temperamental