atavistic

/ˌætəˈvɪstɪk/
adjective
  1. Relating to or showing a tendency to revert to something ancient or ancestral; resembling a primitive or earlier form.
    • His atavistic instincts kicked in when he heard the growl, making him freeze like his ancestors would have.
    • The tribe's atavistic rituals were passed down for thousands of years unchanged.
    • Some critics called the movie's violence atavistic, harking back to brutal ancient times.
Antonyms
What does "atavistic" mean? | whatsthatwordmean | whatsthatwordmean