atavistic
adjective formal uk/ˌæt.əˈvɪs.tɪk/ us/ˌæt̬.əˈvɪs.tɪk/
（行为）返祖性的;原始的
happening because of a very old habit from a long time ago in human history, not because of a conscious decision or because it is necessary now
an atavistic fear of the dark 对于黑暗的原始畏惧