related to an ancient way of thinking or behaving
atavistic - primitive
Something ‘atavistic’ is a throwback to a primitive or earlier way of life or doing things. Often it can be something that is innate or instinctive rather as the result of a conscious decision or a present necessity. This formal word is commonly used in reference to a feeling but it is not limited to that. Has both positive and negative connotations.
Being scared of the dark is such an atavistic fear. There’s no real sense to it, it’s just something instinctive in us.
My current project is something of an architectural atavism. The design is based on ancient Roman temples.
The politician did not win a lot of his support by making cogent arguments. Instead, he did so by appealing to the public's more atavistic impulses.