Throwback (7)
I believe the answer is:
atavism
'throwback' is the definition.
(synonyms)
This is all the clue.
(Other definitions for atavism that I've seen before include "Reversion to primitive type" , "Reversion to a former type" , "Reversion to ancestral type" , "Reversion to the primitive - I am vast (anag)" , "doing things the old way" .)