atavism
/ˈætəˌvɪzəm/
noun
- The reappearance of a trait or characteristic from a distant ancestor that has been absent for several generations; a throwback.
- In the family of tall people, the short child was considered an atavism to a great-grandparent.
- The child's tailbone was longer than usual, a mild atavism from our primate ancestors.
- The scientist explained that the extra toe in the horse was an atavism, not a new mutation.