Why are grandparents a new idea for Jonas in te giver?

Grandparents are a new idea for Jonas in "The Giver" because he lives in a community where family units consist of only two parents and two children. The concept of extended family, including grandparents, is not present in their controlled society where children are assigned to families and raised by designated parents who are not related by blood. Therefore, the idea of grandparents as ancestors is foreign to Jonas.