The average family structure today is different than 250 years ago. Society has shifted from pre-industrial to industrial structures. In pre-industrial, agricultural societies, the extended family and interdependent community were the norm. With industrialization, work moved to factories in cities, families became more nuclear and isolated. Functionalists theorize the nuclear family best fits industrial needs, allowing social mobility. However, critics argue functionalists overlook diversity in family forms and negative aspects of modern family life.