Answer:
Historically, nuclear family arrangements has been the norm.
Explanation:
Social change and stability of family arrangements has been the interest of sociologist from pre-historic times. The common nuclear two-parents households common in the United States has been influenced by social change and high rates of divorce, remarriage and cohabitation. In the early 1960's, having kids was solely within the confines of marriage, but now divorce, cohabitation and influence of social change has given rise to single parenting.
