Final answer:
The most dramatic change in family structures in the latter half of the twentieth century is the increased incidence of single-parent families, moving away from the typical married parent structure.
Step-by-step explanation:
The most dramatic difference seen in families today, compared to the past, is the increased incidence of single-parent families. Historically, the typical U.S. family consisted of two married parents and their children. However, considerable changes have taken place in family structures. The number of single-parent families has grown markedly, which includes fathers and mothers raising their children alone, reflecting a significant evolution from traditional family arrangements. The modern family unit may also include cohabitating couples, same-sex partners, and unwed parents, further diversifying the concept of what constitutes a family. This shift in family structure is notable for contributing to changes in income distribution, as single-parent families often fall at the lower end of the income scale, while two-career high-earner couples are more likely to be at the higher end.