Family development theory was one of the first theories developed in the late 1940s to view families as social groups that progress through defined stages of development influenced by life cycles. It proposes that families experience roles and tasks at each stage of development. The systemic family development model expanded on this by addressing its assumptions of universality and single-generation focus. It emphasizes stressors on the family and transitions rather than rigid stages, recognizing the complexity and diversity of families. The movie Coco illustrates this well by showing a multigenerational family navigating the stress of Miguel's love of music on the family system.