The life cycle is the socially defined, age-related sequence of stages individuals pass through beginning with birth and ending with death. Underlying the life cycle is the recognition that humans are biological organisms that are born, mature, and die. As with other biological organisms, reproduction is a key feature of human maturation, ensuring the persistence of the species.

Forms of the Life Cycle

In very simple societies, the life cycle may consist simply of two stages—infant and adult. Once infant survivorship is reasonably certain (typically by about age 6) young persons participate in adult work life, doing jobs that are suitable to their physical strength or as apprentices learning more complex skills. Work continues until death. But such a simple definition of the life cycle rarely endures the complexities attendant on reproduction. Among women, physical maturation separates childhood from the age when childbearing is possible. For...