Part 5/11:
Historically, families needed multiple children to ensure that some would survive to adulthood, particularly during times with high infant mortality rates. Today, nearly all children survive into adulthood, leading families to reassess their reproduction needs. As of now, the critical fertility rate, or "replacement level fertility," which is approximately 2.1 children per woman, is projected to fall below that mark by 2050, and even lower by the end of the century.