Play emerges in the earliest mammals, likely as simple physical activities such as chasing, pouncing, or mock fighting. These behaviors help develop motor skills, hunting strategies, and reflexes critical for survival.

Context: Early mammals were small, nocturnal creatures navigating challenging environments. Play provided a safe context for juveniles to practice vital behaviors, setting the stage for its widespread adoption across the mammalian lineage.

Significance: This foundational stage of play is observed in nearly all modern mammals, including less cognitively complex species like rodents and marsupials, suggesting it evolved as a core adaptive trait in early mammalian history.