From curiosity to play: re-evaluating the evolutionary origins of play.

The origins of play remain a profound puzzle in animal evolution. Play is often characterised as a seemingly non-functional behaviour that confers little survival or reproductive benefit. This characteristic makes the evolution of play appear paradoxical under Darwinian principles, which posit that traits must be beneficial to be selected. Given that the adaptive benefits are unclear even for the well-established forms of play in extant animals, it seems improbable that an incipient form of play in the earliest stages of evolution emerged due to a decisive selective advantage. The conventional view that has gained traction suggests that play evolved not as an adaptive trait but as a by-product of energetic, ontogenetic, ecological, and psychological facilitating factors. Building upon previous empirical and theoretical studies, this review discusses the evolutionary relationship between play and exploration. More specifically, it argues that relying on the classification dividing exploration into intrinsic and extrinsic types can help us articulate both the evolutionary and mechanistic continuities and discontinuities between play and exploration. Based on this distinction, this article proposes the following hypothesis: play originally evolved as a by-product of curiosity-motivated intrinsic exploration. This hypothesis is supported by recent empirical evidence indicating that play may have evolved by co-opting some of the mechanisms of curiosity, including (i) the commonality between stimuli that elicit curiosity and those that elicit play, and (ii) the shared neural basis of curiosity and play involving the reward and executive control systems. I also discuss new testable predictions derived from this hypothesis and outline future research directions, including comparative phylogenetic studies, eco-sociological analyses, and psycho-behavioural approaches.