The science of psychology is the empirical study of feelings, thoughts, and/or behavior. Among playtime psychologists, there has been a growing emphasis on the mental mechanisms that underlie individual and collective play behavior and on the confluence or variation within and between various cultures, at various times and places. Thus, many scholars distinguish between play that is contextual and relative to time/place and play behavior that is timeless and universal. And, there is much scholarly debate over the appropriate role for adults in shaping childhood play.
A good introduction to play as it relates to psychology and brain science can be found in Play: How It Shapes the Brain, Opens the Imagination, and Invigorates the Soul, written by Stuart Brown with Christopher Vaughan. Among the excellent works that explore child’s play and developmental psychology are Play and Child Development, by Joe Frost, Sue Wortham, and Stuart Reifel, which was first published two decades ago and is now in its fourth edition, and Sergio Pellis and Vivian Pellis’s The Playful Brain: Venturing to the Limits of Neuroscience. Those seeking a good head start on the relationship between play, developmental psychology, and therapy should seek out Sandra Walker Russ’s Play in Child Development and Psychotherapy: Toward Empirically Supported Practice and Miguel Sicart’s Play Matters, a relatively recent release in MIT’s “Playful Thinking” series.1
Recently psychologists have begun to integrate the findings of history, psychology, and biology under the banner of evolutionary psychology. Evolutionary psychologists distinguish between proximate and ultimate theories of human behavior. Proximate theories address questions of where, when, and how humans behave; ultimate theories explain why humans and other species behave as they do, in terms of Darwinian evolution (variation and selection). Most playtime scholars cite Peter Gray as one of the early proponents of applying evolutionary psychology to child’s play. In his Free to Learn: Why Unleashing the Instinct to Play Will Make Our Children Happier, More Self-Reliant, and Better Students for Life, Gray is persuasive in arguing for more child-directed play in a mixed-age learning environment. He followed up this work with the collection Ancestral Landscapes in Human Evolution: Culture, Childrearing and Social Wellbeing, in which he joined coeditors Darcia Narvaez, Kristin Valentino, Agustin Fuentes, and James McKenna. Also valuable in this context is David Elkind’s The Power of Play, discussed earlier in this essay.
Many evolutionary psychologists specialize in animal behavior, and therefore explore play in various species, human and nonhuman. Broad accounts of play among animals of different species are available in Animal Play: Evolutionary, Comparative, and Ecological Perspectives, edited by Marc Bekoff and John Byers, and Thomas Power’s Play and Exploration in Children and Animals. Both are a bit older but nevertheless worthwhile. A slightly more recent account of play in various species is Gordon Burghardt’s The Genesis of Animal Play: Testing the Limits, which focuses on how and why play evolved among mammals, birds, reptiles, fish, and invertebrates. And Dario Maestripieri’s fine Games Primates Play: An Undercover Investigation of the Evolution and Economics of Human Relationships focuses on parallels between human and nonhuman primate behavior and play.2
1. Also valuable is Curiosity, Pleasure and Play: A Neurodevelopmental Perspective, by Bruce Perry, Lean Hogan, and Sarah Martin, published in the haaeyc 9 Advocate August 2000, available in pdf at http://chinadevpeds.com/resources/CuriosityPleasurePlay_Perry.pdf.
2. Along these same lines in the journal literature is Ellen Beate Sandseter and Leif Edward Otteson Kennair’s “Children’s Risky Play from an Evolutionary Perspective: The Anti-Phobic Effects of Thrilling Experiences.” Evolutionary Psychology 9 (2), 2011 https://journals.sagepub.com/doi/10.1177/147470491100900212
Play and Exploration in Children and Animals by 
