All work & no play make Jack not only dull, but also evolutionarily disadvantaged…
QUICK NOTE: The most commonly-cited explanation for animal play (practicing direct analogs of survival behavior) doesn’t square with all the evidence. Check out this paper: http://www.sciencedirect.com/science/article/pii/S0163104780924565
Taking Play Seriously, by Robin Marantz Henig - http://www.nytimes.com/2008/02/17/magazine/17play.html?pagewanted=all
Juvenile peer play experience and the development of the orbitofrontal and medial prefrontal cortices (Bell, Pellis, & Kolb 2009) - http://www.sciencedirect.com/science/article/pii/S0166432809005609
More Play, Please - The Perspective of Kindergarten Teachers on Play in the Classroom (Lynch 2015) - http://www.journalofplay.org/sites/www.journalofplay.org/files/pdf-articles/7-3-article-more-play-please.pdf
Vygotsky Meets Neuroscience - The Cerebellum and the Rise of Culture through Play (Vandervert 2015) http://www.journalofplay.org/sites/www.journalofplay.org/files/pdf-articles/9-2-article-3-vygotsky-meets-neuroscience.pdf
Plans Unveiled for Star Wars-Inspired Themed Resort at Walt Disney World, by Jennifer Fickley-Baker - https://disneyparks.disney.go.com/blog/2017/07/plans-unveiled-for-star-wars-inspired-themed-resort-at-walt-disney-world/
The National Institute for Play, a nonprofit dedicated to advocating play for adults & children - http://www.nifplay.org/science/pattern-play/
Symbolic Play: The Development of Social Understanding (Bretherton 1984) - https://goo.gl/J1hMxe
The Ambiguity of Play (Sutton-Smith, 1987) - https://goo.gl/H7oZNz
How Play Makes for a More Adaptable Brain, a Comparative & Neural Perspective (Pellis, Pellis, & Himmler 2015) - http://files.eric.ed.gov/fulltext/EJ1043959.pdf
The Nature of Play - An Overview (Henricks 2008) - http://www.journalofplay.org/sites/www.journalofplay.org/files/pdf-articles/1-2-article-the-nature-of-play.pdf
Animal Play: Evolutionary, Comparative, and Ecological Perspectives (Summary by Bekoff & Beyers, 1998) - http://cogweb.ucla.edu/Abstracts/Bekoff_Byers_98.html
Examining playfulness in adults: Testing its correlates with personality, positive psychological functioning, goal aspirations, and multi-methodically assessed ingenuity (Proyer 2012) - http://www.psychologie-aktuell.com/fileadmin/download/ptam/2-2012_20120628/01_proyer.pdf