Thanks to a temp. teaching job at the Amsterdam University College, I read this article:
“Play in evolution and development” by Anthony D. Pellegrini, Danielle Dupuis and Peter K. Smith.
I love for instance this quote: “… leading us to posit that play may be an important mechanism at the vanguard of behavioral innovation” in this article a lot more reasoning on the how and why. Read the complete article, or ask me next time we talk ; )