This is a reasonable and somewhat popular theory but evidence to support it is harder to find than you might imagine. People have spent their entire lives study

This is a reasonable and somewhat popular theory but evidence to support it is harder to find than you might imagine. People have spent their entire lives studying animal behavior and still don't have much more than a shrug to show for evidence supporting play as a survival or evolutionary mechanism. Some play does look like hunting (cat and dog owners will notice this), but there's a good amount that also doesn't align with anything else an animal regularly does.