Peekaboo!

The urge to make a baby laugh, and the joy we get from it, is no accident. It's a adaptation that makes us rear children in a way that helps them develop the skills they need. At only a few months old, babies laugh when you play peekaboo because they are learning about object permanence. Their laugh is reinforced when you keep doing this pleasurable activity, so they learn to laugh at what they enjoy. But their brains are also forming important concepts. They will continue to laugh at peekaboo for years, but the game later grows into more complicated forms of play that also expand their brains' understanding of the world. This TED-Ed lesson doesn't really go into that pleasurable feedback loop, but spending a weekend with my grandchildren drove it home for me.