Peekaboo is a game played over the world, crossing language and cultural barriers. Why is it so universal? Perhaps because it’s such a powerful learning tool.
Babies don't read books, and they don't know that many people, so thesurprising durability and cultural universality of peekaboo is perhaps a clue that it taps into something fundamental in their minds. No mere habit or fashion, the game can help show us the foundations on which adult human thought is built.
Peekaboo uses the fundamental structure of all good jokes - surprise, balanced with expectation. Researchers showed this in tests involving a group of six-, seven- and eight-month-olds which sound like more fun than a psychology experiment should be. Most of the time the peekaboo game proceeded normally, however on occasion the adult hid and reappeared as a different adult, or hid and reappeared in a different location. Videos of the infants were rated by independent observers for how much the babies smiled and laughed.
On these “trick trials” the babies smiled and laughed less, even though the outcome was more surprising. What's more, the difference between their enjoyment of normal peekaboo and trick-peekaboo increased with age (with the eight-month-olds enjoying the trick trials least). The researchers' interpretation for this is that the game relies on being able to predict the outcome. As the babies get older their prediction gets stronger, so the discrepancy with what actually happens gets larger - they find it less and less funny.
The secret to the enduring popularity of peekaboo is that it isn't actually a single game. As the baby gets older their carer lets the game adapt to the babies' new abilities, allowing both adult and infant to enjoy a similar game but done in different ways. The earliest version of peekaboo is simple looming, where the carer announces they are coming with their voice before bringing their face into close focus for the baby. As the baby gets older they can enjoy the adult hiding and reappearing, but after a year or so they can graduate to take control by hiding and reappearing themselves.
In this way peekaboo can keep giving, allowing a perfect balance of what a developing baby knows about the world, what they are able to control and what they are still surprised by. Thankfully we adults enjoy their laughter so much that the repetition does nothing to stop us enjoying endless rounds of the game ourselves.