I just saw my unborn son yawn in the womb on an ultrasound today so this brings me a bit of silly joy - knowing his brain folds are just developing and he might be cooling them! That said, the stats nerd in me doesn’t buy this study outright.

I’d personally hypothesize that yawns, like almost all other emotional displays (smiling, laughing, worrying, eye dilation) are simple pre-language communications. It’s useful for a pack of animals to know when one animal is tired - yawning is contagious because it’s advantageous for the pack to have a similar sleep schedule - and to be aware of how each other feels. Our faces display our emotions clearly as a form of communication to others. We developed whites in our eyes, for example, so we can track the attention of our pack-mates. It's easy to forget that biologically, spoken language is a brand new invention - but communication is extremely ancient.