Have you ever witnessed a kid do something so adorable you wondered whether there might be an evolutionary explanation for the behavior that offers insight into the human mind and the origins of language?

British sociologists Gillian Forrester and Alina Rodriguez have. In a study for the August issue of the journal Cognition, they delve deep into the biological underpinnings of one of kids’ cutest quirks: their tendency to stick their tongues out when they concentrate.

It turns out that the “tongue protrusions” are leftovers from the most primitive beginnings of human speech.

To figure out how this habit came to be, Forrester and Rodriguez rallied a group of 14 four-year-olds and set them to work at various difficult tasks: recalling a story, experimenting with a lock and key, playing a hand game with a researcher. In all of them, the kids stuck out their tongues during moments of intense thought — a result in keeping with past research, which has established that the behavior is common in children before they hit puberty.

But when reviewing videotape of the silly-looking pre-schoolers, the scientists came to a fairly weighty realization: The kids stuck their tongues out the most not when performing the challenging fine motor activities (opening a padlock, playing with very small dolls) but during the hand game activity, which the sociologists called “knock and tap.”

This is no an accident, they argue. The game — which involves the kids tapping a table when a researcher knocks on it, and knocking when she taps — requires coordination, quick-thinking, gestures and the ability to negotiate rules, all the building blocks of communication. Perhaps the “tongue protrusion” phenomenon, as the researchers call it, is evidence left over from the early development of language, when gestures (like knocking and tapping) evolved into speech (which takes a tongue.)

That theory meshes with a second finding from Forrester and Rodriguez’s study: The tongue protrusions tended to be biased toward the right during some tasks, indicating that they are controlled by the left hemisphere of the brain. This is the side responsible for processing language, boosting the researchers’ belief that the tongue protrusions are related to the same aspects of the brain that help us communicate.

Sticking your tongue out is not just a kid thing — the study notes that adults also perform unconscious mouth movements while performing manual tasks, but that we’ve mostly learned to suppress them for reasons related to not looking ridiculous in public.

But, the researchers say, further study of the tongue phenomenon could “drive new investigations regarding how an early human communication system transitioned from hand to mouth.”

Maybe we should let ourselves stick our tongues out more often. You know, for the sake of science.