Why do babies babble?

Babies babble because they are practising the building blocks of their language before they have any words to put them in. Babbling is a stage of language learning in which an infant plays with speech sounds without yet saying anything recognizable. It is not random noise: babies copy the melody and rhythm of the language around them, and babble mostly with the consonants and vowels that language uses most.

The mechanics are surprisingly simple. Around six months, babies start the 'canonical' stage, producing strings like 'bababa'. That pattern comes from the jaw going up and down with the voice on: jaw up makes a consonant, jaw down makes a vowel. By about ten months, the babble has adult-like stress and intonation, which is why a baby can sound like it is chatting in a language you almost understand. First words usually come around twelve months.

Adults shape the process. Of all the babbled syllables, parents seize on a few, like 'ma ma' and 'da da', treat them as words and cheer, and babies watch those reactions closely. The most striking clue came from deaf babies raised with sign language: the neuroscientist Laura-Ann Petitto showed that they babble with their hands, in the same rhythmic syllables. Babbling, it turns out, is about language itself, not just sound.