If you’ve ever cooed at a baby, you have participated in a very special experience. Indeed, it’s an all but unique one: Whereas humans constantly chatter to their infants, other apes hardly ever do so, a new study reveals.

“It’s a new feature that has evolved and massively expanded in our species,” said Johanna Schick, a linguist at the University of Zurich and an author of the study. And that expansion, Dr. Schick and her colleagues argue, may have been crucial to the evolution of language.

Other mammals can bark, meow, roar and hoot. But no other species can use a set of sounds to produce words, nor build sentences with those words to convey an infinite variety of meaning. To trace the origin of our gift of language, researchers often study apes, our closest living relatives.

These studies hint that some of the ingredients of language had already evolved in the ancestors we share with living apes, which lived millions of years ago. Chimpanzees can make dozens of distinct calls, for example, which they can join into pairs to communicate new things. Building meaning from smaller units is what lets us create sentences from words.