This story originally appeared in the September 2014 issue of mental_floss magazine. Subscribe to our print edition here, and our iPad edition here.

This question is for the birds. No, really! In a paper recently published in Frontiers in Psychology, linguists at MIT and the University of Tokyo argue that ancient humans crafted language from two communication systems that already existed in nature—those used by birds and primates.

Human language has two distinct layers: expressive and lexical. Both of these have existed in nature for millennia. The melodic, beat-stressed expressive quality of our language is similar to that used by birds. The lexical “pragmatic, content-carrying parts of speech” resemble the system used by other primates. About 100,000 years ago, the research suggests, humans may have fused the two together to form the building blocks of their own language. In doing so, they achieved something astounding. Birdsong and primate language are both finite: They each contain only a limited number of sounds, which supply a limited number of meanings. But by combining the two, humans created a language that allows for infinite possible meaning combinations. This complexity is part of what makes us, well, human.