At some point, probably 50,000 to 100,000 years ago, humans began talking to one another in a uniquely complex form. It is easy to imagine this epochal change as cavemen grunting, or hunter-gatherers mumbling and pointing. But in a new paper, an MIT linguist contends that human language likely developed quite rapidly into a sophisticated system: Instead of mumbles and grunts, people deployed syntax and structures resembling the ones we use today. "The hierarchical complexity found in present-day language is likely to have been present in human language since its emergence," says Shigeru Miyagawa, Professor of Linguistics and the Kochi Prefecture-John Manjiro Professor in Japanese Language and Culture at MIT, and a co-author of the new paper on the subject.

To be clear, this is not a universally accepted claim: Many scholars believe that humans first started using a kind of "proto-language" -- a rudimentary, primitive kind of communication with only a gradual development of words and syntax. But Miyagawa thinks this is not the case. Single words, he believes, bear traces of syntax showing that they must be descended from an older, syntax-laden system, rather than from simple, primal utterances.

"Since we can find syntax within words, there is no reason to consider them as 'linguistic fossils' of a prior, presyntax stage," Miyagawa adds.

Miyagawa has an alternate hypothesis about what created human language: Humans alone, as he has asserted in papers published in recent years, have combined an "expressive" layer of language, as seen in birdsong, with a "lexical" layer, as seen in monkeys who utter isolated sounds with real-world meaning, such as alarm calls. Miyagawa's "integration hypothesis" holds that whatever first caused them, these layers of language blended quickly and successfully.