Washington, April 1 (IANS): At some point of time 50,000 to 100,000 years ago, humans began talking to one another in a uniquely complex form -- that likely developed quite rapidly into a sophisticated language system, a new research suggests.

Instead of mumbles and grunts, people deployed syntax and structures resembling the ones we use today, said a new paper from Massachusetts Institute of Technology (MIT) that appeared in the peer-reviewed journal Frontiers in Psychology.

"The hierarchical complexity found in present-day language is likely to have been present in human language since its emergence," explained Shigeru Miyagawa, professor of linguistics at MIT.

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, pre-syntax stage," Miyagawa added.

Miyagawa has an alternate hypothesis about what created human language. Humans alone 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.

In the paper, the authors wrote that a single word can be "internally complex, often as complex as an entire phrase", making it less likely that words we use today are descended from a pre-syntax mode of speech.

Take the word "nationalization". It starts with "nation," a noun; adds "-al" to create an adjective; adds "-iz (a)" to form a verb; and ends with "-tion," to form another noun but with a new meaning.

"Hierarchical structure is present not only in single words, but also in compounds, which, contrary to the claims of some, are not the structureless fossilised form of a prior stage," Miyagawa said.

This school of thought holds that languages have blended expressive and lexical layers through a system called "Merge".

"Once 'Merge' has applied integrating these two layers, we have essentially all the features of a full-fledged human language," Miyagawa said.