Sometime around two million years ago, a primitive proto-language was invented. And researchers say the first topic of conversation was almost certainly rock -- not just any old boulder, but the rocks early man was turning into tools.

An international team of researchers -- including experts in the fields of archaeology, evolutionary biology and psychology -- compiled evidence suggesting the spread of tool making and stone technology wouldn't have been possible without at least some form of basic communication.

Researchers tested the process of teaching and sharing stone making techniques among groups of study volunteers, a 10-person chain tasked with passing knowledge down the line like a game of telephone. As predicted, those allowed to use language were able to share the information faster and more accurately.

The study involved the teaching of Oldowan stone-knapping skills, the earliest known method of tool production -- one that dates back to the Lower Paleolithic period in eastern Africa. The earliest known Oldowan tools date to 2.6 million years ago, found in present day Ethiopia. The tools made their way down to southern Africa and eventually into Asia and Europe, but the technology remained largely the same for 700,000 years until more sophisticated Acheulean hand-axes and cleavers began appearing in the archaeological record.

Our earliest human ancestors -- the ones who remained satisfied with Oldowan technology for nearly a million years -- likely didn't have language. But Acheulean technology, the scientists suggest in their new study, likely evolved alongside language.

"They were probably not talking," lead study author Dr. Thomas Morgan, a researcher in psychology at the University of California, Berkeley, said of the Oldowan hominins in a recent press release. "These tools are the only tools they made for 700,000 years. So if people had language, they would have learned faster and developed newer technologies more rapidly."

But Morgan and his colleagues -- including researchers from Scotland's University of St. Andrews, as well as England's University of Liverpool and University College London -- the leap from Oldowan to Acheulean technology required the advent of basic communication.

"To sustain Acheulean technology, there must have been some kind of teaching, and maybe even a kind of language, going on," Morgan added, "even just a simple proto-language using sounds or gestures for 'yes' or 'no,' or 'here' or 'there.'"

And it was the need to distribute this information that encouraged language, researchers say, just as much as language encouraged technological advancements.

The new research was published this week in the journal Nature Communications.