Human language and human conversation might have originated as a way to help our ancestors teach each other tool-making skills, a crucial ability in our evolutionary way forward, researchers say.

Exactly when humans began talking amongst themselves has long been a subject of debate, with estimations ranging from as recently as 50,000 years ago to all the way back to human origins 2 million years in the past.

Spoken words are incapable of leaving any trace in the physical archaeological record -- writing and written evidence would come much later -- so previous studies have concentrated on other indicators, such as early cave art or toolmaking skills, that might serve as similar evidence of symbolic abilities in humans.

However, such evidence has been seen as lacking sufficient evidence to settle the debate on when language first evolved.

Still, the possible link between tool making and language led a team headed by University of California, Berkeley, psychologist Thomas Morgan to attempt an intriguing experiment.

Instead of looking at tool making as possible proxy evidence of language use, they decided to see if language could help modern humans make ancient tools, known as Oldowan tools after the area in Tanzania where they were first uncovered.

Students volunteering for the project were divided into five teams, and the leader of each group was shown how to make a form of tool, a simple stone flake sharp enough to butcher an animal. Early humans were making such tools around 2.5 million years ago. Such flakes require hitting one stone with another stone "hammer" at an exact spot and angle.

In one group students were simply handed a stone, a "hammer" and sample flakes and instructed to try and make their own flake tools. In a second group, members could watch the first person in an attempt to understand the process, but no interaction was allowed.

In the third group, the "teacher" could actively show other group members the process, but without accompanying gestures; in the fourth group the "teacher" could point and gesture but not talk, and in the final group "teachers" could talk to "learners," saying anything required to help.

The results, reported in Nature, were surprising, the researchers said.

Subjects sitting by themselves and attempting to create flake tools simply by looking at their cores, hammers and sample flakes achieved only limited success -- as expected -- but the success rate improved very little among participants who could watch others make the tools.

Only students in the groups where teaching by gesture or speaking were allowed had a significant success rate in creating the flake tools, the researchers found.

Teaching by way of gestures doubled the likelihood of a successful attempt, while verbal teaching yielded a four-fold increase in the success fate, they said.

The findings suggest the successful transmission of even the earliest tool-making technology would likely have needed the capacity for teaching, and probably the beginnings of spoken language in addition, the researchers say.

"The ability to rapidly share the skill to make Oldowan tools would have brought fitness benefits" to early humans, Morgan says, such as greater efficiency in butchering animals, and taken them to another step in human evolutionary progress.

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