A far from definite, yet highly interesting explanation for the origin of language was recently proposed – not by linguists or geneticists, but by a psychologists who took an archaeological route. Thomas Morgan, a psychologist at the University of California, Berkeley presents us with a chicken or the egg dilemma: was tool use proliferated by language or was language evolutionary triggered by the need to proliferate tool use? The findings appeared in Nature. 

The tools of language

Oldowan chopping flint dated from the Lower Paleolithic 900,000 years ago. Credit: World Museum of Man

The debate over the origin of speech is long from over. Estimates range from as early 50,000 years ago to some 2 million years ago when the human genus as we know it first emerged. Unfortunately, words don’t leave fossil records and as such there’s room for much speculation. To unravel the mystery, researchers often focus their attention on proxies for language emergence like early art of sophisticated tool making. The latter caught Morgan’s attention, yet unlike his predecessors he approached the question in a novel manner.

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Him and colleagues recruited 184 students from the University of St. Andrews in the United Kingdom and organized them into five groups. One person from each group was taught how to make Oldowan tools, which include fairly simple stone flakes that were manufactured by early humans beginning about 2.5 million years ago. This makes the Oldowan  the oldest-known stone tool industry, and as such an important milestone in human evolutionary history: the earliest evidence of cultural behavior. Homo habilis, an ancestor of Homo sapiens, was the first hominid to manufacture Oldowan tools. To make an Oldowan cutting tool, you need to hit a stone “core” with a stone “hammer” in such a way that a flake sharp enough to butcher an animal is struck off.

All groups were directed to build their own Oldowan tools, but each was taught how to do make them with different approaches.

• Group #1: volunteers were shown finished flakes, then given core and hammer. They left to themselves with no further instructions;
• Group #2: students learned how to make the tools just by watching the leading volunteer while he manufactured the flake, but with no other interactions;
• Group #3: subjects worked together and actively showed each other how to build the flakes, but without gesturing;
• Group #4: students were allowed to gesture and point, but no talking was allowed;
• Group #5: leaders were allowed to talk and instruct apprentices as long and as much as they needed;

(a) A diagram of the stone knapping process. The hammerstone strikes the core with the goal of producing the flake. The platform edge and angle are important to the success of knapping. (b-f) the five learning conditions. (g) The structureof the experiment. For each condition, six chanins were carried out (Four short and two long); one of two trained experimenters started each chain (equally with each condition). Credit: Morgan et all // Nature

The experiment tried to follow a natural path of skill transmission as possible, as each apprentice, once he acquired the necessary skills, became a teacher. In total, five different chains of transmission were demonstrated, which resulted in 5,000 completed Oldowan flakes. As expected, the students were left to themselves with no instructions performed the worse. Those who watched others how they built they tools performed mildly better. In fact, only those groups who were allowed to gesture or talk performed significantly better than the previous reverse engineering baselines. Performance was gauged based on several indicators of stone tool making like: the total number of  flakes produced that were long enough and sharp enough to be viable and the proportion of hits that resulted in a viable flake. Gestural teaching doubled and verbal teaching quadrupled the likelihood that a single strike would result in a viable flake, the team found.

“If someone is trying to learn a skill that has lots of subtlety to it, it helps to engage with a teacher and have them correct you,” Morgan said. “You learn so much faster when someone is telling you what to do.”

As for what the results mean for the Oldowan hominins: “They were probably not talking,” Morgan said. “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.”

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Yet, for tool making to spread across vast communities of hominids you necessarily need a teaching system in place. Gestures work pretty well, but we can assume there was also some kind of protolanguage. As tools became more and more important, so did the need for conveying knowledge on how these are built. The ability to rapidly share the skill to make Oldowan tools would have brought fitness benefits” to early humans, Morgan says. Natural selection would soon come at play and improve on primitive language abilities. Eventually, a semantically rich language emerged. This hypothesis seems to be validated by the next generation of tools –  the advent of Acheulean hand-axes and cleavers some 1.7 million years ago.

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

“At some point they reached a threshold level of communication that allowed Acheulean hand axes to start being taught and spread around successfully and that almost certainly involved some sort of teaching and proto-type language,” Morgan said.

Some scientists, have criticized the study however. Ceri Shipton, an archaeologist at the University of Cambridge in the United Kingdom, believes Morgan’s paper “overreaches in its interpretations” because the subjects had grown up with language, but have not grown up with stone tools. Dietrich Stout, an archaeologist at Emory University in Atlanta argues that the participants were given far too less time to learn the Oldowan craft: 5 minutes to learn the toolmaking techniques, and then no more than 25 minutes to produce Oldowan flakes. Had they been given more time, Stout believes the differences in the five methods of transmission would have become largely indistinguishable.

Nevertheless, it’s an exciting paper. The debate ensues and this is far from being the last thing we’ll learn about the origin of language.