A 2.5-million-year-old toolmaking technique may have influenced the evolution of human language and how we teach. The heavy reliance on stone tools by some of our oldest ancestors may have generated evolutionary pressure to develop more advanced ways of transmitting knowledge—such as a primitive proto-language. The findings, published in Nature Communications this week, suggests how Early Stone Age slaughtering tools co-evolved with our ability to communicate.
The oldest-known cutting devices, called Oldowan stone tools, were made by striking a single rock core with a hammerstone to produce several sharp flakes for slicing apart a zebra, for example. This systematic process, called knapping, required maintenance and repair, implying both learning and practice. It was used by Homo habilis and the even older Australopithecus garhi.
Oldowan technology persisted largely unchanged for more than 700,000 years, and this long, drawn-out period of stasis seems inconsistent with the presence of language. After all, "you learn so much faster when someone is telling you what to do," says Thomas Morgan from the University of California, Berkeley. "Our findings suggest that stone tools weren’t just a product of human evolution, but actually drove it as well, creating the evolutionary advantage necessary for the development of modern human communication and teaching.” This may have started to occur some 1.8 million years ago, preceding the advent of the more advanced Acheulean stone tool technology—hand axes and cleavers—around 1.7 million years ago.
Morgan and an international team led by University of Liverpool and University of St. Andrews researchers, conducted an experiment to assess how useful five types of social learning were for creating Oldowan-type tools: reverse engineering, imitation and emulation, basic (non-verbal) teaching, teaching with gestures, and verbal teaching. They recruited 184 college students to produce 6,000 flint pieces. To measure the differing rates of transmission, the volunteers were divided into “learning chains” of up to 10 people. The head of the chain was given a demonstration, raw materials, and five minutes to try their hand at knapping. Then that person showed it to the next person, and so on. The tools were weighed, measured, and judged for quality.
Demonstrations using spoken communication yielded the highest volume and quality of flakes in the least amount of time, with the smallest amount of waste. “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 says in a news release.
Observation alone was a poor way to learn the skill, and selection started favoring teaching and ultimately language. “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 adds. “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.”
Images: Chris Templeton (top), Nature Communications, Laland et al. (middle)