It’s widely understood that human genetics can influence culture, but increasingly, the idea that culture can also affect genetics is gaining ground. The theory of gene-culture coevolution suggests that “the cultural practices we adopt change the costs and benefits of having certain genes,” explains Catharine Cross, a researcher at the University of St Andrews. “A gene that is advantageous under one cultural practice is not necessarily advantageous under another.”

For example, yam cultivation in West Africa led to deforestation and an increase in standing water, which creates a breeding ground for mosquitoes and malaria. This meant that yam farmers with a particular genetic resistance to malaria were more likely to survive than farmers with susceptibility to malaria. Yam farmers in the region have been found to have a higher incidence of this genetic trait than nearby groups—even speakers of the same language—who farm other crops.

A recent study published in Nature Communications has suggested that stone tool-making practices among the ancestors of modern humans may have put evolutionary pressure on individuals who weren’t very good at communicating, helping to select for the genes that would become involved in language. The study found that the use of verbal teaching, compared to learning by imitation, significantly improved the quality and speed production of stone tools. This suggests that individuals with gestural or verbal communication skills could have learned to make tools faster and better, giving them an advantage over individuals who could only imitate.

Playing telephone with stone tools

The researchers tested the difference in performance by using “transmission chains”, a method similar to the children’s game of telephone. The person who starts a chain passes on information to the next person, who then passes that information along, all the way down the chain. This can provide insight into how information changes when it is passed through generations of people.

In this case, the information being passed down the chain was the technique of creating Oldowan stone tools. These were the first stone tools to appear in the fossil record, approximately 2.5 million years ago, and were the predominant technology for approximately 700,000 years until more advanced Acheulean stone tools started to appear.

The first person in each chain was an experimenter skilled in the Oldowan method of hammering sharp flakes of flint off a central core. This person could pass information down the transmission chain in one of five ways. The first method, pure imitation, involved the teacher simply making the tools while the first participant watched, with no interaction. Three of the five transmission methods involved some sort of interaction: basic teaching, which allowed the teacher to slow their movements down or shape the participant’s grip; gestural teaching, which added in gestures; or verbal teaching, which allowed normal speech. Finally, the fifth method allowed the participant no contact at all with the teacher—rather, they had to work out how to make the tools just by looking at examples produced by the teacher.

After a short learning period, the participant was required to pass on their new skills to the next participant in the chain using the same transmission method. Participants were paid more if they and their pupils produced more, higher-quality tools, so there was a strong motivation to learn and teach well. Each learning condition had six transmission chains, with 184 participants overall.

The results indicated that learning through teaching, rather than reverse engineering or imitation, had a marked influence on the results. Participants who experienced active instruction from their teachers produced more, better quality flakes at a higher speed, with fewer mistakes. Unsurprisingly, verbal instruction produced the best results, followed by gestural instruction and then basic teaching.

Pressure to communicate

The results are important, write the researchers, because they help us to understand the language could have played in human ancestors during the period when Oldowan tools were in use. It’s unlikely that Oldowan tools would have remained unchanged for 700,000 years if language had already emerged, they write. This suggests that imitation, which doesn't transmit information as efficiently, helped to maintain this long period of stasis. However, it also seems that individuals with better communicative abilities may have had better success at tool-making, contributing to the pressures that led to the evolution of language, and more advanced Acheulean tools.

“This is a rigorously conducted study and a nice advance on previous studies,” says Dr Alex Mesoudi, who researches cultural evolution at Durham University, and was not involved in the research. “There are very few experiments using genuine stone tools; many use computer simulations or some even use polystyrene blocks. Using actual stone is a step forward.”

There are certain limitations, he notes, most importantly the very short time available to participants to learn the process—in reality these techniques would have taken years to master. However, the study does show an advantage to teaching if you have the same amount of time for all the different learning methods, he adds.

It’s important not to over-extrapolate from these results, says Cross, one of the authors of the paper. “We’re not saying that what definitely happened is that tools came first, and then caused language to come along. Rather, we think that the capacity for tool-use and the capacity for language evolved together, and that we can see a benefit to verbal teaching over a limited time period.”

A potential future avenue for research is cross-cultural exploration, suggests Mesoudi. His own recent work has found that Chinese participants imitate more than British participants, suggesting that imitation may not be the same universally. This could mean that learning based on imitation could have more success in other cultures, he suggests.

Nature Communications, 2015. DOI: 10.1038/ncomms7029 (About DOIs).