Researchers take aim at the evolution of traditional technologies

February 24, 2021

In the last 60,000 years, humans have emerged as an ecologically dominant species and have successfully colonized every terrestrial habitat. Our evolutionary success has been facilitated by a heavy reliance on an ever-advancing technology. Understanding how human technology evolves is crucial to understanding why humans have enjoyed such unprecedented evolutionary success.

Arizona State University doctoral graduate Jacob Harris, working with ASU researcher Robert Boyd and Brian Wood from the University of California, Los Angeles and the Max Planck Institute for Evolutionary Anthropology, is interested in the role of causal knowledge in the manufacture, transmission and, ultimately, the evolution of technology. Causal knowledge is the ability to predict the effect of an intentional modification of a system, like the design and manufacture of traditional bow-and-arrow technology — the focus of their investigation. Hadza hunter Hadza hunter with bow. Image courtesy of Jacob Harris. Download Full Image

Prior research on causal knowledge has been restricted to theoretical work and experimental studies with student participants. Harris and Wood lived and worked with Hadza hunters for several months and interviewed them about bow manufacture and use. The Hadza are contemporary hunter-gathers who live in north-central Tanzania. There are currently around 1,200 speakers of the Hadza language distributed across a wide region, with local groups varying in the total fraction of their diet that is derived from hunting and gathering. However, even among those groups that forage the least, the manufacture and use of bow and arrow technology is a vibrant and daily practice among men.

The research, published this week in the journal Current Biology, addresses two competing theories in human evolution. The "cognitive niche" hypothesis proposes that innovations typically arise and are then refined over the course of a single lifetime, rather than generations, and if environments change people rapidly adapt. Proponents of this hypothesis argue that innovation and transmission require causal understanding. The "cultural niche" hypothesis holds that cultural elements often accumulate and recombine without a causal understanding by those who use them.

Hadza bowyers (bow makers) provide a rare opportunity to evaluate these models in a naturalistic setting involving one of the most significant technologies in human evolution — the bow and arrow.

Harris and Wood interviewed 64 highly skilled Hadza bowyers between the ages of 15 and 77 from five different camps regarding bow manufacture and use. Subjects were asked questions about their bows and asked to predict how minor modifications would affect either arrow speed or noise production. Queries included questions such as, “Will an increase in draw weight (strength of pull) result in the arrow traveling faster, slower or no change?” and “Will an increase in brace height — the distance from the bowstring to the inside of the bow — result in the arrow traveling faster, slower or no change?”

Hadza man with bow

Hadza man with bow. Image courtesy of Jacob Harris.

“When making a bow, the bowyer confronts a series of complex trade-offs, and his design choices represent one possible solution out of a large number of possibilities,” Harris said. “The Hadza bow represents an elegant solution to an exceptionally complex optimization problem. Their bows are extremely versatile, capable of killing a wide range of prey and functioning in a variety of environments.” Harris conducted this research while a postdoctoral researcher at the University of California, Los Angeles.

The research findings suggest that the Hadza study participants are able to manufacture and transmit bow-making technology with only partial causal knowledge. It appears that some of the design choices made by Hadza bowyers are constrained by cultural norms rather than a desire to optimize performance. They also found that causal knowledge does not correlate with age. In other words, individuals don’t appear to acquire a more complete causal schema as they grow older.

“Hadza bowyers construct powerful bows from local materials and use them to hunt a wide variety of prey. Over 95% of Hadza men possess a bow, and hunters use their bows to provide the majority of the meat in their diet and therefore, represent a vital aspect of the Hadza economy,” Wood said. “Hadza men begin using bows at a very early age. Boys as young as 3 years old mimic the manufacturing behaviors of their elders and begin manufacturing their own bows. By early adulthood they are highly proficient bowyers and hunters.”

There is also no evidence that some individuals are significantly more knowledgeable than others. Prior research reported the presence of socially acknowledged “experts” in areas such as hunting, honey gathering and arrow making. However, bow-making skill, as perceived by Hadza bowyers, does not appear to be predicated on exceptional cause-and-effect knowledge of bow mechanics.

“The evolution of complex technologies, such as the bow, can occur with only partial causal understanding and has significant implications for our understanding of the cultural evolution of technology. It suggests that the human proclivity to rely upon cumulative culture rather than individual expertise likely has deep evolutionary roots,” said Boyd, professor in the School of Human Evolution and Social Change and research affiliate with the Institute of Human Origins.

“A more holistic understanding of technological evolution is necessary, one that does not view these two competing models as mutually exclusive. In our study, we found evidence to suggest that a complete causal understanding is not necessary, but we also identified key aspects of Hadza projectile technology that were more likely to be associated with causal knowledge,” Harris said.

The researchers will continue their investigation into which aspects of this technology are more likely to be associated with and without causal knowledge and explore the degree to which these are learned though experience and/or through direct (active teaching) or indirect (observation) transmission. Their research will contribute to the development of a more holistic theoretical model that accounts for the relative roles of multiple influences, including culture, causal knowledge and environmental constraints, such as resource availability.

This research was published as “The role of causal knowledge in the evolution of traditional technology,” in Current Biology, Jacob A. Harris, Robert Boyd, Brian M. Wood.

Julie Russ

Assistant director, Institute of Human Origins


Can technology improve even though people don’t understand what they are doing?

April 1, 2019

Beginning about 60,000 years ago, our species spread across the world occupying a wider range of habitats than any other species. Humans can do this because we can rapidly evolve specialized tools that make life possible in different environments — kayaks in the Arctic and fishing weirs in the Amazon. How are we able to do this? Most scholars focus on our intelligence: People are better at causal reasoning than other animals, and this allows us to invent useful tools.

New experimental work by an Arizona State University research team published in the journal Nature Human Behaviour this week suggests that cultural evolution can generate new adaptive knowledge even though people don’t understand what they are doing. The research team includes School of Human Evolution and Social Change Origins Professor and Institute of Human Origins research affiliate Rob Boyd and former Institute of Human Origins postdoctoral researcher Maxime Derex. Participant viewing wheel Participants were shown a wheel with four spokes resting on an inclined ramp. The task was to adjust the position of the weights so that the wheel rolled to the bottom of the ramp as quickly as possible. Image by Maxime Derex Download Full Image

Even in traditional societies, human technology is often too complex to be the product of human ingenuity alone. The “cultural niche” hypothesis suggests that complex technologies result from the accumulation of many, mostly small and often poorly understood, improvements made across generations linked by cultural transmission.

To test the researchers’ hypothesis that beneficial changes over generations can produce cultural adaptations without individual understanding, the team studied cultural evolution in the laboratory with an exercise to simulate “generations” of improvements.

In the first section of the experiment, participants were shown a wheel with four spokes resting on an inclined ramp. On each spoke there was a weight that could be move closer or further from the hub of the wheel. The task was to adjust the position of the weights so that the wheel rolled to the bottom of the ramp as quickly as possible. Participants were arranged in 14 groups or “transmission chains,” with each chain five participants long.

In each chain, the first participant got a few trials to experiment with the weights to improve how fast the wheel went down the ramp. The second, third, fourth and fifth participant in the chain got see to how the previous participant adjusted the weights and then had a few trials to experiment. Averaged over 14 groups of participants, the results got better and better and, at the end of the last group, the wheels were going almost as fast as possible.

But this happened without any increase in understanding. After the experiment, each participant was given a test of causal understanding and asked which of two wheels with weights in different positions was faster.

However, there was no progress in understanding. Participants got better at the task even though their understanding did not improve. The first participant’s responses were only slightly better than random choices, and the fifth participants had no better understanding than the first participant on average.

Was the problem that participants could only observe what the previous member of the chain did, not why they did what they did? A second experiment shows that this is not the case.

In a second version, participants were able to provide a written explanation of why they positioned the weights where they did. However, there was still no systematic improvement in understanding.

Some participants had part of the explanation, but not the whole causal story.

“Most participants actually produced incorrect or incomplete theories despite the relative simplicity of the physical system,” said Derex, now the Marie Curie Fellow at the University of Exeter in England. “This constrained subsequent experimentation and prevented participants from discovering more efficient solutions.”

This experiment helps explain how cultural evolution generates very complex tools even in simple, preliterate societies. Constructions of a kayak or fishing weir are complex, multistage processes that are hard to understand even with the help of modern science. Nonetheless, these technologies and many, many others were devised by people living in small villages without libraries, computers or laboratories.

“Of course, intelligence is important for human adaptation,” said Boyd. “But it is not enough. Our unique ability to learn from each other makes possible the cumulative cultural evolution of superb adaptations — that are at best only partially understood — and this powerful tool has allowed our species to adapt and spread.”

Julie Russ

Assistant director, Institute of Human Origins