Technological advances have been key to the success of Earth's most dominant and ecologically adaptable species: modern humans.

In an effort to make sense of Homo sapiens' remarkable evolutionary success, the authors of a new paper set out to illuminate the importance of causal knowledge in the manufacture, transmission and evolution of technology.

Causal knowledge describes an understanding of how deliberate modifications will alter a tool or technological systems.

For the new study, published Wednesday in the journal Current Biology, an international team of researchers analyzed the deployment of causal knowledge among bow-and-arrow-wielding Hadza hunters.

The Hadza people are an indigenous group of hunter-gatherers in north-central Tanzania.

About 400 of the more than 1,200 Hadza people living in Tanzania still subsist entirely on traditional means of foraging, but the construction and use of bow-and-arrow technology remains an important daily ritual for most Hadza hunters.

Researchers from Arizona State, UCLA and the Max Planck Institute, in Germany, spent several months with different Hadza groups, studying the manufacture and transmission of this technology.

The time spent with Hadza hunters allowed scientists to consider two theories of human evolution: the cognitive niche hypothesis and the cultural niche hypothesis.

The cognitive niche hypothesis maintains that humans use causal knowledge to develop and refine technology innovations across a single lifetime.

According to the cognitive niche hypothesis, causal knowledge allowed humans and their technologies to quickly adapt to changing environments.

The cultural niche hypothesis insist innovation is more haphazard and less purposeful. Proponents of the hypothesis argue cultural practices accumulate and recombine over time to yield technological innovations -- no causal understanding necessary.

While living and working with Hadza groups, researchers asked bow-and-arrow makers about their technologies, posing questions like: "Will an increase in draw weight, strength of pull, result in the arrow traveling faster, slower, or no change?" or "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?"

The questions provided the Hadza hunters the opportunity to demonstrate causal knowledge.

"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," study co-author Jacob Harris said in a press release.

"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," said Harris, a doctoral graduate student at Arizona State University.

Responses to the queries of Harris and his colleagues suggest Hadza hunters possess some causal knowledge, but that ability to innovate or maximize technological performance is at east partially constrained by cultural norms.

"Hadza bowyers construct powerful bows from local materials and use them to hunt a wide variety of prey. Over 95 percent 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," said co-author Brian Wood.

"Hadza men begin using bows at a very early age. Boys as young as three 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," said Wood, a researcher at UCLA.

But while Hadza hunters become more adept bow makers as they get older, researchers found no evidence that hunters acquire more causal knowledge as they age.

Older Hadza hunters possessed the same level of causal knowledge as younger Hadza hunters. Researchers also found no evidence that causal knowledge was associated with superior bow-and-arrow-making abilities, and the evolution of bow-and-arrow technology among Hadza hunters doesn't appear to be driven by expertise.

"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," said co-author Robert Boyd.

"It suggests that the human proclivity to rely upon cumulative culture rather than individual expertise likely has deep evolutionary roots," said Boyd, a professor of human evolution at Arizona State.

The latest findings suggest the cognitive niche hypothesis and the cultural niche hypothesis aren't necessarily mutually exclusive.

"In our study, we found evidence to suggest that a complete causal understanding is not necessary," Harris said. "But we also identified key aspects of Hadza projectile technology that were more likely to be associated with causal knowledge."

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