For at least 2.6 million years, humans and our ancestors have made stone tools by chopping off flakes of material to produce sharp edges. We consider stone tools to be very rudimentary technology, but producing a useful tool without wasting much stone requires skill and knowledge. Therefore, archaeologists tend to use the complexity of stone tools as a way to measure the cognitive abilities of early humans and the complexity of their cultures and social interactions.
But because the same tool-making techniques weren’t common everywhere early humans lived, it’s hard to really compare how stone tool technology evolved over the entire 2.6-million-year history of stone tool-making or across the ages. wide geographic distribution of early humans. To do that, you need to find a common factor.
So a team led by anthropologist Željko Režek of the Max Planck Institute for Evolutionary Anthropology decided to investigate whether the length of the sharp, working edge of rock flakes changed over time in proportion to the size of the flakes. A longer, sharp edge is more efficient and requires more control and skill to create, so Režek and his colleagues reasoned that it would be a good indicator of how well early humans understood the stone working process and how well they used that knowledge. shared each other. other.
A quick lesson in stone knocking
When you try to knock a sharp flake off a piece of rock, the size of the flake and the length of the edge depends on how and where you hit the stone core.
“Stone artifacts vary enormously in complexity, but the physics of stone carving means that the most fundamental part of the process of their creation — the loosening of flocs — is similar, whether you’re producing a single large, sharp flake to create a animal or touches the finish on a microlithic weapon component,” wrote University of Bordeaux archaeologist Natasha Reynolds, commenting on Režek’s study.
One of the most important factors is the thickness of the flake where it starts (called the platform depth). Another is the angle between the surface hit to create the flake and the surface of the stone core from which the flake breaks off (called the outer platform angle). A larger outside corner of the platform will create a flake with a long edge in proportion to its size. But doing it right takes planning, skill and knowledge.
“Controlling these two variables when creating a flake requires the ability to direct force to a precise location for a given platform angle,” Režek and his team wrote. “This is a skill that is unique to humans.” And that, they say, means that the length of a flake’s working edge can reveal something about the skill of its makers. That, in turn, could provide clues as to how hominid cultures evolved and passed on new skills over the past 2.5 million years.
So Režek and his colleagues measured the edges of more than 19,000 rock flakes from 81 groups of artifacts from locations in Africa, Southwest Asia and Western Europe, spanning a stretch of human history from gay habilis 2.6 million years ago to modern humans 12,000 years ago. Those sites contain artifacts from at least five hominin species: H. habilis, H. erectus, H. heidelbergensisNeanderthals and modern humans.
Edges are getting longer, but also more diverse
During the Pleistocene the mean length of the working edges increased relative to the floc size. Early Pleistocene stone flakes, made by H. habilis and H. erectus before about 1 million years ago, it had the shortest working edges in the study. However, after about 1 million years ago, the flake edges started to lengthen, and it seems that H. erectusfollowed by H. heidelbergensis and Neanderthals, learned how to control platform depth and exterior platform angle to get sharper edges relative to the size of their flakes.
That trend continued with modern humans, but at the same time, the length of the edges also started to vary more from site to site. Modern humans who lived about 50,000 years ago produced the flakes with both the longest and shortest sharp edges for their size. It seemed like people had learned how to make more efficient flakes, but they don’t always put that knowledge to work.
But that variation may actually be a sign of technological advancement for early humans.
Being able to get a flake with a longer edge from a single stroke is a very efficient use of stone, giving you an advantage when you are short on resources or when you have to carry a stone a long distance to work or to use . But there are other ways to make sharp edges – for example, the small, sharp Upper Paleolithic blades in the air-raid shelter of the Abri Pataud cave in France have very short edges, but clearly show refined, efficient craftsmanship.
Meanwhile, toolmakers with the same precision and skill that enabled the production of longer cutting edges could vary their cutting edge length for techniques such as Levallois or for making short blades. Comparing the length of sharp flake edges still provides a good insight into developing the control and skill needed to do it.
And sometimes a sharper edge wasn’t the answer. “The production and use of projectile tools has been critical in some contexts, while in others simple thick flakes may have been a selective advantage,” Režek and his colleagues wrote.
The ability to adapt the technique to the context is actually quite advanced, and that may be what accounts for the increase in variation between flake edges over time. Looking at all these locations in general, it seems that human culture has gotten better at producing sharp rock flakes over time, even as hominins apparently learned to vary the results as needed.
More questions to answer
Režek’s findings generally support what archaeologists have understood for years about the general trend toward skill and complexity in early human technology, but it is one of the first studies comparing large numbers of artifacts over so much time and distance. The rim’s length gives archaeologists a standardized, concrete way to look at the big picture of human cultural evolution, which has been one of the greatest challenges for Paleolithic archaeologists to date.
If archaeologists can find ways to apply that method to other aspects of stone tool making or in other geographic areas, it could help them address some of the big questions about the development of human culture and cognition. .
“It would be interesting to know how these trends hold up as more data is included, for example from early Neanderthals with systematic leaf production or more of the varied assemblages associated with anatomically modern humans in North Africa,” Reynolds wrote. “It would also be interesting to consider Holocene knapd lithic assemblages, including those from Australia and America.”
Nature2017. DOI: 10.1038/s41559-018-0488-4 (About DOIs).