Oldest flaked stone tools point to the repeated invention of stone tools

Oldest flaked stone tools point to the repeated invention of stone tools

stone tools
A large green artifact found in situ at the Bokol Dora site. Right: Image of the same artifact and a three dimensional model of the same artifact. Credit: David R. Braun

A new archaeological site discovered by an international and local team of scientists working in Ethiopia shows that the origins of stone tool production are older than 2.58 million years ago. Previously, the oldest evidence for systematic stone tool production and use was 2.58 to 2.55 million years ago.

Analysis by the researchers of early stone age sites, published this week in the Proceedings of the National Academy of Sciences, suggests that stone tools may have been invented many times in many ways before becoming an essential part of the human lineage.

The excavation site, known as Bokol Dora 1 or BD 1, is close to the 2013 discovery of the oldest fossil attributed to our genus Homo discovered at Ledi-Geraru in the Afar region of northeastern Ethiopia. The fossil, a jaw bone, dates to about 2.78 million years ago, some 200,000 years before the then oldest flaked stone tools. The Ledi-Geraru team has been working for the last five years to find out if there is a connection between the origins of our genus and the origins of systematic stone tool manufacture.

A significant step forward in this search was uncovered when Arizona State University geologist Christopher Campisano saw sharp-edged stone tools sticking out of the sediments on a steep, eroded slope.

Archaeologists from the Max Planck Institute, and the Ethiopian Authority for Research and the Conservation of Cultural Heritage as well as geologists from University of Algarve study the sediments at the Bokol Dora site. Stones were placed on the contact surface during the excavation to preserve the fragile stratigraphic contacts. Credit: Erin DiMaggio

"At first we found several artifacts lying on the surface, but we didn't know what sediments they were coming from," says Campisano. "But when I peered over the edge of a small cliff, I saw rocks sticking out from the mudstone face. I scaled up from the bottom using my rock hammer and found two nice stone tools starting to weather out."

It took several years to excavate through meters of sediments by hand before exposing an archaeological layer of animal bones and hundreds of small pieces of chipped stone representing the earliest evidence of our direct ancestors making and using stone knives. The site records a wealth of information about how and when humans began to use stone tools.

Preservation of the artifacts comes from originally being buried close to a water source.

"Looking at the sediments under a microscope, we could see that the site was exposed only for a very short time. These tools were dropped by early humans at the edge of a water source and then quickly buried. The site then stayed that way for millions of years," noted geoarchaeologist Vera Aldeias of the Interdisciplinary Center for Archaeology and Behavioral Evolution at the University of Algarve, Portugal.

Kaye Reed, who studies the site's ecology, is director of the Ledi-Geraru Research Project and a research associate with Arizona State University's Institute of Human Origins along with Campisano, notes that the animals found with these tools were similar to those found only a few kilometers away with the earliest Homo fossils.

Blade Engda of the University of Poitiers lifts an artifact from 2.6 million year old sediment exposing an imprint of the artifact on the ancient surface below. Credit: David R. Braun

"The early humans that made these stone tools lived in a totally different habitat than 'Lucy' did," says Reed. "Lucy" is the nickname for an older species of hominin known as Australopithecus afarensis, which was discovered at the site of Hadar, Ethiopia, about 45 kilometers southwest of the new BD 1 site. "The habitat changed from one of shrubland with occasional trees and riverine forests to open grasslands with few trees. Even the fossil giraffes were eating grass!"

In addition to dating a volcanic ash several meters below the site, project geologists analyzed the magnetic signature of the site's sediments. Over the Earth's history, its magnetic polarity has reversed at intervals that can be identified. Other earlier archaeological sites near the age of BD 1 are in "reversed" polarity sediments. The BD 1 site is in "normal" polarity sediments. The reversal from "normal" to "reversed" happened at about 2.58 million years ago, geologists knew that BD 1 was older than all the previously known sites.

The recent discovery of older hammering or "percussive" stone tools in Kenya dated to 3.3 million years ago, described as "Lomekwian," and butchered bones in Ethiopia shows the deep history of our ancestors making and using tools. However, recent discoveries of tools made by chimpanzees and monkeys have challenged "technological ape" ideas of human origins.

Archaeologists working at the BD 1 site wondered how their new stone tool discovery fit into this increasingly complex picture. What they found was that not only were these new tools the oldest artifacts yet ascribed to the "Oldowan," a technology originally named after finds from Olduvai Gorge in Tanzania, but also were distinct from tools made by chimpanzees, monkeys or even earlier human ancestors.

"We expected to see some indication of an evolution from the Lomekwian to these earliest Oldowan tools. Yet when we looked closely at the patterns, there was very little connection to what is known from older archaeological sites or to the tools modern primates are making," said Will Archer of the Max Planck Institute for Evolutionary Anthropology in Leipzig and the University of Cape Town.

The major differences appear to be the ability for our ancestors to systematically chip off smaller sharp-edged tools from larger nodules of stone. Chimpanzees and monkeys generally use tools for percussive activities, to hammer and bash food items like nuts and shellfish, which seems to have been the case with the 3.3 million year old Lomekwian tools as well.

Something changed by 2.6 million years ago, and our ancestors became more accurate and skilled at striking the edge of stones to make tools. The BD 1 artifacts captures this shift.

It appears that this shift in tool making occurred around the same time that our ancestor's teeth began to change. This can be seen in the Homo jaw from Ledi-Geraru. As our ancestors began to process food prior to eating using using stone tools, we start to see a reduction in the size of their teeth. Our technology and biology were intimately intertwined even as early as 2.6 million years ago.

The lack of clear connections with earlier stone tool technology suggests that tool use was invented multiple times in the past.

David Braun, an archaeologist with George Washington University and the lead author on the paper, noted, "Given that primate species throughout the world routinely use stone hammers to forage for new resources, it seems very possible that throughout Africa many different human ancestors found new ways of using stone artifacts to extract resources from their environment. If our hypothesis is correct then we would expect to find some type of continuity in artifact form after 2.6 million years ago, but not prior to this time period. We need to find more sites."

By 2.6 million years ago, there appears to be a long-term investment in tool use as part of the human condition.

Continued field investigations at the Ledi-Geraru project area are already producing more insights into the patterns of behavior in our earliest ancestors. New sites have already been found, and the Ledi-Geraru team will begin excavating them this year.

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This research was supported by the United States National Science Foundation and the John Templeton Foundation.

This research, "Earliest known Oldowan artifacts at >2.58 Ma from Ledi-Geraru, Ethiopia, highlight early technological diversity," is published in the Proceedings of the National Academy of Sciences.

 

Press release from the Arizona State University


human face hominins evolution

Need for social skills helped shape modern human face

Need for social skills helped shape modern human face

The modern human face is distinctively different to that of our near relatives and now researchers believe its evolution may have been partly driven by our need for good social skills

This is professor Paul O'Higgins from the University of York. Credit: University of York

The modern human face is distinctively different to that of our near relatives and now researchers believe its evolution may have been partly driven by our need for good social skills.

As large-brained, short-faced hominins, our faces are different from other, now extinct hominins (such as the Neanderthals) and our closest living relatives (bonobos and chimpanzees), but how and why did the modern human face evolve this way?

A new review published in Nature Ecology and Evolution and authored by a team of international experts, including researchers from the University of York, traces changes in the evolution of the face from the early African hominins to the appearance of modern human anatomy.

They conclude that social communication has been somewhat overlooked as a factor underlying the modern human facial form. Our faces should be seen as the result of a combination of biomechanical, physiological and social influences, the authors of the study say.

The researchers suggest that our faces evolved not only due to factors such as diet and climate, but possibly also to provide more opportunities for gesture and nonverbal communication - vital skills for establishing the large social networks which are believed to have helped Homo sapiens to survive.

"We can now use our faces to signal more than 20 different categories of emotion via the contraction or relaxation of muscles", says Paul O'Higgins, Professor of Anatomy at the Hull York Medical School and the Department of Archaeology at the University of York. "It's unlikely that our early human ancestors had the same facial dexterity as the overall shape of the face and the positions of the muscles were different."

human face hominins evolution
These are skulls of hominins over the last 4.4 million years. Credit: Rodrigo Lacruz

Instead of the pronounced brow ridge of other hominins, humans developed a smooth forehead with more visible, hairy eyebrows capable of a greater range of movement. This, alongside our faces becoming more slender, allows us to express a wide range of subtle emotions - including recognition and sympathy.

"We know that other factors such as diet, respiratory physiology and climate have contributed to the shape of the modern human face, but to interpret its evolution solely in terms of these factors would be an oversimplification," Professor O'Higgins adds.

The human face has been partly shaped by the mechanical demands of feeding and over the past 100,000 years our faces have been getting smaller as our developing ability to cook and process food led to a reduced need for chewing.

This facial shrinking process has become particularly marked since the agricultural revolution, as we switched from being hunter gatherers to agriculturalists and then to living in cities - lifestyles that led to increasingly pre-processed foods and less physical effort.

"Softer modern diets and industrialised societies may mean that the human face continues to decrease in size", says Professor O'Higgins. "There are limits on how much the human face can change however, for example breathing requires a sufficiently large nasal cavity."

"However, within these limits, the evolution of the human face is likely to continue as long as our species survives, migrates and encounters new environmental, social and cultural conditions."

 

 

The Evolutionary History of the Human Face is published in Nature Ecology and Evolution. The review was carried out in collaboration with colleagues from international institutions including the New York University College of Dentistry, the Natural History Museum, Arizona State University and Universidad Complutense de Madrid.

Press release from the University of York