Discovery pushes stone-tool use by early humans back 800,000 years

Two Arizona State University researchers conducting zooarchaeological and archaeometric analyses of four fossilized animal bone fragments found by the Dikika Research Project in northeastern Ethiopia – within walking distance of the discovery of the hominin skeleton “Lucy” (Australopithecus afarensis) – confirm that unusual marks on the bones were inflicted by stone tools. Their conclusion weighs in on findings reported in the Aug. 12 journal Nature, that A. afarensis used sharp-edged stones and a strong striking force to cleave flesh and marrow from large-sized animal carcasses some 3.4 million years ago.

That evidence pushes back the origins of technology – the use of stone tools – and carnivory by some 800,000 years, from 2.6 Myr to 3.4, explained Curtis Marean, a paleoanthropologist at ASU’s Institute of Human Origins and one of the world’s leading experts in the study of animal bones from archaeological sites.

Marean, a professor in the School of Human Evolution and Social Change in ASU’s College of Liberal Arts and Sciences, is a member of the international team made up of experts in paleoanthropology, archeology, geology, paleontology and materials science who reported the findings in the Nature article “Evidence for stone-tool-assisted consumption of animal tissues before 3.39 million years ago at Dikika, Ethiopia.”

The zooarchaeological analysis of the bone fragments, which included a femur shaft from an animal the size of a goat and a rib fragment from a much larger animal the size of a cow, was conducted at Arizona State University. Using a standard binocular microscope in ASU’s zooarchaeology laboratory, Marean was able to provide evidence that sharp-edged stones and a strong striking force were used to remove flesh and marrow from the bones of large-sized animal carcasses.

To further determine that the markings were not modern, he turned to Hamdallah Béarat, a senior research scientist at ASU’s School for Engineering of Matter, Transport and Energy.

“To confirm that the cutmarks on the bones are ‘old’ and verify that they were induced by stone tools, I used the Environmental Cell Scanning Electron Microscope (E-SEM) and the attached Energy Dispersive X-ray Spectrometry (EDX) in ASU’s LeRoy Eyring Center for Solid State Science,” said Béarat, who has degrees in chemistry, archaeometry, material science and engineering.

The E-SEM was used because it has a chamber and stage that can accommodate large bone fragments, Béarat explained.

“And, since the bone material is an insulator and these precious bone samples cannot be coated with a conducting film, such as gold or carbon, this E-SEM allows us to run the analysis in the H2O-vapor mode and thus avoid charging effects, while still using a high accelerating voltage (15-25kV),” Béarat said.

“Hamdallah is an expert in materials research and keenly interested in archaeology,” noted Marean. “He had the great idea to do X-ray mapping of the surfaces of the bone to see whether minerals that passed from the marks to the surface of the bone were fossilized.”

The geologist on the team, Jonathan Wynn, from the University of South Florida, relied on documented dated volcanic deposits in the Dikika area to estimate the date of the marked bones to 3.4 million years ago.

“This discovery dramatically shifts the known timeframe of a game-changing behavior for our ancestors,” said paleoanthropologist Zeresenay “Zeray” Alemseged, director of the Dikika project and director of anthropology at the California Academy of Sciences.

No hominin remains were found with the animal bone fragments that were uncovered 200 meters away from the site where Alemseged and a team discovered “Selam” (Lucy’s baby) in 2000. Lucy was discovered in 1974 a few miles north, near Hadar, by Donald Johanson, the world renowned ASU paleoanthropologist.

“There is no question that the announcement of stone tool use at 3.4 million years ago will unleash a flurry of controversy and genuine disbelief among some scholars,” said Johanson. “However, I believe the team has presented a convincing case of stone tool use during Lucy’s time. These unexpected results may well generate a new understanding of early hominid behavior and will prompt a reexamination of the tens of thousands of animal bones already collected from this time period at Hadar, Lucy’s home, and other sites in Kenya and Tanzania.

“Very often it is breakthroughs such as this that stimulate new and expanded research strategies that promise to significantly enlarge our understanding of human origins,” Johanson said.

Lead author of the Nature article Shannon McPherron observed: “Now, when we imagine Lucy walking around the east African landscape looking for food, we can for the first time imagine her doing so with a stone tool in her hand.” McPherron is an archeologist with the Dikika project and research scientist at the Max Planck Institute in Leipzig, Germany. He and Alemseged led the Dikika fieldwork.

The last place early humans – like Lucy – wanted to be on the African landscape was in a competitive dangerous situation next to an animal carcass, noted Marean.

Yet, “these marks are unusual compared to other butchery marks I have seen,” he said. “They show a lot of force, a lot of heavy action.”

Marean framed the research findings as “a spectacular and exciting discovery pertaining to early human evolution.” But, while the evidence shows the Australopithecines at Dikika were using sharp-edged stones to crack and strip meat from the bones, it is impossible to tell from the marks alone whether these early hominins were making their tools and carrying them, or simply finding naturally sharp rocks.

Many questions remain about the use of stone tools by human ancestors and the introduction of meat into their diet.

“The subtle implication is that in this instance, it was not hunted but scavenged meat and marrow, since the really large animal was almost certainly outside the ability of hominins to kill. This could be a key tipping point in the origins of human uniqueness,” Marean said. “One of the big steps in human evolution is when males and females pair-bond, and males provided females with meat. This result may suggest this is happening at this early stage in human origins.”

Other co-authors of the Nature paper include paleontologists Denné Reed, University of Texas, Austin; Denis Geraads, Centre National de la Recherche Scientifique, Paris; and René Bobe, University of Georgia.

The interdisciplinary nature of the team exemplifies what collaboration between social sciences and physical sciences can produce, noted ASU’s Béarat.

“I believe that, in the coming few decades, major archaeological discoveries are to be expected in the laboratory rather than in the field,” he said, advocating for more archaeometric studies, which are like forensic investigations. “In both cases, the scientist is investigating a process or an act. In this case from Dikika, our role was to confirm, using physical/engineering methods, that the act of cutting the bones was old and thus corresponded to our remote hominin ancestor.”