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African dig uncovers bone tools that offer insights on early human life

Jackson Njau's fascination with human origins started as a curious teen growing up a few hours from one of the most famous archaeological sites in the world. Now a pioneering paleoanthropologist at Indiana University Bloomington, his research is reshaping knowledge of our early human ancestors and their interactions with prehistoric environments.

Njau is an associate professor in the College of Arts and Sciences' Department of Earth and Atmospheric Sciences and a faculty affiliate of the Hamilton Lugar School of Global and International Studies' African Studies Program. His work seeks to understand the relationship between paleoenvironments and the development of early human ancestors, or hominins.

Through the lens of anthropological perspectives, his work centers on the study of animal remains and their geological contexts from archaeological sites.

For two decades he's conducted research at the Olduvai Gorge in Tanzania, a UNESCO World Heritage site hailed as the "Cradle of Humankind." The site was made famous by Louis and Mary Leakey through their groundbreaking discovery of early human fossils.

Njau grew up 250 miles east of the Olduvai Gorge in Moshi, Tanzania, near Mount Kilimanjaro, the tallest mountain in Africa. As a teen, he was fascinated by the Leakeys' discoveries.

"Dr. Louis Leakey was very famous in Tanzania," Njau said. "He was a very charismatic guy who spoke Swahili on the radio programs about the significance of Olduvai. I was fascinated mainly by his pictures of hominin fossils featured in local newspapers and National Geographic magazines, and often wondered, 'How do you find a fossil? Where do you look? How can you tell if it's a rock or bone, and how old it is?'"

While studying archaeology as an undergraduate, he attended an international field school in Koobi Fora, Kenya, which was co-founded by a Harvard professor and renowned paleoanthropologist Richard Leakey, Mary and Louis Leakey's son.

"It was a great connection point in the world of paleoanthropology," Njau said. "After my long research at Olduvai, now I bring my students there to try to give them the same experience I had."

Njau's work was among the first to explore the stresses of carnivore predation on prehistoric humans by examining bones embedded in the earth from millions of years ago. In a striking discovery at Olduvai Gorge, he found the presence of crocodilian bite marks on the bones of early humans.

This finding led to the discovery of a previously unknown species of crocodile, Crocodylus anthropophagus, meaning the "man-eating crocodile."

"This evidence shows that crocodiles played a crucial role in the advancement of early human cognition, especially since many of the tooth-marked hominin bones belonged to young individuals, suggesting that many were still learning, often fatally, the life of nature," Njau said.

Recently, a project co-directed by Njau and Ignacio de la Torre of the Spanish National Research Council published a study in the journal Nature, describing the discovery of the world's oldest bone tools at Olduvai, dated 1.5 million years old.

Although human ancestors began crafting stone tools as early as 3.3 million years ago, the systematic manufacture of bone tools was previously thought to be a relatively recent innovation. Before this discovery, the oldest known bone tools were found in Eurasia and are estimated to be only 250,000 to 500,000 years old.

The bones were from limbs of large mammals, most commonly elephants and hippopotamuses, and were shaped and sharpened by rocks. The evidence offers valuable insight into the technological shift driven by the need to exploit new sources of raw materials. This suggests that they had a knowledge of animal anatomy, bone properties and which bones made the best tools, and they were able to transfer their knapping skills from stone to bone, displaying clear evidence of complex cognition.

This invention marked a crucial technological transition between Oldowan and Acheulean industries between 1.7 million and 1.4 million years ago. Previously understood only through stone tools, this cultural shift is now being reexamined through the emerging evidence of bone tools.

Surprise discovery

The astounding discovery of bone tools associated with thousands of stone tools and animal fossils started when torrents carved through Olduvai Gorge during the 2010 rainy season, exposing buried secrets. Njau had been on the ground, eyes locked on the freshly exposed outcrops. A few hominin teeth he found at a dig site prompted years of excavation from 2015 to 2022.

According to Njau, this site was likely a seasonal hippopotamus pool that dried up during the dry seasons, stranding animals that Homo erectus then scavenged and butchered using stone artifacts and hefty bone implements.

"Olduvai Gorge is known for the breakthrough discoveries that unfold the history of our ancestors layer by layer," Njau said. "Our discovery is another stunning finding that pushes back the origin of bone tools another 1 million years, rewriting the timeline of our ancient ingenuity."

Understanding the past, anticipating the future

By studying hominin adaptations, researchers can address global contemporary issues, Njau said. Olduvai Gorge offers a unique opportunity to examine records of past climates and environments. How these factors influenced hominin lives can inform our response to current global issues and help us anticipate the future.

This line of scientific inquiry is among the goals of the Stone Age Institute, where Njau is a research scientist. The institute is co-directed by IU emeriti professors Nicholas Toth and Kathy Schick.

Recently, Njau, Toth and Schick assembled over two dozen researchers from around the world, including IU students and faculty members, to investigate the impact of Earth's dynamics on hominin origins. This study illuminates the complex interplay between earth processes and hominin adaptations, extending the paleoenvironmental record of Olduvai to an unprecedented level, Njau said.