Twenty-one ancient footprints discovered in northern Kenya, dating back over 1.4 million years, suggest that Paranthropus boisei, an extinct relative of modern humans, may have traveled in all-male groups. Researchers analyzed the footprints, preserved in sediment along the edge of an ancient lake, to determine they belonged to P. boisei, a species nicknamed 'Nutcracker Man' for its large jaws and molars.
Scientists believe the tracks capture a single moment when eight individuals walked together along the lakeshore. The size and arrangement of the footprints indicate they were made by multiple adult males, hinting at a complex social structure. Researchers propose these males may have traveled together for protection in a dangerous environment, despite potentially competing with each other for mates.
"The fact that eight, mostly adult male P. boisei individuals seemingly travelled together as a group, without females or children, hints at a complex social structure in this species," said co-author Neil Roach of Harvard University. "They may have lived in large groups, where males competed for mates, but also tolerated each other at times for safety in a dangerous environment."
The discovery was made in the Koobi Fora Formation on the eastern edge of Lake Turkana, a region known for its rich archaeological and fossil sites. The sediment layers have preserved crucial evidence of early human evolution over the past two million years.
Detailed 2D and 3D imaging was used to analyze the footprints, which were then compared to tracks made by modern humans and other ancient hominins. The analysis confirmed the tracks belonged to P. boisei, a species that lived alongside early humans like Homo erectus but belonged to a separate, extinct branch of the human family tree.
The size of the footprints also surprised researchers, suggesting P. boisei individuals could have been significantly larger than previously estimated. Lead author Kevin Hatala of Chatham University stated that the footprints indicate human-like body sizes, with some individuals possibly standing up to 6 feet (1.8 meters) tall and weighing around 75 kilograms (165 pounds). This challenges earlier beliefs that P. boisei was much smaller than contemporary Homo erectus.
This new research adds to hundreds of ancient hominin footprints documented from multiple sites around Lake Turkana, spanning over 100,000 years. Each discovery contributes to a growing understanding of human evolution.
The researchers hypothesize that the lakeside environment, abundant with resources like papyrus and shellfish, may have drawn P. boisei. The team plans to continue excavations in the area to uncover more about the lives of these ancient relatives.
Recent findings in 2024 also identified footprints from both P. bocei and Homo erectus at Lake Turkana, providing the first direct evidence that these distinct human relatives inhabited the same locations simultaneously and potentially interacted with one another.