1.4 Million-Year-Old Footprints Reveal Ancient Gender Roles in Kenya

Fossilized footprints unearthed near Lake Turkana in Kenya reveal that ancient hominin relatives, specifically Paranthropus boisei, may have practiced sex segregation for certain activities approximately 1.4 million years ago. A group of eight individuals, all identified as adult males, left their prints in moist ground, indicating they undertook a joint excursion without females or children.

The discovery, detailed in a recent study, provides a rare glimpse into the social structures of early hominin communities. The all-male group's presence suggests a complex social organization, potentially mirroring modern ape behavior where males form cooperative networks for territorial defense, patrolling, and hunting.

“The fact that eight, 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 Dr. Neil Roach, a researcher at Harvard University and co-author of the study. “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.”

Paranthropus boisei inhabited East Africa between 2.5 and 1.15 million years ago. While not a direct ancestor of modern humans, this species shared a common ancestor with species like Australopithecus afarensis before branching off and eventually becoming extinct. Before this trackway was discovered, most fossils of P. boisei consisted of skulls with large jaws and teeth, offering limited insight into their postcranial anatomy.

Insights from Fossilized Tracks

Previously, the robust bone structure of P. boisei led researchers to estimate males averaged about 4 feet 6 inches in height. However, advanced 2D and 3D imaging of the newly analyzed footprints, examining foot shape and locomotion patterns, revealed the individuals were significantly larger. The prints were comparable in size to those left by Homo erectus, a contemporary species that was thought to be considerably larger than P. boisei.

“The sizes of the footprints indicate human-like body sizes – up to 6ft tall and around 165lb,” stated Dr. Kevin Hatala, an associate researcher at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. “This was a surprising result, but we also have not known much about the anatomy of that species from the neck down, because most of their known fossils represent just their skulls and teeth.”

Dr. Hatala emphasized the unique value of fossil footprints: “Fossil footprints are really the only kind of data that can provide us with this direct window to social behaviour in an extinct species. This seems to indicate that this species lived in multi-male groups, with cooperation between adult males potentially being an important part of their social strategy.”

The research team utilized volcanic ash in the surrounding rock to date the trackway to approximately 1.43 million years ago during the Early Pleistocene epoch. In total, 21 footprints attributed to eight individuals were found alongside tracks from various animals, including hippos and antelopes.

The trackway was initially discovered by Dr. Kay Behrensmeyer of the Smithsonian's National Museum of Natural History around 50 years ago. It was later buried for preservation and has only recently been re-examined. Dr. Behrensmeyer highlighted the scientific significance of footprints: “The special thing about footprints scientifically is that they preserve an instant in time. They also allow people to relate to these fossils much more easily than an isolated piece of bone or jaw.”

Hundreds of hominin footprints have been discovered in the East Turkana lakeside region over recent decades, spanning more than 100,000 years. The finding that Paranthropus boisei was similar in size to Homo erectus raises new questions about the extinction of the former. “We can’t say how the two different hominins interacted on the mudflats, but we know they were both here at this time,” added Dr. Behrensmeyer.