Fossils found in Kenya shed light on the origin of human hands.

For a long time, Paranthropus boisei , a hominid that inhabited the Earth from 2.6 million years ago to 1.3 million years ago, had been considered by experts as a relative of humans. Its robust jaw, large molars, and powerful masticatory muscles evidenced a diet as primitive as it was difficult to process, consisting of tough grasses and reeds that other species perhaps could not consume. In contrast, its hands, the limbs that in our species became a bridge between matter and idea, remained a mystery until today, when a study was published in the journal Nature to put an end to the mystery .

A team of paleoanthropologists , led by researcher Carrie Mongle of Stony Brook University (United States), has found the first definitively identified hand bones of Paranthropus boisei . The remains KNM-ER 101000, approximately 1.5 million years old, were found on the shores of Lake Turkana in northern Kenya between 2019 and 2021. This body part, described by specialists as "long sought," provides one of the most coveted pieces of the evolutionary puzzle and changes the picture of how this ancient human relative lived and moved.

Mongle, an evolutionary and phylogeneticist, says the discovery came about after one of the researchers noticed the shiny enamel of a molar on the surface of the soil. When the team began searching the area, they found a finger bone so large that at first they weren't sure it belonged to a hominid. "In a way, it was surprising how many aspects of this hand were similar to ours," she recalls.

The hand combines human features with those typical of African great apes . They found a long, robust thumb, short fingers, and a mobile pinky finger: proportions very similar to those of our own species, allowing for precision movements. “Since Paranthropus and Homo share an ancestor from about three and a half million years ago, comparing this hand with our own lineage also allows us to infer what the morphology of our last common ancestor might have been like,” Mongle explains.

A surprising hand

Researchers believe this powerful hand was not only primarily used for climbing, as previously assumed, but also for forcefully manipulating objects and food. Was the Homo genus unique in its ability to make tools? Until now, Paranthropus fossils have not been clearly associated with stone tools, but the remains reveal a mechanical ability to grasp, strike, or scrape objects, comparable to that of a person grasping a modern hammer, although researchers believe its precision was limited.

According to the authors, it could manipulate, but not carve with the finesse of Homo habilis . That is, P. boisei, discovered in 1959 by British anthropologist Mary Leakey in Tanzania , would have developed functional, rather than technological, skills. For Samar Syeda, a researcher at the American Museum of Natural History in New York, the human-like proportions suggest it had some capacity for gripping that would have allowed for the use of tools. However, "it primarily reflects locomotor use: a very strong type of grip, possibly related to climbing or holding on firmly."

According to this paleoanthropologist, it probably had the ability to use tools, even to make them. “ Tools have existed for at least 3.3 million years , and this hand dates back 1.5 million years.” But she adds that until tools are found “directly associated with a fossil hand,” it cannot be said with certainty.

A fossil that rewrites evolution

Regarding its lifestyle, paleontologist Almudena Estalrrich, a researcher at the National Museum of Natural Sciences , comments that the muscular marks on its hand indicate that it used it intensively, both for movement and for obtaining food. "For example, it could have used a stone to break large seeds," says this researcher, who was not involved in the discovery.

Adrián Pablos, a researcher at the National Center for Human Evolution , points out that this discovery changes the way we viewed this species and allows us to identify them as "more human and less other." This dispels the idea that their imposing jaw and teeth had relegated them to a secondary role in human evolution, as a less-than-skillful relative.

The hands of Paranthropus boisei add further evidence of the coexistence between this species and the genus Homo —to which modern humans belong—where footprints had already suggested a multiplicity of footprints in the same evolutionary environment. “A year ago, fossilized footprints were found that show the simultaneous presence of Paranthropus and Homo in the same space and time. The footprints were printed in volcanic ash,” Pablos points out.

KNM-ER 101000 demonstrates that dexterity was not the exclusive privilege of the Homo genus, but rather an evolutionary strategy shared by different species that, one and a half million years ago, explored the world with fingers capable of transforming their environment.

Estalrrich believes the significance of this discovery is evident: "For the first time, we have a postcranial remnant clearly associated with this species. This can help us identify other phalanges that had no owner." But he argues that the discovery also tells us a story of human evolution in constant flux: "What we previously took for granted is now being re-evaluated with new evidence and technologies."