New wrist fossil work keeps knuckle-walking debate alive

knuckle-walking wrist – A new analysis of wristbone scans and more than 50 hominin wrist fossils finds shared wrist traits between humans and African apes that could relate to knuckle walking—but researchers stress the evidence doesn’t prove what our last common ancestor actually did

A familiar question in human evolution doesn’t die easily: did our shared ancestor with apes move with a gorilla-like knuckle walk, or did it keep its hands flatter, closer to how we think about modern chimps?

Because there’s no fossil of that last common ancestor, the answer has always depended on indirect clues. Now a new study, published Tuesday in the journal Proceedings of the Royal Society B: Biological Sciences, adds one more piece to the puzzle—by looking closely at the wrists themselves.

The researchers analyzed scans of wristbones from nonhuman primates. including gorillas. orangutans and chimpanzees. and paired those data with more than 50 hominin wristbone fossils. Their finding: humans and African apes share wrist traits that may be related to walking on knuckles. The authors stop short of turning that possibility into certainty. and they say more research is needed to explain what an older human species used those traits for.

The study focuses on a question that sounds simple but has a history of getting messy: the human-ape family tree doesn’t branch neatly in one direction. Scientists estimate it sprouted sometime between eight million and six million years ago. when an unknown ancestral species split into two lineages—nonhuman apes such as chimpanzees and bonobos. and hominins. upright-walking primates such as Neanderthals. Denisovans and anatomically modern humans.

With that kind of deep time—and no fossil left from the missing link—researchers have often turned to other routes. In this new work, the approach is two-pronged: fossils of extinct human “cousins” alongside the anatomy of living apes and humans.

Laura Hunter, who conducted the research while a Ph.D. student at the University of Chicago. argues that there are “traits which evolved in the common ancestor of humans and African apes” that. based on existing biomechanical research. could have been advantageous for knuckle walking. One of those features involves a “reorganization” of bones on the thumb side of the wrist in both knuckle-walking apes and humans.

The study’s title asks the key thing it can’t fully answer in one sweep: “Did Modern Human Carpal Morphology Evolve from Knuckle Walking Traits?” It was published online May 19, 2026, in Proceedings of the Royal Society B: Biological Sciences, Vol. 293.

A diagram in the paper shows seven of eight wristbones. The eighth bone—the pisiform—is pea-shaped in humans and rod-shaped in nonhuman apes, and it was excluded from the study for feasibility reasons.

For researchers watching the debate from the outside, the work looks like a step forward. Tracy Kivell. director of the department of human origins at the Max Planck Institute for Evolutionary Anthropology in Leipzig. Germany. called the study “excellent.” She wasn’t involved with the new research. In her view. previous efforts focused on specific wristbones. while this is “most comprehensive analysis of the wrist that we’ve seen yet.”.

But even strong datasets can’t erase the limits of the question. Hunter and her colleagues propose that the shared traits may have “stuck around” in the human lineage through evolutionary history—not necessarily for knuckle walking. but because they were also advantageous for object manipulation or sophisticated tool behaviors. a process biologists call “exaptation.”.

Kivell agrees the study is compelling, but points to why the answer still can’t be locked down. The analysis is focused on the wrist, and it doesn’t reveal much about other parts of the body that might have been involved in knuckle walking or movement broadly.

Then there’s the bigger problem: even if the wrists match, it doesn’t prove how the hands were used. Similarities between human and ape wrists could reflect knuckle walking. but they could also be tied to another wrist function such as climbing. or they could simply be remnants of how closely related our species are on the primate family tree.

“I think we won’t ever know this answer until we find fossils from that time period,” Kivell says.

Hunter makes a parallel point from the study’s framing. She stresses that the title is a question. not a statement—an invitation to weigh evidence rather than declare a conclusion. “There’s still a lot of work that definitely can be done to really figure out what exactly was happening with our ancestors. ” she says.

Her caution lands with particular weight because fossils only preserve so much. The species involved are extinct, so the behaviors that once shaped these bones may be permanently out of reach.

“If only we could go back in time and see what they were doing,” Hunter says.

Right now, the wristbones can’t offer that kind of certainty. What they do offer is a tighter connection between humans and African apes—enough to keep the knuckle-walking debate alive, and specific enough to narrow where future evidence will have to push.

human evolution knuckle walking apes wristbones carpal morphology hominin fossils African apes Proceedings of the Royal Society B