Nutcracker Man's Hand: What a 1.5-Million-Year-Old Fossil Reveals

For over sixty years, one question has hung over "Nutcracker Man." When Mary Leakey found the OH 5 cranium of Paranthropus boisei beside Oldowan stone tools in 1959, it was hailed as the oldest known toolmaker. That claim didn't last, and the debate over whether Paranthropus made or used tools has run ever since. The problem was a lack of evidence: no hand bones could be definitively attributed to the genus.

A new paper in Nature (Mongle et al., 2025) changes that.

The find

KNM-ER 101000, recovered at Koobi Fora on the shore of Lake Turkana, Kenya, is the first specimen to pair hand and foot bones with diagnostic P. boisei craniodental remains: large teeth with hyperthick enamel, small canines, and a sagittal crest. At slightly more than 1.5 million years old, it settles whose hand we're looking at. 

Human-like proportions, different mechanics

The thumb is long relative to the palm and fingers, just as in modern humans. That would have allowed P. boisei to bring thumb and fingertip pads together in precision grips, and to power-grasp objects. But the wrist and the base of the thumb retain primitive, ape-like features. The reorganized wrist architecture that helps modern humans and Neanderthals channel force from the thumb isn't present, so the authors conclude that precision pinching was probably less effective than in later Homo. Tool making and use in some capacity remains plausible, but the grip worked differently from ours.

An unexpectedly gorilla-like hand

Several features, especially in the thumb, the little-finger side of the palm, and the finger bones, converge on mountain gorillas. The obvious guess is climbing, but the evidence doesn't favor it. The finger bones lack the strong curvature that signals climbing and suspension, and the foot shows a strong commitment to bipedal walking. Gorilla climbing mechanics also seem to compensate for huge body size, and P. boisei was much smaller. However, KNM-ER 101000 preserved a large radial tuberosity (indicating a large biceps brachii muscle for strong forearm flexion) and powerful hand-grasping anatomy, which would have facilitated climbing performance. Even so, the authors emphasize that while a bipedal foot does not rule out occasional climbing, arboreal behavior was not the primary selective force shaping its anatomy.

The authors instead suggest the hand was built for forcefully processing food. Mountain gorillas use powerful, palm-dominated grips on tough vegetation, and P. boisei is reconstructed as eating a tough diet dominated by herbaceous, grass-like plants.

Bigger-picture implications

Because Homo and Paranthropus are sister groups, the new hand helps reconstruct their Last Common Ancestor (LCA). The authors' ancestral state reconstructions reveal that the LCA of Homo and Paranthropus possessed a robust thumb and fifth metacarpal suited for power grasping, whereas wrist modifications specialized for precision pinching evolved later in the Homo lineage. Furthermore, the strongly curved first metacarpal joint of KNM-ER 101000 weakens earlier arguments attributing the famous OH 7 hand fossils from Olduvai Gorge to Paranthropus.

Source: Mongle, C. S. et al. "New fossils reveal the hand of Paranthropus boisei." Nature 647, 944–951 (2025). https://doi.org/10.1038/s41586-025-09594-8