Homo naledi’s Powerful Hand Up Close
After the excitement of Homo naledi’s discovery and extraction from deep in a narrow cave in South Africa, and the implication that these non-humans may have intentionally carried their dead deep into the earth, we are left with the bones themselves, what they tell us about these creatures, and what new questions they inspire.
These sketches and notes come from interviews and conversations during both the 2013 Rising Star Expedition and the 2014 workshop where established experts and early-career scientists came together to analyze the 1,550 fossil pieces.
The Hand
Now maybe everyone just had rock-climbing on the brain since that’s what it took to recover the bones of naledi from the cave.
But that said, during its excavation, as the various finger bones were extracted and laid out, it was clear that Homo naledi could have given Alex Honnold a run (or a climb) for his money.
The first clue to the strength of these hands was the size and shape of the thumb. The bones themselves are longer in proportion to the other fingers than ours are, and the contours of the bones show they had very large muscles attached.
Other apes have long palms and fingers, with smaller thumbs kept out of the way down by the wrist. Their hands are enormously powerful, with an average female chimp having the grip strength of an NFL linebacker, and they can obviously climb with ease and dexterity.
Human thumbs on the other hand (so to speak) are more like equal players with the other fingers. They are similar in size and range of motion, which is great for manipulating objects with precision, but the reduced size of the fingers and palms makes them weaker, and the prominent thumb is prone to painful snags if we try to swing through the trees.
Naledi seems to have the best of both worlds. Like humans and australopithecines such as Lucy and sediba (Lee Berger’s other big find), the thumb is opposable, but uniquely, it is also huge and muscular. That’s intriguing, but alone it’s not evidence that the creature was a good climber. For that there is another clue.
We might tend to think of a skeleton as basically a steel superstructure our muscles are draped over, but our bones are living, growing, and changing based on use just as much as the rest of us. For climbers of all sorts, the suspension of weight and the repeated strong gripping applies stresses that induce the digits of the fingers to curve. This is visible in x-rays of athletes, and it’s visible in the bones of naledi’s fingers as they rest in your hand.
Since the naledi find has not yet been dated, we do not know if the creatures lived among dense forest or open savanna, and so whether they would have spent much time in and among trees. Regardless of the groundcover though, the ground itself would have been largely the same: undulating hills with rocky outcroppings and caves everywhere.
Climbing could certainly have been an advantage, and naledi would have had to rely on strong hands to do it. Its feet wouldn’t have been much help. They were too much like ours.