Last month in South Africa, scientists announced the discovery of a new group of early humans called Homo naledi. Now an analysis shows that this hominin had hands capable of both tree climbing and tool use, plus feet that were adapted for walking upright.
The remains of the extinct hominin were discovered in the Dinaledi Chamber of the Rising Star Cave system back in 2013. The fossils of at least 15 individuals—totaling 1,550 skeletal pieces—have since been excavated from the cave. In the ensuing paper, published in the science journal E-Life, the 47 co-authors proposed that the bones represent an entirely new species of the genus Homo. It’s way too early to tell if modern humans are descended from this species, but it’s clear we share a common ancestor.
Homo naledi bone table. (Photo credit: John Hawks_Wits University/CC)
H. naledi has a body and stature similar to Australopithecus—a small, extinct hominin that emerged some 4 million years ago in eastern Africa. But H. naledi also has a skull shape reminiscent of early Homo species. It probably weighed about 100 pounds, and stood nearly five feet tall. The remains have yet to be properly dated, but preliminary estimates place H. naledi at about 2.5 million to 3 million years ago. That said, some experts say more work is need to determine if all the remains belong to a single species, and until dating has been completed, the complete significance of this discovery cannot truly be known.
In an effort to paint a clear picture of the newly-discovered species, two separate papers released today in Nature describe the foot and hand of Homo naledi. Together, the studies strongly indicate that these ancient hominids were capable of both tree climbing and walking as their primary mode of movement—while also exhibiting the capacity for fine hand and finger movements.
Walking Upright Like Modern Humans
In the first paper, co-authored by CUNY anthropologist William Harcourt-Smith and colleagues, H. naledi’s foot was described from 107 distinct foot elements found in the Denaldi Chamber, including a well preserved adult right foot. Analysis shows that H. naledi and modern humans share much in common, including the capacity for standing and walking on two feet. In terms of differences, the ancient foot featured more curved toe bones, or proximal phalanges.
Digital reconstruction of the H. naledi foot (Image credit: W. E. H. Harcourt-Smith et al., 2015/Nature)
“Homo naledi feet are like yours and mine in so many ways, it is easier to just point out the subtle differences,” noted study co-author Jeremy DeSilva of Dartmouth College to Gizmodo. “The heel appears to be a bit less robust than ours, the arch is a tad flatter, and the toes are a bit more curved. Other than those relatively minor differences, Homo naledi had the most human-like foot of any known early humans except for Neanderthals. Based on the foot, and anatomies of the leg and knee, we can tell that Homo naledi walked a lot like humans do today.”
What’s more, the Naledi foot featured a strength and load capacity similar to modern humans, but distinct from chimpanzees—again, another clue that this species was, in the words of the researchers, “capable of efficient weight transfer through to a terrestrial substrate,” i.e. bipedalism.
The Dinaledi foot exhibits some of the most refined bi-pedal features ever seen in the hominin fossil record. As the researchers write in their study:
Although there are members of the genus Homo known with primitive feet and relatively small brains (H. floresiensis) and with derived feet and larger brains than H. naledi (for example, early H. erectus), H. naledi is the first known hominin with this combination of such derived feet and legs with a small brain size.
What’s more, and like Lucy— the famous Australopithecus afarensis specimen—H. naledi’s pelvis was more outward flaring, allowing for more leverage in walking.
Hands for Climbing and Tool Using
The hand of H. naledi was analyzed by lead author Tracey Kivell and colleagues. Her team looked at nearly 150 different points, including a nearly complete adult right hand (it was missing a wrist bone). The researchers say the hand exhibits features never seen before in a human fossil.
Digital reconstruction of the H. naledi foot (Image credit: W. E. H. Harcourt-Smith et al., 2015/Nature)
Analysis of the wrist bones and thumb indicate that these ancient humans featured a powerful grip and were capable of precise manual manipulation required for the use of stone tools.
The paper’s abstract summarizes the researcher’s findings rather nicely:
This hand reveals a long, robust thumb and [an evolved] wrist morphology that is shared with Neandertals and modern humans, and considered adaptive for intensified manual manipulation. However, the finger bones are longer and more curved than in most australopiths, indicating frequent use of the hand during life for strong grasping during locomotor climbing and suspension. These markedly curved digits in combination with an otherwise human-like wrist and palm indicate a significant degree of climbing, despite the derived nature of many aspects of the hand and other regions of the postcranial skeleton in H. naledi.
This mix of seemingly ancient and modern features demonstrates that H. naledi’s hand was specialized for both complex tool-use activities and climbing.
“The tool-using features of the H. naledi hand in combination with its small brain size has interesting implications for what cognitive requirements might be needed to make and use tools, and, depending on the age of these fossils, who might have made the stone tools that we find in South Africa,” noted Kivell in a release.
Missing Link?
These findings are quite intriguing, so it’s natural to wonder if H. naledi represents some kind of “missing link” in the fossil record. DeSilva says we need to refrain from using such language.
“The ‘missing link’ concept is based on an old and misguided idea that humans evolved from apes as we know them today and the resulting expectation that fossils would reveal a half-human, half-ape ancestor,” he told Gizmodo. “But, that is not how evolution works! Apes have evolved, too.”
DeSilva says that, instead of evolving from chimpanzees, we know that humans and chimpanzees share a common ancestor that was neither human nor chimpanzee.
“We now have thousands of fossils of early human ancestors and extinct relatives, and this growing human fossil record reveals species like Homo naledi that have different combinations of ape-like and human-like anatomies, but I’d never call Homo naledi half-human and half-ape,” he says. “Our evolutionary history has been much more complicated, and interesting, than that.”
Read the studies at Nature: “The hand of Homo naledi” & “The foot of Homo naledi.”