This Time It's "Homo Naledi"
The news media might be heavily biased in favor of evolution, but at least they're predictable. Whenever a new hominin fossil is discovered, reporters eagerly seize the opportunity to evangelize for Darwin. Thus, when a new species, Homo naledi, was unveiled on September 10, 2015, it was no surprise that news outlets immediately buzzed about the discovery of a new "human ancestor."
CNN declared, "Homo naledi: New species of human ancestor discovered in South Africa." PBS hailed the discovery of a "Trove of fossils from a long lost human ancestor." The Daily Mail reported, "Scientists discover skull of new human ancestor Homo Naledi." NBC New York announced: "Scientists Discover Homo Naledi, Early Human Ancestor." And so on.
To be sure, the find is striking for its magnitude alone: hundreds of hominin bones were found in a cave near Johannesburg, South Africa. In a field where a single scrap of jaw gets everyone excited, this is a big deal.
But do we know that Homo naledi really is the "human ancestor" that so many news sources are now promoting? Dig into the details, and the answer comes up "No."
The main claim about Homo naledi is that it was a small-brained (compared to humans), upright-walking hominin, with a trunk similar to that of the apelike australopithecines, but with humanlike hands and feet. That's what the media has reported, but the details in the technical papers show that even some of those supposedly humanlike traits are unique:
• Regarding the hands, the technical papers note the "unique first metacarpal morphology"1; this and other sources indicate that naledi had long, curved fingers, suggesting that, unlike humans, it was well-suited for "climbing and suspension."2 According to a press statement from the researchers, "the H. naledi hand reveals a unique combination of anatomy that has not been found in any other human fossil before."3
• Likewise, a technical paper found that its foot "differs from modern humans in having more curved proximal pedal phalanges [i.e., toes], and features suggestive of a reduced medial longitudinal arch," giving it an overall "unique locomotor repertoire."4 In other words, naledi's foot shows that, again unlike humans, it was "likely comfortable climbing trees."5
• The technical papers similarly reveal "unique features in the femur and tibia" and a lower limb that "differs from those of all other known hominin."6
• Regarding the head, the main technical paper reporting the find states, "Cranial morphology of H. naledi is unique."7
In other words, overall, the species is highly unique. Lee Berger, the lead scientist who discovered the find, even admitted, "It doesn't look a lot like us."8 But the call to evangelize for Darwin is irresistible.
The discoverers of Homo naledi are calling it an "anatomical mosaic." That terminology raises a red flag. In the parlance of evolutionary biology, that usually means the fossil is a unique organism that doesn't fit easily into the standard evolutionary tree. As one technical paper concluded, "the H. naledi skeleton is a unique mosaic previously unknown in the human fossil record."9
Indeed, just four years ago, the hominin Australopithecus sediba—also discovered and promoted by Berger—was the transitional form du jure between the australopithecines and our own genus, Homo. Yet sediba is very different from naledi in some important ways, including the pelvis. If the same researchers now want to advocate Homo naledi as some new "transitional form," they must radically revise their evolutionary story.
Both sediba and naledi have been called a "human ancestor" in recent years, but evolutionarily speaking, both claims cannot be true. As one news outlet rightly acknowledged: "Each [sediba and naledi] has different sets of australopith-like and human-like traits that can't be easily reconciled on the same family tree."10
Another major challenge to claims for Homo naledi as a transitional form is the fact that the age of these newly reported fossils is currently completely unknown. The fossils could be very young (say, under 250,000 years old), and far removed from any hypothetical evolutionary transition between Australopithecus and Homo.
Homo naledi's promoters are suggesting it's between 2 and 3 million years old. But that dating isn't the result of a geological analysis, but is driven strictly by evolutionary considerations. We actually have very few bones from that time period and very little basis on which to document the supposed transition between the apelike australopithecines and the humanlike members of Homo.
Thus, at present, there's no geological evidence that naledi is from that time period and thus plugs some evolutionary "gap" in the fossil record. As Carol Ward, an anatomist at the University of Missouri, stated, "Without dates, the fossils reveal almost nothing about hominin evolution."11 Claims that it is a human ancestor are driven by hype, not evidence.
One or More? New or Known?
Yet another controversy over naledi is whether it represents a single species, or even a new species. The fossils' discoverers want the bones to encompass one single species, so they can declare a single hominin with a small head, an ape-like trunk, and humanlike hands and feet. But Jeffrey Schwartz, an anthropologist at the University of Pittsburgh, argued that the bones represent not one species but at least two, because of the differing shapes of various skulls found in the cave.12 If multiple species are present, the evolutionary model promoted by naledi's discoverers falls apart.
Others dispute whether naledi is a new species at all. University of California Berkeley paleoanthropologist Tim White was the focus of a scathing piece in his school's alumni magazine after he argued that naledi is nothing more than Homo erectus. According to the article, White sharply criticized the quality of Berger's excavation and analysis of the fossils:
White has cited other elements of the H. naledi saga that he finds troubling. The fossils come not from a single specimen, but from as many as 15 different individuals; it is therefore difficult to identify which bone came from which individual, and even whether they lived in the same period. . . . Photos taken of the find demonstrate to White that many of the fossils were not found in situ in the rocky matrix, but had been "very disturbed, perhaps by earlier cavers, in the geologically recent past."
"One tibia, for example, was white on one end, a clear indication it had been snapped off in the recent past," said White. "This (region's) complex is extensive and like Swiss cheese, and it's a favorite with spelunkers. You find beer cans next to fossils that are 3.5 million years old. So it's important not to jump to conclusions."
Further, the excavation itself seems inadequate to justify Berger's claims, White said. "It was about the size of a phone booth floor, roughly 80 x 80 cm and 20 cm deep," White said. "That's much smaller than you would expect for a discovery of this magnitude. Virtually all excavations related to important finds are much larger. With a typical excavation, you must establish a threshold that provides an understanding of the successive layers, that provides the means for comprehensive analysis and comparison with specimens from other sites."13
The article also noted that while few may share White's view that naledi is really just Homo erectus, many others in the field of paleoanthropology are skeptical of Berger's claims: "White is not alone in his uneasiness over H. naledi. Reviewers at top scientific journals also found the evidence for the new hominid species to be suspect. Berger and his team originally submitted multiple papers on H. naledi to the prestigious journal Nature, which rejected them." In the academic world, those are fighting words.
Buried or Lost?
Another dubious claim making the rounds in the media is that Homo naledi ritualistically buried its dead—a testimony to its supposedly human-like intellect. At best, it's not the case that this species buried its dead in any manner like we do. In fact, the bones weren't buried in the ground. Rather, it seems that the bodies were just tossed into the back crevice of a cave and left there to rot.
The cave's layout also means that if the members of this species did "bury" their dead, they had to crawl far back into a deep, dark cave, dragging a body through narrow crevices, in order to do so. That's difficult for any animal to do, and some have suggested that it would have required using torches. But this species had a small brain, not much larger than a chimp's, so the use of fire and burial by torchlight seems highly unlikely.
How, then, did these individuals end up in the back of the cave where they died? The most likely explanation is that, over the millennia, various unfortunate hominins found the cave a convenient place to flee to from such predators as lions or cheetahs. In desperation, they fled into the depths of the cave, where they got stuck or lost. Perhaps they were afraid to leave the cave. Perhaps it was too dark to find their way out. In any event, they died there in the back of the cave.
This explanation is more consistent with the evidence, so why do naledi's discoverers claim that the species ritualistically buried its dead? Simple: they want to have discovered a small-brained species exhibiting human-like behavior. Evolutionary considerations, not evidence, are again driving the conclusions.
Lastly, there are controversies about whether naledi even belongs in our own genus, Homo. Biological classification is a highly subjective enterprise, but given the species' small brain size and its australopithecine-like body, its placement within Homo has already proven controversial. Even Berger admitted to the New York Times, "There may be debate over the Homo designation," since "the species is quite different from anything else we have seen."14
Four years ago, the media were declaring Australopithecus sediba the newest human ancestor. But cooler heads eventually prevailed, and it was shown that sediba was from the wrong time period and had the wrong traits to be a link between humanlike members of the genus Homo and the apelike australopithecines.
What will become of Homo naledi remains to be seen. So far, however, its pathway resembles that of so many other hominin fossils whose "transitional" or "ancestral" status ultimately went belly-up. When evaluating media claims of a "human ancestor,"
a strong dose of healthy skepticism is warranted. •