A New Fossil Hominid, Homo naledi,
Raises More Questions Than It Answers
Copyright © 2015 Richard L. Currier
September of 2015, we learned that the human lineage has acquired yet another
ancestor. A team of scientists, headed by the paleontologists Lee Berger and
Paul Dirks, announced that the fossil remains of a new species of hominid,
which they christened “Homo naledi,” had been discovered in the Rising
Star Cave complex near Johannesburg, South Africa. But the discovery of this strange
new species raises more questions than it answers.
Unlike any other human ancestor, Homo naledi is a curious mixture of both very ancient and very modern characteristics.
Homo naledi’s finger bones are strongly curved, and such curved finger bones are typical of tree-dwelling species such as chimpanzees and orangutans. And, like “Lucy” and other early hominids, Homo naledi’s brain is only slightly larger than the brain of a chimpanzee. Moreover, its narrow shoulders and wide, flaring hips—also typical of tree-dwellers—are found only among the most ancient hominid species. The more highly evolved species from more recent eras had wide shoulders, narrow hips, straight finger bones, and much larger brains.
So why didn’t Berger and Dirks place their discovery in the genus Australopithecus, along with the other small-brained hominids such as Lucy? Why did they designate this species as belonging to the genus Homo, along with modern humans, Neanderthals, and Homo erectus, a large-brained human ancestor that used fire, made elegant stone tools, and may even have invented clothing and shelter?
The answer is that Homo naledi shares many anatomical characteristics with modern humans. In spite of its diminutive brain, the shape of its skull is very much like our own. Its teeth and jaws are small, like ours—far smaller than the jutting jaws of Australopithecus or the huge molars of Paranthropus, another early hominid. And although its finger bones are curved, Homo naledi’s hands are remarkably like ours, with humanlike proportions and a wrist structure that might well have been adapted for tool-making. And the anatomy of its legs and feet is strikingly modern.
Then there is the uniqueness of the site where the Homo naledi remains were found—a large chamber with an opening so small that only a special team of female archeologists were small enough to squeeze through the narrow opening and physically enter the site. Yet this chamber contains the largest single trove of early hominid fossils ever found—including hundreds of fossilized bones of individuals ranging in age from infancy to old age and the complete skeletons of at least fifteen individuals.
How did all these remains become deposited deep inside a cave complex through an opening only seven inches wide? The possibility that predators dragged them in there has been ruled out. They must have been deposited there by their fellow hominids. This raises the question of whether Homo naledi was deliberately disposing of their dead, yet such behavior has never occurred in all of human prehistory until the Neanderthals began burying their dead only a few thousand years before modern humans appeared in Europe.
And much to the frustration of everyone interested in human evolution, there is almost no way of judging how long ago Homo naledi actually lived.
Almost all other hominid fossils have been found within geological deposits that could be dated by the remains of other animals found there. But the virtually inaccessible chamber in this cave complex contains no other animal remains. Homo naledi could be more than three million years old or less than half a million years old. There is literally no way of knowing where Homo naledi should be located in the human family tree that paleontologists have so painstakingly constructed over the last fifty years.
So, is Homo naledi very ancient and primitive—as its ape-like characteristics would suggest—or is it relatively recent and more highly evolved, as its human-like features would indicate? Is it really a member of the genus Homo, or should it be assigned it to the genus Australopithecus? Should Homo naledi be considered an entirely new species? Or was it just an unusual population of one of the known hominids that paleontologists have been digging up from the African landscape for decades?
Stay tuned. The full story of human evolution is yet to be told.