Scientists dispute 'new' species discovery

Deep inside a cave 30 miles from Johannesburg, South Africa, a tight crevasse guards the passageway to what was, until recently, the grave of at least 15 human-like individuals. Their bones and teeth—more than 1,500 fragments in all—lay in a heap in the bottom of a pitch-black chamber for ages, until two skinny spelunkers with flashlights squeezed into the earth deep enough to find them.

Now those bones are in the hands of scientists who say they belong to a new species of prehumans, with a mix of features typically associated with modern man or fossils belonging to Australopithecina, a group of creatures considered to be ancestors to humans on the evolutionary tree. The scientists, who announced their findings on Thursday, have named the new species Homo naledi, after the local word for “star.”

Depending on their age, the bones could throw into contention some widely accepted views of human evolution—such as the idea that only modern humans were smart enough to methodically bury their dead. The discovery is unusual in that so many fossils were found at a single dig site.

“With every bone in the body represented multiple times, it is already practically the best-known fossil member of our lineage,” said paleoanthropologist Lee Berger in a conference call with reporters. Berger, a University of Witwatersrand professor and National Geographic explorer-in-residence, led the effort to excavate and study the fossils.

But the discovery has already stirred up controversy among researchers, some of whom are unconvinced the fossils represent a new species of hominin—an evolutionary label that includes modern humans and their ancestors.

The definition of “species” is itself somewhat arbitrary. Christoph Zollikofer, an anthropologist at the University of Zurich, doesn’t believe the new fossils have enough “new and unique” features to justify calling them a new species.

“The fossil ensemble fits very well into what is already known as ‘early Homo erectus,’” he told me by email.

There’s no question the fossils, discovered deep inside Rising Star cave, are intriguing. Although the cave had been explored many times before, the bones were unknown to researchers until two spelunkers discovered, by chance, the narrow passage leading to them. The crevasse was so tight (8 inches in some places) Berger could not enter the fossil chamber himself: Instead he advertised on Facebook for slender scientists willing to carry out the claustrophobic excavation. Six women ultimately got the job. Berger and other team members ended up watching the excavation work by video link outside the cave.

Berger and the team that studied the fossils say the Rising Star hominins had brains as small as a gorilla’s, less than half the size of most people’s brains today. The males stood about 5 feet tall and weighed 100 pounds, on average. They said the creatures had curved fingers useful for climbing, but had feet similar to humans and suitable for long-distance walking. Their teeth had an odd combination of modern and “primitive” characteristics. Altogether, the team said, the fossils exhibited a “mosaic” of atypical features.

“Whenever you hear the word ‘mosaic’ in evolutionary lingo, what that means is this species does not fit very well into our preferred phylogenic scheme,” said Casey Luskin, a research coordinator for the Center for Science and Culture at the Discovery Institute, a think tank in Seattle that promotes intelligent design. “There’s a lot of people that are disputing that this could be a human ancestor.”

The scientists admit they don’t know the fossils’ age: The bones were not in a sediment layer that could be dated, and the researchers have not yet performed radiocarbon dating, which will damage the bones. Based on their interpretation of the evolutionary tree, they believe the fossils to be 2.5 million years old or more. That would potentially make them—to the delight of some evolutionary biologists—a transitional form between ancestral australopiths and the more modern Homo genus.

Berger admitted, though, that the fossils might be only tens of thousands of years old. Dating efforts are ongoing.

But some scientists dispute Berger’s contention that all 1,500 bones came from the same species.

“Why do all belong to the same species? Because they were found in the same cave,” wrote University of Pittsburgh anthropologist Jeffrey Schwartz in a commentary. “But, the published images tell a different story.” Schwartz said the skull fragments had different shapes, suggesting they came from different species and might not even belong in the Homo genus.

The bones came from at least 15 males and females, including infants and elderly. One big mystery is how these individuals ended up so deep in a hard-to-reach cavern: There are no teeth marks suggesting animals dragged the bones there, and no rubble suggesting a flood deposited them there. Berger’s hypothesis is that they were intentionally buried in the cave as part of a ritualistic interment.

But Luskin said the small size of Homo naledi’s brain has made many researchers skeptical it was intelligent enough to deposit its dead deep inside an unlit cave. He instead suggested the individuals might have hid in the cave from predators and then died there.

The Homo naledi fossils have elicited differing viewpoints even among researchers who accept a creationist paradigm for human origins.

“I think the case is very strong that these fossils are not just of the genus Homo, but are actually fully human (meaning they are descendants of Adam and Eve),” said Kurt Wise, director of the Center for Creation Research at Truett-McConnell College. Wise noted that early humans dispersed after the biblical Tower of Babel incident would have lived in isolated populations and developed highly distinct traits.

But Fazale Rana, a researcher at Reasons to Believe, a Christian apologetics organization, thinks the fossils represent a distinct species.

“I just simply see these as creatures that God created that existed and went extinct,” he said. “I don’t think you can in any way, shape, or form say that this is some kind of variation of a human being.”

Rana added that disruptive fossils are an ongoing occurrence in evolutionary paleoanthropology: “This is another instance of a new hominid find that basically is forcing everyone to go back and rewrite their human evolutionary story.”

The fossil discovery is featured in the upcoming October issue of National Geographic magazine and in the open-access journal eLife, in two papers.