An international team of scientists, including one from the University of Washington, has announced the discovery of additional remains of a new human species, Homo naledi, in a series of caves northwest of Johannesburg, South Africa.
The find includes the remains of two adults and a child in the Lesedi Chamber of the Rising Star Cave system, expanding the fossil record originally reported from a different chamber of the cave in 2015.
Details of the latest discovery are published May 9 in two papers in eLife, along with another paper from the research team that pinpoints an age range of the original Rising Star fossils, which comprised 15 different individuals. Those remains of a primitive, small-brained human ancestor that scientists dubbed Homo naledi were found in Rising Star’s Dinaledi Chamber and are believed to be between 236,000 and 335,000 years old. This means that Homo naledi may have coexisted, for a period of time, with Homo sapiens, the species of modern humans.
“We can no longer assume that we know which species made tools, or even assume that it was modern humans that were the innovators of some of these critical technological and behavioral breakthroughs in the archaeological record of Africa,” said Professor Lee Berger of the University of the Witwatersrand in South Africa, who assembled the team that first explored the Rising Star system in 2013 and is an author on the latest papers. “If there is one other species out there that shared the world with ‘modern humans’ in Africa, it is very likely there are others. We just need to find them.”
The research involved 52 scientists from nearly three dozen institutions, led by the University of the Witwatersrand, James Cook University in Australia and the University of Wisconsin, Madison. The University of Washington’s Elen Feuerriegel, a postdoctoral researcher in the Department of Anthropology, was one of the members of the team that excavated both Dinaledi and Lesedi.
Researchers haven’t yet been able to date the fossils from the Lesedi Chamber, which include one of the most complete skeletons of an early human found to date. The excavation of that chamber, researchers believe, provides further evidence that this early human species deliberately disposed of its dead in these remote, hard-to-reach caves.
That hypothesis generated criticism when the Dinaledi discovery was first reported, with some scientists pointing to other potential causes and timelines for the deposition of the bones. The Rising Star team maintains that the lack of animal remains found at the site, and the absence of injury to or erosion of the human fossils, rules out predatory or natural causes of accumulation.
The Lesedi fossils also shed light on the physical capabilities of Homo naledi, said Feuerriegel. The finds so far indicate a species that walked upright and used its hands for complex grasping — like Homo sapiens — but also had an upper limb structure that was built for climbing, like more primitive humans.
“What we’re seeing is the importance of compromise in our own genus,” said Feuerriegel. “The fact that Homo naledi has a similar hand and wrist to Homo sapiens, but a brain one-third the size of ours, shows that they may not have needed as much brainpower to do complex things. The process of human evolution is more complicated than we thought.”
Further excavation of the cave system is planned, an undertaking that requires excavators who can squeeze through passages as narrow as 7 ½ inches and spend hours 100 feet underground. The original excavation team assembled for the Dinaledi Chamber in 2013 was made up of Feuerriegel and five other women, all of whom had paleoanthropology or archaeology backgrounds — and the caving skills critical to such an endeavor. Since then Feuerriegel, a caver who studies the upper limb structures of early humans, and other members of the team have returned for excavation of the Lesedi Chamber.
The new Lesedi fossils include the skull of an adult male that is more complete than one found in Dinaledi. The team has named the Lesedi skeleton Neo, and consider it more complete, too, than that of Lucy, the remains of an earlier species known as Australopithecus afarensis that were found in Ethiopia in 1974.
The specimens from Lesedi are similar to those from Dinaledi and are undoubtedly from the same species, said John Hawks, an associate professor of anthropology at the University of Wisconsin, Madison and an author on all three papers. Because determining the age of the Lesedi fossils could cause some damage to the Lesedi remains, researchers expect to begin that process after more fossils are collected. But team members believe that, based on the appearance and condition of the Lesedi fossils, that they fall within the same general time period as those of Dinaledi.
To establish an age of the Dinaledi fossils, scientists used a combination of techniques for both the bones and the surrounding sediments, including uranium series and electron spin resonance dating to examine teeth. Since other Australopithecus fossils have been found not far from the Rising Star Cave system, researchers had initially expected the Dinaledi fossils to be closer in age to those older ancestors — not from as recently as 236,000 to 335,000 years ago.
The age indicates that Homo naledi may have survived for as long as 2 million years alongside other species of early humans in Africa. In the period in which Homo naledi is believed to have lived, known as the Middle Pleistocene, it was previously thought that only Homo sapiens existed in Africa. That time is also characterized by the rise of what is considered “modern” human behavior in southern Africa, such as the use of complex tools and burial of the dead.
The Lesedi fossils will join those from the original Rising Star Cave expedition in a public display beginning May 25 at the Cradle of Humankind World Heritage Site near Johannesburg.