It all started with a tip that there might be bones in a South African cave.
When paleoanthropologist Lee Berger of the University of Witswatersrand in Johannesburg began to follow this lead from amateur cave explorers in 2013, he had no way of knowing his team would discover a never-before-seen species of human that could revolutionize our evolutionary tree. The new species was granted the name Homo naledi, meaning "star" in the local language of Sesotho, as an homage to the cave in which the bones were retrieved.
Two papers detailing this astounding discovery were published in the open-access journal, eLife.
One of the most profound aspects of the find is the entirety of the collection. The bones likely came from about 18 individuals, ranging in age from young infants to those who had lived to old age.
"With almost every bone in the body represented multiple times, Homo naledi is already practically the best-known fossil member of our lineage," Berger explained in a statement.
Fully grown, H. naledi stood about 4.5 to 5 feet tall, and likely had a slender stature weighing about 100 pounds. Its brain was small, roughly the size of an orange.
There is evidence that the bodies were complete when they were brought back in the cave and that this practice occurred over an extended period of time. This suggests that H. naledi had a special resting place for their dead, as opposed to some catastrophe that killed a large number of individuals in that location at once. This insight into the social behavior of the species is incredible.
There is also much that can be learned from the morphology of the bones themselves, particularly of the hands and feet.
"The hands suggest tool-using capabilities," co-author Tracy Kivell from the University of Kent added in the statement. "Surprisingly, H. naledi has extremely curved fingers, more curved than almost any other species of early hominin, which clearly demonstrates climbing capabilities."
The shape of the foot is more similar to a modern human than to a chimpanzee — our closest living ancestor. This indicates that H. naledi likely walked upright, an important factor in making sense of this newly discovered species.
But the shape of some of the bones isn't very straightforward, leading to some confusion about what their lives were really like. While they were capable of walking upright, they also show signs of being avid climbers as well, traits that are muddled between early members Homo and Australopithecus.
"Overall, Homo naledi looks like one of the most primitive members of our genus, but it also has some surprisingly human-like features, enough to warrant placing it in the genus Homo," senior author John Hawks from University of Wisconsin, Madison explained in the release.
While there is still much to learn about this incredible discovery, one glaring question remains: how old is Homo naledi?
In order to fully understand H. naledi's significance, researchers have much more to learn about this ancient hominin and its true place in the timeline of human evolution.
Most notably, there isn't an exact timeline for when H. naledi lived on Earth. Based on physical features of the bones, the scientists were able to work out roughly when it existed, but nothing has been stated definitively yet. The bones were not found near the bones of another species that would provide context, and three different methods used to date the bones have been unsuccessful.
Fortunately, there will be no shortage of opportunities to analyze this new species. In addition to the treasure trove of bones that have already been excavated from the cave, the researchers wholeheartedly believe that there is much more waiting to be revealed.
"This chamber has not given up all of its secrets," Berger continued. "There are potentially hundreds if not thousands of remains of H. naledi still down there."
Many of the researchers working on this project are in the infancy of their careers. Rather than merely providing lip service to the fact that the next generation of scientists need good opportunities, Berger selected his team purposefully. Though it was impossible to know ahead of time what they would find in the cave, these young scientists were able to cut their teeth and become part of a truly extraordinary discovery.