Scientists have announced the discovery of 15 partial skeletons belonging to what is thought to be a previously unknown species of ancient human. The remains were recovered from the Rising Star cave in South Africa by a team female scientist-climbers specially selected to fit through a narrow, vertical shaft (just 8 inches wide at points) and reach the chamber of fossils below.

More than 1,500 fragments of bones were discovered in total — the largest single paleoanthropological find of its type in Africa — with the researchers, led by Professor Lee Berger, designating the species naledi, meaning "star" in the local Sesotho language. Berger and his colleagues have suggested that the remains could belong to one of the earliest members of the genus Homo (to which modern humans belong), although some scientists are more skeptical.

The holotype specimen of Homo naledi, including cranium and mandible. (John Hawks)

Homo naledi is not being described as a "missing link" (a term which poorly reflects the complex, patchwork history of bipedal primates and early humans), but will certainly shed more light on humanity's evolution. The 15 partial, but well-preserved skeletons include both males and females, and old as well as young individuals. "We are going to know everything about this species," Berger told BBC News. "We are going to know when its children were weaned, when they were born, how they developed, the speed at which they developed, the difference between males and females at every developmental stage from infancy, to childhood to teens to how they aged and how they died."

According to descriptions published in the journal eLife, the bones themselves show a blend of primitive and modern anatomical traits, with a small skull suggesting a brain approximately the same size as a gorilla's (a third the size of modern human's), and humanlike hands and feet. Some experts have suggested that the curved fingers resemble those of Homo habilis (thought to be among the first toolmakers), while the modern-looking feet and relatively long legs would suit a creature that could walk upright over long distances. It's traits like these that have led scientists to place naledi in the genus Homo, rather than the extinct genus Australopithecus, to which the famous Lucy specimen belongs. The average Homo naledi was probably between 4.5 and 5 feet tall and weighed under 100 pounds.

The front and back view of a hand. (Peter Schmid)

There is still a lot that isn't known about the bones, including, importantly, their age. Berger and his team have suggested the remains could be up to 3 million years old — with the species evolving near the beginning of the Homo genus — but they could also be more modern. Tests like carbon dating will allow accurate dating of the fossils, but these will destroy the samples and will have to wait until the bones have been studied more thoroughly. Until this information is available, some scientists are skeptical about the find's exact significance.

"If they are as old as 2 million years, then they might be early South African versions of Homo erectus, a species already known from that region," anthropologist William Jungers told The Guardian. "If much more recent, they could be a relic species that persisted in isolation. In other words, they are more curiosities than game-changers for now."

The question of how the skeletons arrived in the cave is also unanswered. There's no evidence in the cave of habitation, and the bones show no signs of a violent death. Some experts suggest the individuals became trapped in the cave or died when it flooded, but Berger and his team claim the evidence points to early burial rites — a startling suggestion given the relatively primitive development of naledi. "We are going to have to contemplate some very deep things about what it is to be human," Berger told BBC News. "Have we been wrong all along about this kind of behavior that we thought was unique to modern humans? Did we inherit that behavior from deep time and is it something that (the earliest humans) have always been able to do?"