Exploring the Origin of a Species

Only a year and a half after discovering fossil remains of a new hominin species, scientists—among them Bryn Mawr College Visiting Professor of Anthropology Caroline VanSickle—have come to a startling conclusion about the species they dubbed Homo naledi.

A relative of humans, the small-brained hominin lived in Africa during the early Middle Stone Age, some 335 to 236 thousand years ago, and was perhaps a next-door neighbor of early Homo sapiens.

The original find was made in the newly discovered Rising Star cave system, which would prove to be one of Africa’s richest fossil sites. Scientists were baffled by the tiny-brained creature that had apelike shoulders but, in some parts, bore a striking resemblance to humans.

At the time, VanSickle joined an international team examining thousands of fossils to figure out what they were, how the parts fit together, how many individuals were represented, and what species they were.

“My focus was on the pelvis, which in hominins tells us how a species walked, what their posture might have been like, and how they may have given birth,” VanSickle explains. “The Homo naledi pelvic remains are a collection of small fragments of incomplete bones, so many of these questions are still unanswered.

“In many ways, the pelvis of Homo naledi most closely resembles that of the three-million-year-old hominin Lucy (Australopithecus afarensis), which is strange since the rest of the skeleton does not particularly resemble Lucy, and now we know that H. naledi lived much more recently than Lucy.”

This May, when scientists announced their conclusions about H. naledi’s age, they also revealed the discovery of additional remains—of a child and an adult male—unearthed in Lesedi, a newly explored chamber of the Rising Star complex.

Among the new material the excavation team found was a hip fragment. Researchers sent a 3-D scan of that fragment to VanSickle, who collaborated with the South Africa team to compare it to those from the original site. “The Lesedi fragment is the most complete immature hip fossil we have from this species so it can potentially tell us something about how the species grew,” she explains. 

Today, she continues to lead a research team with expertise in torso reconstruction, hominin growth and development, and the hominin pelvis. Together, the team is comparing the remains from each cave site to each other—and to that of other hominin species.

“In 2015, I thought this species' mosaic anatomy was the most interesting part of the story: the small brain, Homo erectus-like head shape, australopith-like torso and pelvis, human-like foot, and gibbon-like shoulder shouldn’t belong in one body, and yet we had clear evidence that they all went together,” says VanSickle.

“Now, I find it incredible that this unusual skeleton belongs to a species that lived so recently that it overlaps with the earliest members of our own species.”