Homo naledi, the latest hominin species to be added to the human family tree, still stirs quite the excitement in the scientific community almost four years after archaeologists dug up its bones.
The new species was discovered in South Africa in 2013 and got its name from the Rising Star cave system where its fossils were unearthed — the word naledi means "star" in the SeSotho language.
Because of its remarkable characteristics, our ancient relative made it to the 2016 To 10 New Species list, a selection of the most impressive newly discovered species published every year by the College of Environmental Science and Forestry (ESF) at the State University of New York.
But the quest to find more answers about this new human ancestor is still ongoing, as researchers believe they've only just scratched the surface and expect to find more fossilized remains — possibly hundreds or even thousands — waiting to be brought to light so they can tell their tale.
The Discovery Of Homo Naledi
At the time, scientists from the University of the Witwatersrand (Wits) in Johannesburg, led by Prof. Lee Berger, uncovered around 1,500 fossil fragments belonging to at least 15 different individuals.
All the ancient bones were found stacked in the Dinaledi Chamber ("Chamber of Stars" in SeSotho) within the Rising Star cave system — part of the Cradle of Humankind World Heritage Site.
Since then, archaeologists explored another chamber in the cave system, where they stumbled upon the remains of at least three new Homo naledi specimens, including a perfectly preserved skull.
How Old Is Our Human Ancestor?
Trying to ascertain the age of Homo naledi has proved a daunting task. Because the fossils were so ancient, using DNA recovery methods to establish the period they belonged to was virtually impossible.
To get to the bottom of this, Wits' paleoanthropologist Francis Thackeray devised a mathematical technique to measure the size of the hominin's skull. The results initially suggested Homo naledi may be two million years old.
However, the fossils unearthed in the Dinaledi Chamber exhibited both primitive and modern features, boggling the scientific community.
The hominin's skull pointed to a small brain, only 500 cubic centimeters in volume, similar to Australopithecus. But the rest of its skeleton was strangely mismatched, showing modern features that resembled the more evolved hominins in the Homo genus.
This led researchers to believe Homo naledi was right on the cusp of the transition between Australopithecans and our more recent ancestors, making it a good candidate for the title of earliest Homo species.
Living Alongside Homo Sapiens
However, a new method of fossil testing revealed Homo naledi was shockingly younger than previously thought.
The scientific community was flabbergasted earlier this week when a new study announced the fossils dugout during the Rising Star Cave expedition were no more than 236,000 to 335,000 years old.
The new discovery, which used multiple techniques to date the bones such as electron spin resonance dating, Uranium-series dating on the fossilized teeth, and Uranium-Thorium dating of the sediments in the cave, suggests Homo naledi coexisted with Homo Sapiens.
If this theory holds true, Homo naledi would join Neanderthals, Homo floresiensis (more popularly known as the Indonesian "hobbit"), and Denisovans to become the fourth known hominin species to have existed alongside modern-day humans.
What Did Homo Naledi Look Like?
The most striking characteristic of our ancient ancestor is the mosaic of its physical features.
Even though its skull was remarkably different from the Homo sapiens, accounting for a brain size of only around a third of the modern humans, the rest of its body had a relatively lanky, human-like skeletal structure.
"Anatomical features of this new hominin found in South Africa are a mixture of those of Australopithecus with other Homo species, combined with several features not known in any hominin species," edescribes ESF.
According to their analysis, our ancestor was "similar in size and weight to a modern human" and, despite the size of its skull, shared a series of physical traits with the other Homo species, including "locomotion, manipulation, and mastication."
Homo naledi had extraordinarily human-like feet and long legs, which suggest the hominin had the capability of walking upright and was actually accustomed to hiking long distances. However, the skeletal structure of its upper body was more primitive.
Just like its skull, Homo naledi's shoulders, pelvis, and ribcage had more in common with hominins than modern humans. Its shoulders were poised for hanging from trees and its fingers were curved, suited for curling around branches.
Amazing Facts About Our Ancient Relative's Behavior
The anatomy of its torso and feet indicates Homo naledi could easily climb trees. Our ancestor had ape-like curved toes, as well as longer finger bones than other hominins, which helped it grasp branches while climbing and being suspended from trees.
At the same time, its wrists and thumbs closely resembled those of Neanderthals and modern humans, suggesting Homo naledi had the ability to make and use tools.
This was surprising given the species small brain and led researchers to rethink the cognitive requirements needed for using tools.
But what makes Homo naledi truly special are the cultural practices the species seems to have followed. Our ancient relative may have done something previously thought to be unique to modern humans: burying their dead.
Sign Of A Highly Evolved Intelligence
The two separate discoveries of multiple fossils in different cave chambers of the Rising Star site led researchers to believe the hominins were intentionally storing the bodies of their dead into remote caches, signaling 'ritualized behavior.'
Although just a hypothesis, it would explain why the archaeologists found so many skeletal remains in such a dark and inaccessible spot.
The condition of the fossils suggests the individuals died of natural causes — the bones bear no clues to indicate they had fallen prey to carnivores or that their bodies were scavenged. They also seem to have been carried into the chamber by fellow hominins, at different moments in time.
What is more, among the fossils unearthed in the Dinaledi Chamber archaeologists found only a handful of bones belonging to other animals, such as mice and birds. This shows the remote space was not easily accessible and would have attracted few accidental visitors.
"We explored every alternative scenario, including mass death, an unknown carnivore, water transport from another location, or accidental death in a death trap, among others. In examining every other option, we were left with intentional body disposal by Homo naledi as the most plausible scenario," said Prof. Berger.
Researchers point out this is a sign of a highly evolved intelligence similar to the Homo sapiens.