Discoveries of new species tend to result from a combination of fortuitous luck and scientific nous. The discovery of Homo naledi certainly involved both.
In October, 2013, Rick Hunter and Steven tucker – both recreational cavers – stumbled across some human looking fossils in the Dinaledi cavern part of the Rising Star cave system. Initially fearing them to be the remains of fellow cavers they continued to see how far the cavern went back. On their return journey it became apparent that they may have stumbled upon some hominid fossils – previously, they had been told to be on the look out for fossils in this hominid fossil rich area, dubbed the Cradle of Humankind.
After pictures were sent to Professor Lee Berger an expedition party was assembled. Not more than two months after the discovery of these bones the excavation began…
In total the expedition team recovered an astonishing 1550 specimens – representing nearly every element in the skeleton – exclusively from one hominid species. It was at this point they noticed that this skeleton could not be attributed to any previously-known hominid species.
New discoveries of hominid tend to be rare so you can imagine the excitement and hype behind this finding.
The Dinaledi chamber
Located approximately 30 meters underground within the Rising Star cave system, the system lies within the Malmani dolomites, approximately 800 meters from the well-known site of Swartkrans in the Cradle of Humankind, South Africa.
Below is a schematic of the Dinaledi chamber illustrating the context and distribution of the fossils (from Dirks et al 2015).
“Homo naledi exhibits anatomical features shared with Austalopithecus, other features shared with Homo, with several features not otherwise known in any hominid species” – Lee Berger
The excavated fossils were from at least 15 individuals. Lee Berger described the Homo naledi as being similar in size and weight to a small modern human, with human-like hands and feet, though it shares anatomical features with Australopithecus.
The characterisation of H. naledi was based upon cranial, dental and post-cranial elements. The cranium, mandible and dentition are more consistent with the genus Homo but the cranial capacity, rib cage and scapulae are more like Australopithecus. The mandible is much more gracile than Australopethicus species.
Below is a picture of about 700 of the excavated bones. though it is important to note that the skeleton in this picture is a composite of elements that represent multiple individuals (From Berger et al. 2015).
Dinaledi hand 1 (Figure 1.) was found nearly complete in articulation. There is a combination of primitive and derived features not seen in the hand of any other Homo species. The mediolaterally narrow metacarpal 1 is different from any Homo while the curved phalanges differ from the Australopithecus’s.
With a similar hand morphology to Homo species Homo naledi was likely to have more enhanced object-manipulation capabilities than australopiths, the Homo-like leg would also suggest improved locomotion efficiencies with a striding gait (See this previous article on Homo locomotion for an explanation on hominid walking).
Although there is an incredible wealth of fossils yielding a massive amount of anatomical information, the Dinaledi deposit remains undated. This is important in being able to place this species within our lineage and maybe to help elucidate the ecological circumstances within which Homo arose and diversified. If these fossils were to date more than 2 million years ago than it would represent one of the earliest species represented by more than a single isolated fragment of bone in the Homo genus. Placing this species at the origin and diversification period of our genus (Berger et al. 2015).
A new species of homo was predictably met with both excitement and criticism in equal measure. While this deposit provides a wealth of knowledge,the homogenous nature of it is peculiar, in that it may represent deliberate disposal of the dead. The lack of dating of this deposit and the apparently human-like behaviour are the main sources of critique of this new species (Dirks et al. 2015) .
This research has perhaps asked more questions that it has answered. With the contrasting features, does this species represent the step between Homo and Australopethicus? Did this species lead the Homo genus on its way to us the Homo sapien? Or did it lead to another, now extinct, line of Homo?
Of course only time and further research will tell!
Here are the two articles published on Homo naledi (they’re free/open access), they both contain a great deal more information than my brief summary has given: