Homo rudolfensis: Finally shown to be a separate species?

Homo habilis is the earliest member of our genus, living from 2.3-1.4 million years ago.  It was the first species to use stone tools and the first to really look more human than ape, with a face that didn’t stick out anywhere near as far as chimps’ or Australopthecines’. However it isn’t directly related to us. Instead it was a sister species which ultimately died out, like the neanderthals or Paranthropines. This means that the early history of our genus is complex since the human lineage must exist somewhere, along with any other branches H. habilis was related to.

One example of this complexity is Homo rudolfensis, a hominin nobody was quite sure existed. Living ~1.9 million years ago it is known from only a single skull which shares many similarities with Homo habilis. Although several potential H. rudolfensis fossils have been found over the years, few can definitely be placed within the skull’s family. This lack of data, combined with the similarities between the skull and H. habilis has resulted in many debates over whether the H. rudolfensis finds are an entirely new species or simply an example of variation within H. habilis.

Handily 3 new fossils from Kenya may shed some light on the issue by clarifying the anatomy (and thus taxonomy) of Homo rudolfensis. All three come from Koobi Fora, a famous African site which also yielded the original H. rudolfensis skull. The excavation was led by a member of the Leaky family which has been studying human evolution in Africa for 3 generations. They’re practically an evolutionary anthropology institution, uncovering the first evidence of the Oldowan industry, the first Paranthropine and Turkana boy, amongst many other things.

Homo rudolfensis (right) and Homo habilis (left)

The first fossil died ~1.9 million years ago and is a juvenile, about as developed as a 13/14 year old modern human. However, the life history of these hominins was shorter so this individual was likely younger than comparable modern humans, probably around 8 years old. Although most teeth were missing, there were sufficient to provide an estimate of the age range for this fossil. Like the teeth, most of the bones themselves are also missing and all that’s left is the upper jaw and a portion of the face.

Juvenile fossils are weaker and thus rare so there aren’t that many specimens this new one can be compared with. The researchers estimated what it would look like as an adult to circumvent this problem, although that does introduce a potential margin for error. Their predictions place this specimen within the genus Homo, having a flatter “human” like face than Australopithecines. The fossil itself also attests to this conclusion, being more similar to Homo finds, particularly the few juvenile ones available. Most interestingly, it contains the same features which sets the original H. rudolfensis skull apart from H. habilis.

The juvenile fossil

The second fossil is a lower jaw, one side of which is particularly well preserved. From this well preserved side they were able to work out what the other side looked at, removing essentially all errors that any damage would cause. The find itself dates to between 1.87 and 1.78 mya, making it younger than the juvenile. As such, questions are immediately raised over whether it belongs to the same species as the juvenile. Particularly given that there are a few differences between the two specimens.

It certainly comes from the genus Homo. Most of the teeth are preserved in the jaw which are smaller than Paranthropine teeth and fall either within or slightly below the range for early Homo, confirming its designation as a member of that genus. Is it part of the same group as the other finds?  It turns out that despite the aforementioned differences, this fossil does appear to be most similar to the juvenile described above, which in turn is most similar to the original H. rudolfensis skull. The final fossil is a lower jaw fragment dating to ~1.9 mya. Like the second fossil, it is most similar to the juvenile and so is also probably a member of H. rudolfensis.

The second and third (fragment in the bottom right) fossils.

Most news outlets have claimed that these fossils are the discovery of some new species. However, as I mentioned, the original H. rudolfensis cranium is nearly 40 years old! This find can hardly be categorised as a new species. A more accurate headline would be “New fossils confirm suspected species exists.” Although the truth is less snappy I do not believe that justifies ignoring it. But before I go writing letters to newspapers demanding corrections, do these fossils in fact confirm H. rudolfensis was a real, distinct species? Although they can clearly be grouped with the original cranium, does that indeed lend credence to placing this group outside of Homo habilis?

These fossils show that there was a population of individuals with a unique anatomy and that the original skull was not just a funky looking individual. This certainly lends credence to the idea that H. rudolfensis was a distinct species rather than an example of individual variation. But of course, “population” does not equal “species” and so the fact there was a population of these unique creatures does not prove they were a different species. Whilst a point in favour of H. rudolfensis being distinct, it is not conclusive proof. That must come from the anatomy, from figuring out whether these creatures are different enough to be defined as a different species. Ultimately the number of examples of anatomy isn’t as important as the anatomy itself.

Of course, that shouldn’t diminish the importance of these fossils. Although these finds might not be as crucial as newspapers say they are (one even reporting this “rewrites the story of human evolution“), what we label a species is not that important. We now know that there was definite, population wide variation within early Homo and that the story of our genus’s genesis (try saying that after a few pints) is even more complex than the single cranium suggested. It might not “rewrite” the story, but it is certainly editing a chapter.

Meave G. Leakey,, Fred Spoor,, M. Christopher Dean,, Craig S. Feibel,, Susan C. Antón,, & Christopher Kiarie, Louise N. Leakey (2012). New fossils from Koobi Fora in northern Kenya confirm taxonomic diversity in early Homo Nature (488), 201-204 DOI: 10.1038/nature11322

EvoAnth joke:
“What’s Santa’s favourite Hominin?

Homo rudolfensis