New Human Species Identified from Kenya Fossils
by Pallab Ghosh
Science correspondent

8 August 2012
from BBC Website

Researchers studying fossils from northern Kenya have identified a new species of human that lived two million years ago.

The discoveries suggests that at least three distinct species of humans co-existed in Africa. The research adds to a growing body of evidence that runs counter to the popular perception that there was a linear evolution from early primates to modern humans.

The research has been published in the journal Nature.
 

A new species of human:

One of several co-existing in Africa two million years ago

Anthropologists have discovered three human fossils that are between 1.78 and 1.95 million years old.

The specimens are of a face and two jawbones with teeth.

The finds back the view that a skull found in 1972 is of a separate species of human, known as Homo rudolfensis. The skull was markedly different to any others from that time. It had a relatively large brain and long flat face.

But for 40 years the skull was the only example of the creature and so it was impossible to say for sure whether the individual was an unusual specimen or a member of a new species.

With the discovery of the three new fossils researchers can say with more certainty that H. rudolfensis really was a separate type of human that existed around two million years ago alongside other species of humans.

For a long time the oldest known human ancestor was thought to be a primitive species, dating back 1.8 million years ago called Homo erectus. They had small heads, prominent brows and stood upright.

But 50 years ago, researchers discovered an even older and more primitive species of human called Homo habilis that may have coexisted with H. erectus. Now it seems H. rudolfensis was around too and raises the distinct possibility that many other species of human also existed at the time.

This find is the latest in a growing body of evidence that challenges the view that our species evolved in a smooth linear progression from our primate ancestors.
 

The human lineage
 

Instead, according to Dr Meave Leakey of the Turkana Basin Institute in Nairobi, who led the research the find shows that there was a diversity early on in the evolution of our species.

"Our past was a diverse past," she told BBC News, "our species was evolving in the same way that other species of animals evolved. There was nothing unique about us until we began to make sophisticated stone tools."

In other groups of animals many different species evolve, each with new traits, such as plumage, or webbed feet. If the new trait is better suited to the environment then the new species thrives, if not it becomes extinct.

According to Professor Chris Stringer of the Natural History Museum in London, fossil evidence is increasingly suggesting that human evolution followed the same pattern.

"Humans seem to have been evolving in different ways in different regions. It was almost as if nature was developing different human prototypes with different attributes, only one of which, an ancestor of our species, was ultimately successful in evolutionary terms," he said.

According to Dr Leakey, the growing body of evidence to suggest that humans evolved in the same way as other animals shows that "evolution really does work".

"It leads to amazing adaptations and amazing species and we are one of them," she said.

The New Koobi Fora Early Homo Fossils

by Adam Van Arsdale
August 9, 2012

from  Wellesley Website
 

UPDATE
For some additional takes, check out Erin Wayman’s piece at Hominid Hunting (Smithsonian) and Zachary Cofran’s great discussion of these new fossils alongside the material from Malapa, South Africa, at Lawnchair Anthropology.
 

Meave Leakey, Fred Spoor and colleagues have a new article in Nature featuring some wonderful new fossils from Northern Kenya, dating to between 1.75 and 2.0 million years of age.

This is a critical time period in human evolutionary history, as it corresponds to the early evolution of our genus, Homo. The article has gotten a lot of attention, with stories in the New York Times, two related commentaries in Nature, and I am sure numerous other stories elsewhere.

I am not sure if the actual article is behind a firewall or not, but here is the abstract:

Since its discovery in 1972 (ref. 1), the cranium KNM-ER 1470 has been at the centre of the debate over the number of species of early Homo present in the early Pleistocene epoch(2) of eastern Africa.

 

KNM-ER 1470 stands out among other specimens attributed to early Homo because of its larger size, and its flat and subnasally orthognathic face with anteriorly placed maxillary zygomatic roots(3).

 

This singular morphology and the incomplete preservation of the fossil have led to different views as to whether KNM-ER 1470 can be accommodated within a single species of early Homo that is highly variable because of sexual, geographical and temporal factors(4, 5, 6, 7, 8, 9), or whether it provides evidence of species diversity marked by differences in cranial size and facial or masticatory adaptation(3, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20).

 

Here we report on three newly discovered fossils, aged between 1.78 and 1.95 million years (Myr) old, that clarify the anatomy and taxonomic status of KNM-ER 1470. KNM-ER 62000, a well-preserved face of a late juvenile hominin, closely resembles KNM-ER 1470 but is notably smaller.

 

It preserves previously unknown morphology, including moderately sized, mesiodistally long postcanine teeth. The nearly complete mandible KNM-ER 60000 and mandibular fragment KNM-ER 62003 have a dental arcade that is short anteroposteriorly and flat across the front, with small incisors; these features are consistent with the arcade morphology of KNM-ER 1470 and KNM-ER 62000.

 

The new fossils confirm the presence of two contemporary species of early Homo, in addition to Homo erectus, in the early Pleistocene of eastern Africa.

Indeed, these are wonderful new fossils, particularly the KNM-ER 62000 lower face and KNM-ER 60000 mandible.

Writing for Scientific American, Kate Wong has a nice commentary on the story that includes several quotes from me, which I thought I could clarify and expand on a bit.

So, Leakey, Spoor and colleagues (as well as just about all of the other commentators I have seen) feel these new fossils provide additional evidence for multiple, concurrent species of Homo at the Pliocene-Pleistocene boundary (~1.6-2.0 million years ago). I suggest that might not be the case.

What makes me so crazy?

To explain, it helps to have a little historical perspective on the “problem” of early Homo.

The current arguments about early Homo can be viewed, in some ways, as dating back to the discovery of fossil material from Olduvai Gorge by Mary and Louis Leakey back in the 1960s.

When the original Olduvai material was discovered it showed a combination of characters that appeared intermediate between already known South African Australopiths (A. africanus, in particular) and already known Asian (and to a less extent, African) Homo erectus such as those from China and Java.

Philip Tobias, controversially, gave them the designation Homo habilis and placed them as a transitional species. Over time a lot more fossils from this 1.5-2.0 time period were discovered, and rather than clarifying the set of relationships, these new fossils simply added more and more variation to the picture.

This is particularly true for the huge number of fossils uncovered by researchers in the Turkana/Omo basin region of Northern Kenya and Southern Ethiopia (e.g. KNM ER-1470, KNM WT-15000, KNM ER-3733, KNM ER-992, KNM ER-1813, KNM ER-1805 and many many more).

As a result, Homo habilis, which was already rather poorly defined on the basis of features that don’t preserve well (hand morphology), are highly variable (cranial capacity, dentition size), or non-morphological (tool use), began to be viewed as representing multiple taxa.

Instead of representing a transitional lineage, it came to be viewed more and more as a radiation, and the primary question of interest became how many species (Habilis?, Rudolfensis?, Ergaster?, Erectus?) and which one ultimately led to us. I had the opportunity to view most of these fossils in Nairobi in 2004 while doing my dissertation research.

Indeed, while I was there, Meave Leakey and Fred Spoor were doing work on earlier published materials for Ileret, and were very kind and gracious to me in talking about their work and my own dissertation research.

One thing that made my view different was that I was not looking at the fossils from the perspective of someone who was accustomed to seeing the fossils from an African perspective. I had already been working at the site of Dmanisi for several years and had just finished a sustained period of work on the Dmanisi fossil assemblage.

Dmanisi, although 2000 miles away in Georgia, is positioned smack in the middle of this critical time sequence (~1.76 Ma), but comes from a single, rapidly deposited locality, with fantastic preservation of multiple individuals and partial skeletons. And what is interesting about Dmanisi is the tremendous morphological variation present in an isolated sample.

At Dmanisi we see an echo of the larger pattern of variation in the East African record, but on a smaller, more interpretable scale.

For example, consider the following image (approximate scale, the Dmanisi 2600 mandible has been horizontally reflected to allow for the comparison of its better preserved side):

Prior to the publication of KNM ER-60000, the Dmanisi 2600 mandible was truly exceptional in many respects relative to other mandibles assigned to early Homo.

In particular, the size of its corpus and height of its ramus stood out.

This new specimen from Kenya, dating from a similar time, is the best match we have yet for its features. And yet it is being linked to a fossil, KNM ER-62000, that has notable affinities (despite a significant difference in size) with KNM ER-1470, a fossil that prior to this publication also appeared somewhat morphologically exceptional relative to its peers.

The authors also note similarities between the new lower face (KNM ER-62000) and the Dmanisi 2700 individual.

So in some ways, these fossils seem to be filling in a gap between earlier African material associated with habilis/rudolfensis and Dmanisi. And yet Dmanisi has already been widely associated with later African and Asian material assigned to Homo erectus, hence the description of it in various publications as basal Homo erectus.

Put simply, my initial take on these fossils is that they fill an important gap, drawing connections between two somewhat exceptional specimens (KNM ER-1470 and Dmanisi 2600) and a broader evolutionary picture of change in early Homo.

Bernard Wood, in his Nature commentary on the article, makes the argument that these fossils continue to push the range of variation in early Homo too far, evidence for taxonimc diversity at this time (he also suggests several easy to do studies that would inform this debate):

Finally, some researchers have suggested(9,10) that evidence from the face and jaws of H. habilis and H. rudolfensis, plus what little fossil evidence we have of these species’ other body regions, stretches the definition of the genus Homo too far.

 

Perhaps these two taxa belonged to a different lineage from that from which H. sapiens arose?

 

My prediction is that by 2064, 100 years after Leakey and colleagues’ description of H. habilis(3), researchers will view our current hypotheses about this phase of human evolution as remarkably simplistic.

This line or argument reminds me of my previous thoughts on the conflation of simplicity with taxonomic linearity in paleoanthropology.

I do not think rapid evolutionary change within a lineage need necessarily be “simple.” We actually have a great model for thinking about this… ourselves.

The last 100,000 years of human evolution involves fairly rapid evolutionary change. This is true for the hard-tissue elements of our anatomy that preserve as fossils, but even more so for our DNA. Yet this rapid evolutionary change was in no ways simple.

It involved a massive and rapid expansion of human populations out of Africa, significant reductions in human adult mortality, a diversification and intensification of human technological production and use AND genetic exchange with at least distinct and extinct human lineages, the Neandertals and Denisovans.

A model of a single lineage of early Homo need not be simple. As a starting point, we know that there are at least two other closely related lineages of hominins walking around Africa at the time in the form of Australopithecus boisei and whatever Australopithecus sediba represents (its own species, some extension of A. africanus, or something else entirely).

Thus, the presence of taxonomic diversity is already one element present to contribute potential evolutionary complexity.

An even bigger factor is simply what is going on with the evolutionary transformation in early Homo.

Between 2.0 and 1.5 million years there is a significant change, even within specimens that consensus assigns to a single taxon (i.e. Homo erectus) in the form of changing proportionality in the post-cranial skeleton, cranial expansion, reduction in post-canine dental size and related changes in the face and cranial base.

One might conceptualize this as a fairly rapid change from something that is ecologically distinct from living humans and apes, whatever the progenitor of Homo is, to something that has all the trappings of a nascent ecological human (technologically-mediated, cooperative, ecological generalist).

It is clear there is an abundance of morphological diversity in the early African fossil record for Homo. The consensus going back more than 30 years is that this must be a reflection of taxonomic diversity. I am not convinced that we are at that point.

It is quite possible that Bernard Wood is correct and we will look back in fifty years and say we had far too simple a perspective on issues of this time. However, it is not entirely clear to me that such a view necessitates the presence of multiple taxa, overlapping in range, morphology and ecology.

There is a lot more that could be said of these new fossils, comparisons with other fossils, and arguments about their evolutionary significance….all of which will hopefully take place in time.

But for now I will pause and commend the whole team responsible for providing us with these great new fossils.

 

Notes

1. Meave G. Leakey, Fred Spoor, M. Christopher Dean, Craig S. Feibel, Susan C. Antón, Christopher Kiarie & Louise N. Leakey. New fossils from Koobi Fora in northern Kenya confirm taxonomic diversity in early Homo. Nature 488, 201–204 (09 August 2012) doi:10.1038/nature11322

Homo Rudolfensis - Finally Shown to Be a Separate Species?

August 9, 2012

from Evoanth Website
 

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 the genus Homo is quite complex since the human lineage must exist somewhere, along with any other branches H. habilis was related to.

This complexity is further compounded by 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 categorized 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 favor 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 is moot, so the fact we’ve found more fossils is not conclusive proof.

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“) these finds are still very important.

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