New Post on Homo naledi From Darrel Falk and Deb Haarsma

Darrel Falk and Deb Haarsma have teamed up on a new post about the peculiar South African hominin, Homo naledi, a find on which I reported a few days back.  Darrel Falk:

This is a wonderful time to be studying human origins. Scholars used to think that there was a slow steady progression of one single species after another becoming more and more human-like through time. That’s not the way it was at all. Although these fossils give no evidence for when H. naledi went extinct, it’s clear it was our contemporary in Africa for at least a little while. There also were at least several other hominin species outside of Africa at that same time. Some members of our species migrated out of Africa to Eurasia about 70,000 years ago, only to find that Homo neanderthalensis and the related, but distinctive Denisovans were already there. At the same time, the primitive diminutive species, H. florisiensis, occupied an island in Indonesia, and H. erectus was in eastern Asia. Meanwhile, back in Africa, we know from genetic evidence that, in addition to H. naledi, another unknown hominin species was present and interbred with our species as recently as 30,000 years ago. So our lineage shared life on this planet with a whole set of other species up until just a few thousand generations ago.

A bit back, I wrote a BioLogos post where I examined the hominin diversity in the early to middle Pleistocene, in which I asked the question How Many Forms Were There?  In that post, I pointed out that our simplistic notions of hominin taxonomy needed to be seriously re-evaluated. Where we once upon a time thought that there was only one species of hominin between 3 and 3.5 million years ago, there may, in fact, have been anywhere from three to five.  It is becoming more likely that this is a pattern that characterizes human evolution, perhaps, all the way up to the ascendancy of modern humans.  If this is so, then Bernard Wood is correct, in that we have many, many more species throughout the range of human evolution than we thought.  This discovery will cause a radical rethink of how we interpret species in the human fossil record.  Witness the rise of systematics.

Two Hominin Species Running Around At 1.9 Mya

Meave Leakey and some colleagues¹ have unearthed and described some new fossil hominins from Koobi Fora that seem to confirm that, yes, there were two very different critters running around 1.8 to 1.9 million years ago on the plains of eastern Africa. From the Turkana Basin Institute:

Found within a radius of just over 10 km from 1470’s location, the three new fossils are dated between 1.78 million and 1.95 million years old. The face KNM-ER 62000, discovered by field crew member Elgite Lokorimudang in 2008, is very similar to that of 1470, showing that the latter is not a single “odd one out” individual. Moreover, the face’s well-preserved upper jaw has almost all of its cheek teeth still in place, which for the first time makes it possible to infer the type of lower jaw that would have fitted 1470. A particularly good match can be found in the other two new fossils, the lower jaw KNM-ER 60000, found by Cyprian Nyete in 2009, and part of another lower jaw, KNM-ER 62003, found by Robert Moru in 2007. KNM-ER 60000 stands out as the most complete lower jaw of an early member of the genus Homo yet discovered.

The skull being referenced (heavily throughout the press release) is that of KNM-ER 1470, discovered by Richard Leakey in 1972 and dated to 1.9 million years ago. 1470 has a very flat face and is large, so much so that when it was discovered and compared to the Homo habilis material that Richard's dad, Louis Leakey and Napier and Tobias were pulling out of the ground, it was felt that it represented a new species, Homo rudolfensis.

For a short run-down on the material from this time period, go to my BioLogos post, The Human Fossil Record, Part 7: The Rise of Early Homo.

Anyhow, these new fossils add a new level of what Bernard Wood² calls “complexity.” For quite some time, 1470 existed in its own little world, with no fossil remains being similar to it in size or in shape. Questions began to rise about the veracity of its reconstruction and its provenance. These new fossils fit 1470 to a “T” and it now seems clear the 1470 does, in fact, represent a different form than that represented by skulls like ER 1813, which is small and gracile and gives support to the idea that there were two competing species of hominin on the landscape even before Homo erectus/ergaster arrived on the scene some two hundred thousand years later. Below, on the top is KNM-ER1813 and below it is KNM-ER 1470















As you can see, there is considerable difference in overall size and robusticity between the two and when the new material is compared to the mandible KNM-ER 1802, which is similar to 1813, there is a considerable mismatch. What remains to be seen is where Homo ergaster came from.

¹Leakey, M. G., Spoor, F., Dean, M. C., et al. (2012). New fossils from Koobi Fora in northern Kenya confirm taxonomic diversity in early Homo. [10.1038/nature11322]. Nature, 488(7410), 201-204.
http://www.nature.com/nature/journal/v488/n7410/abs/nature11322.html#supplementary-information

²Wood, B. (2012). Palaeoanthropology: Facing up to complexity. Nature, 488(7410), 162-163.
http://dx.doi.org/10.1038/488162a

Au. sediba Now Considered Possible Ancestor to Homo

New research is suggesting that the overall anatomy of Australopithecus sediba makes it the best candidate for being ancestral to Homo.  The article in Science Daily is quite long and delves into the specific traits that Lee Berger suggests are thought to evolving in the direction of Homo.  They write:

Lee Berger, the project leader from the University of the Witwatersrand in Johannesburg, South Africa, explains what these new findings mean for modern humans. "The many advanced features found in the brain and body, along with the earlier date, make it possibly the best candidate ancestor for our genus -- the genus Homo -- more so than previous discoveries, such as Homo habilis"
The age of the Au. sediba fossils has been constrained to about 1.977 million years, which predates the earliest appearances of Homo-specific traits in the fossil record. Until now, fossils dated to 1.90 million years ago -- and mostly attributed to Homo habilis and Homo rudolfensis -- have been considered ancestral to Homo erectus, the earliest undisputed human ancestor. But, the older age of these Au. sediba fossils raises the possibility of a separate, older lineage from which Homo erectus may have evolved.

This position seemed odd to me at first because there is already evidence of “early Homo” dating back to 2.3 million years ago. Then it occurred to me that this article makes a tacit assumption that is not stated: Homo habilis and Homo rudolfensis are not really Homo, but are Australopithecus. This is an argument that has been made by Alan Walker and Bernard Wood who suggest that, despite the size differential between H. rudolfensis and the late australopithecines, they are more similar than different.This levels the playing field and then Au. sediba simply becomes the branch of Australopithecus from which Homo sprung.

Taxonomy is a black art and we run the risk of tying too much significance to our taxonomic designations.  If we argue that Au. sediba gave rise to H. ergaster, despite the fact that there are already two species of Homo running around, it conjures up ideas of convergent evolution where an earlier australopithecine gave rise to Homo habilis and Au. sediba gave rise to Homo ergaster.  If, however we demote earliest Homo down to australopithecine status, the difficulties vanish “like the snows of yesteryear” as Isaac Asimov would say.  Look for this to be challenged as well.