Mailbag: Bromage's KNM-ER 1470 reconstruction, systematic position of Homo habilis

5 minute read

(this letter refers to my 2007 comments on Tim Bromage’s KNM-ER 1470 reconstruction)

Dear Professor Hawks,
You may dispute Dr Bromage's work on skull 1470 which effectively relegates "rudolfensis" to the Australopithecine genus rather than as some intermediate type approaching Homo erectus - and I tend to lend more credence to a computer simulation than a medieval water displacement method - but it doesn't really change anything. It is still a lone specimen and the 700cc cranial vault volume is at the upper range for some gorillas, certainly macrocephaliac ones.
You might also want to look at a paper in Nature by Fred Spoor entitled "Implications of new early Homo fossils from Ileret, east of Lake Turkana, Kenya"...
http://www.nature.com/nature/journal/v448/n7154/full/nature05986.html
.... which I think we can safely say confirms that habilis too was a species within Australopithecus genus which in turn is not actually a direct ancestor of modern humans according the the findings of an Israeli team that discovered gorilla-like mandibles in A afarensis remains:
http://www.pnas.org/content/104/16/6568.full And the finds of Dmanisi suggest a pygmy-like sub-race of Homo erectus which still appear very human-like in this reconstruction by National Geographic of the skulls found in a cave in Georgia. http://ngm.nationalgeographic.com/ngm/0504/feature2/multimedia.html Anyway, this is just my humble opinion, although I am fairly certian that any direct lineage from ape ancestors to modern man has effectively collapsed as far as the fossil record is concerned.

Thank you for your comments. Taking your last point first, you seem to imply that Homo habilis (and Australopithecus) are apes, and Homo erectus is a human, and there is no “direct lineage” in between. If you find this idea persuasive, I think you should give some more study to the morphology of Australopithecus.

With respect to Bromage’s reconstruction, I hope you don’t misunderstand my point about water displacement (which you call a “medieval” method). Using a ruler is a medieval method of measuring distance. If the ruler tells me that my foot is a foot long, and the computer tells me it’s only 8 inches, I’m going to be very skeptical about the “simulation” on the computer. Likewise for a computer reconstruction that apparently removes a third of the volume of a well-preserved endocast.

In any event, Bromage and colleagues (2008, J. Clin Ped Dent) published a revised estimate of 700 ml. I think this is also an underestimate considering Holloway’s methods, but it is very far from the claim of 526 ml that had appeared in 2007.

It is a mainstream position within paleoanthropology to place H. habilis (or H. rudolfensis) into Australopithecus (for example, see articles by Bernard Wood and Mark Collard, or Milford Wolpoff’s Paleoanthropology text). The reason for this placement is usually the small body size and relatively large teeth of H. habilis compared to H. erectus, which may indicate an australopithecine-like niche.

Modern humans have extensive variation in brain size, as do other primates. A single specimen with a brain size of 750 ml within a population that averaged around 500 would not be very unusual. So I agree with you that the size of the brain of KNM-ER 1470 by itself cannot determine the position of H. habilis.

But KNM-ER 1470 is far from alone, and the median size of other specimens (OH 7, OH 24, OH 13, OH 16, KNM-ER 1813) is around 600 ml. That is an increase of at least 30 percent on average compared to A. afarensis, A. robustus or A. boisei. Your point is correct that large male gorilla crania may be over 750 ml. Gorillas are three times the body mass of H. habilis, and in any event do not average 600 ml.

A number of other specimens are less complete or equivocal (they could be H. erectus), including KNM-ER 1805, KNM-ER 1590, and KNM-ER 3732. But their brain sizes do not change the mean; including them in H. habilis (or H. rudolfensis) would not reduce the difference of that species from Australopithecus.

The Dmanisi hominids are certainly interesting. My inclination is to see H. erectus as a polytypic species that varies substantially in body size, just as recent humans do. In that context, a stature of 160 cm is normal, while a shorter stature of 140 cm is small-bodied but not more than many recent hunter-gatherers. The brain size of the Dmanisi hominids is very close to those reported for H. habilis, without considering any correction for body size.

(The writer replied:)

A 6 foot tall hominin appears in the fossil record from about 1.9 MYA distinctly different from other specimens: Its brain size is at the lower end of modern human range, its humerus-femur index is 0.7 as with modern humans, its semi-circular canal is not suitable for the kind of balance needed for arboreal life, its shoulders do not indicate it can brachiate, it is an obligate biped whose wrists show it could not knucle-walk. It is human in every sense - maybe not a homo sapiens, but certainly another type of human.

That was certainly my opinion up to around 2002; I wrote a 2000 article that argued that the large-bodied Homo represented a really new kind of hominid. These days I’m not so sure. The Nariokotome skeleton is relatively late, and the only evidence for large body size at 1.9 million years is the KNM-ER 3228 innominate bone, which we would now interpret as a broad pelvis, but (in light of the Gona pelvis) possibly not a very tall stature.

I am skeptical about skull 1470 in general because, like most fossils, it was found in fragments and had to pieced together - it may also have been deformed by natural processes. Unless you can find more specimens like it, I really don't see how you can justify creating a separate taxon for it, and the same goes for the Gawis skull. Regards

Good to be skeptical, but remember that 1470 is not alone. Bernard Wood’s 1991 Koobi Fora monograph is worth reading through; he did a good job with these issues. Not all agree (I don’t with all parts) but it’s the essential starting point.