Comparing Apes With Fossils

Forgive the awkward title. There are a wide variety of misunderstandings about how paleoanthropologists practice their science. While I am reluctant to continue flogging dead stinky horses, a good example of a common misconception occurred over at UD. You may remember this post of Orac’s lamenting the embrace of ID by David Cook, MD. Mr. Cook has also made some comments concerning paleoanthropology that I would like to discuss, as they display some common, and widespread, misunderstandings of paleoanthropology. I was going to pass over Mr. Cook’s comments in silence, but since I have encountered similar comments in a wide variety of places I finally decided to write something and address them.

In a follow up comment at UD Mr. Cook comments:

The recent front-page story on the ancient skull discovered in Kenya, and your editorial of March 24 about it, are perfect examples of the tautological reasoning which cripples real advances in the study of the origins of life. There is nothing about that skull itself, taken without preconceived assumptions, to suggest that it is an ancestor of modern humans.
Here is how it goes; an anthropologist discovers an old skull or skeleton. Since he knows that humans descended from earlier primates, he immediately interprets the old bones as probable ancestors of humans. He then announces that he has discovered more evidence that humans descended from primates.

A little later in the same comment he says:

What was actually discovered in Kenya was a very old primate skull. Period. Everything after that is inference. To me it looked like a gorilla, or other great ape. How many great ape skulls have been left lying around Africa over the years?

Leaving aside the fact that Mr. Cook failed to support the latter contention with any kind of evidence, the implication is that paleoanthropologists are incapable of telling the difference between apes and humans. Or perhaps, that they don’t consider primate anatomy when discussing fossil finds. How accurate is this characterization of paleoanthropology? In a previous post I compared the anatomy of Chimps, gorillas, orangutans and Australopithecus afarensis and I don’t propose to go into details concerning the differences between apes, humans and hominin fossils. What I would like to look at is the use of comparative material.
Let’s start with Pierolapithecus catalaunicus. P. catalaunicus is an ape dating to approximately 13 million years ago. It is an important fossil because it is close to the last common ancestor of great apes and humans. When Moya-Sola et al announced the find, however, they did not just make a series of assertions and then claim that P. catalaunicus was close to the last common ancestor of the great apes and humans. They compared it to a wide variety of extant and extinct apes and cercopithecoids. For example, they compared P. catalaunicus to Dryopithecus, Proconsul, Ouranopithecus, Morotopithecus (among other extinct primates), Hylobates, Ateles, Pongo and Papio (among other extant primates).
When Brunet et al announced the discovery of Sahelanthropus tchadensis they compared it to Pongo, Pan, Gorilla, Samburupithecus, Ouranopithecus the australopithecines (including Paranthropous), Ardipithecus, Homo habilisand Kenyanthropous among others.
When White et al announced the discovery of Australopithecus ramidus (later transfered to the genus Ardipithecus) they compared it to the other australopithecines, Pan, Gorilla, Sivapithecus, Kenyapithecus, Ouranopithecus, Dryopithecus, and Lufengpithecus among others.
When Asfaw et al announced the discovery of Australopithecus garhi they compared it to the other australopithecines, early Homo and Pan
When Senut et al announced the discovery of Orrorin tugenensis they compared it to the other australopithecines, Ardipithecus, Pan, and Gorilla.
The point to take away from all of this is that when paleoanthropologists announce a new species they are expected to compare it to other relevant species, be they extinct or extant. This practice of comparing a new species to other species is also prevalent in paleontology. In fact I seriously doubt a new species could be named without this kind of comparison (in technical jargon it is called a diagnosis). What about other uses of comparative material? How often, outside of naming a new species, do paleoanthropologists compare there fossils to extant species of primates? I will only give a few examples of this in order not to bore you.
Richmond et al compared a 16 million year old ulna to a wide variety of extant and extinct primates.
Senut et al (2004) compared the scapula and clavicle of Nacholapithecus kerioi to 15 extant primates as well as Proconsul heseloni, Ugandapithecus major, and Equatorius
Young used cladistic analysis, principle components analysis and cluster analysis to examine the post cranial anatomy in a wide variety of extant and extinct primates.
One final study. Alemseged et al (of Dikaka fame) examined fragments of the frontal, both temporals, occipital, parietals, and the right maxilla of some previously undescribed fragments from Omo. Part of the examination consisted of comparing the morphology displayed by these fragments to similar bones in Australopithecus aethiopicus, A. boisei , and A. robustus.
The above examples are not exceptions to the rule. I could spend the next week cataloging all the articles that compare primate anatomy with fossil material and still not exhaust the literature. In reality, comparing finds with extant and extinct primates forms one of the central missions of paleoanthropology. Comparative material exists in a wide variety of museums, anthropology departments and medical schools. Over and above that, a large part of the education of a paleoanthropologist consists of learning primate anatomy (both skeletal and soft tissue). In point of fact, any paleoanthropologist who didn’t compare his fossils with other extant and extinct species wouldn’t be taken to seriously.
One final point. I frequently hear people claim that a given hominin fossil “looks like” an ape. This is remarkably vague, although perhaps forgivable if one doesn’t know that much about skeletal anatomy. Given the abundance of comparative material, however, this is something that can be looked at metrically (by taking measurements on relevant variables and performing various statistical analyses) and non-metrically (via the analyses of specific morphological characters). Consequently, when you here some one asserting that a fossil “looks like” and ape with out further specification you can assume that they are either being deliberately evasive or they do not know what they are talking about (or both).
Literature Cited (in order of appearance)
Moya-Sola et al (2004) Pierolapithecus catalaunicus, a New Middle Miocene Great Ape from Spain. Science 306:1339-1344
Brunet et al (2002) A New Hominid from the Upper Miocene of Chad, Central Africa. Nature 418:145-151
White et al (1994) Australopithecus ramidus, a New Species of Early Hominid from Aramis, Ethiopia. Nature 371:306-312
Asfaw et al (1999) Australopithecus garhi: A New Species of Early Hominid from Ethiopia. Science 284:629-635
Senut et al (2001) First hominid from the Miocene (Lukeino Formation, Kenya). Earth and Planetary Sciences 332:137-144
Richmond et al, 1998 First Hominoid from the Miocene of Ethiopia and the Evolution of the Catarrhine Elbow, Vol 105:257-277
Senut et al (2004) Preliminary Analysis of Nacholapithecus Scapula and Clavicle from Nachola, Kenya. Primates 45:97-104
Young (2003) A Reassessment of Living Hominoid Postcranial Variability: Implications for Ape Evolution. Journal of Human Evolution 45:441-464
Alemseged et al (2002) Hominid Cranium From Omo: Description and Taxonomy of Omo-323-1976-896. American Journal Of Physical Anthropology 117:103-112