Friday, April 13, 2012

Fossils, not cookies, or, what I've been thinking about lately...

Oreopithecus bamboli.

Yeah, no. I'm not writing about creme-filled cookies here. Instead, I'm talking fossils.

Here lately, I've been all about fossils, because I'm writing a book about physical (or biological) anthropology and archaeology, and fossils are a big part of physical anthropology. It's all fascinating. It's also very difficult to write about, especially when you're writing for beginning, who more than likely don't have a great grounding in science and might not have much of a grasp on anything having to do with human evolution, who might even have religious or philosophical issues with any kind of evolutionary theory, much less the idea that modern humans evolved through a series of forms before we got to who we are today.

As an example, there is Oreopithecus bamboli. O. bamboli is a Miocene ape, fossils of which have been found in Tuscany and Sardinia in Italy. This species lived 7 to 9 million years ago and has been touted as evidence that bipedalism didn't just evolve in hominids (that was David Pilbeam, or Harvard University).

In the 1950s, Johannes Hurzeler found fossils representing this species and proposed, based on indications that it could walk upright, that it was a human ancestor. His conclusion was widely criticized, with some other researchers saying that any resemblance to hominids was strictly coincidental, a case of convergent evolution. Others didn't even see a resemblance to any creature on the line to humans.

Case closed, right?

Well, this is paleontology, the study of fossils and closely related to paleoanthropology, the study of the human fossil record, so, no. Paleontologists and paleoanthropologists argue about most things related to their field most of the time, or so it seems.

In the 1990s, Meike Kohler and Salvador Moya-Sola, both from the Miquel Crusafont Catalan Institute of Paleontology in Spain, took it upon themselves to reanalyze the Oreopithecus collection in a Swiss museum. After their research, the two concluded, as had most before them, that the fossils represent an ape and is not on the line that led to modern humans. But they also said that the spine and lower body show a resemblance to the australopithecines and to modern humans, and that its hands were capable of a precision grip.

One exception to the general conclusion that Oreopithecus' lower anatomy is hominid-like is that its big toe diverges 90 degrees from its other toes. Then again, several of the proposed earliest ancestors to humans also have divergent big toes. Just something else to speculate about and argue about; how close does a hominid foot have to resemble a modern human foot for that hominid to have walked bipedally enough like a human being to be considered to be a relative of modern humans, directly or indicrectly?

Kohler's and Moya-Sola's explanation for Oreopithecus' traits, which were characterized as intermediate between apes and australopithecines, was that the specimens they looked at had lived on a swampy island, were threatened by no predators, and thus could spend a lot of time on the ground, which led to its development of the ability to walk for short distances on two feet.

Again, others have said they do not see the hominid-like traits Kohler and Moya-Sola reported, and one researcher, Randall Susman, from Stony Brook University in New York, pointed out that these fossils are difficult to evaluate in any case, because they are poorly preserved.

Which leaves us where? Writing in The Last Human (Yale University Press, 2007), Esteban Sarmiento, a research associate at the American Museum of Natural History, said that "Oreopitheucs suggests that features, such as the shape of the pelvis, lower back length, a knee joint with a carrying angle, a skull with a downward directed opening for the spinal cord, and non-interlocking canines, all of which have been used to classify fossils as hominids, are probably shared by the common human-African-ape ancestor, and do not distinguish a human lineage exclusive of African apes."

And this is why it is so difficult to write about human evolution. All we are left with is bones, some of them very old, very poorly preserved, and very difficult to evaluate accurately. Not only that, but most of the time there is no complete skeleton of an individual, and sometimes not even complete bones. We can't see what these fossils species looked like dressed in their skin, and we can't see how they behaved. This makes figuring out who evolved into whom a guessing game.

A game of educated guesses, to be sure, but a guessing game nonetheless.

Which, I hasten to add, does not mean that evolution did not happen. It simply means that the story of how that evolution proceeded is very hard to discern and that paleoanthropologists and biological anthropologists will be putting together the clues for a long time to come.

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Some of the information about Oreopithecus bamboli in this post comes from online reports appearing in Science News and Smithsonian Magazine.

3 comments:

LadyLazarus said...

This is so interesting. The history of human origins gets more and more diverse every year.....

littlemissattitude said...

Isn't it, though. I've been fascinated with the whole subject since I was just a child. The book I'm writing, which I mentioned in this post is meant to be a serious guide for students starting out in physical anthropology and archaeology. It will be published, one way or another. But, I really feel sometimes like I'm indulging myself by writing it, because it is just so much fun, and so interesting, to work on.

The thing that really amazes me is how much more we know now, and how much more evidence we have now about human origins compared to when I started reading about the subject, years ago. There are at least twice the number of known species than there were then, in the 1960s.

By the way, thanks for stopping by to read and comment.

Est Ban said...

Most of what we know of our evolution comes from studying those living animals that are most closely related to us. Fossils tell us how diverse our lineage and those of our relatives was in the past.de2