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September 26, 2002

Pitt professor skeptical about recent "oldest human" discovery

A recent discovery of possible human ancestor fossils announced this summer in the scientific journal Nature has been hailed by some scientists as being among the most important anthropological discoveries in the last 100 years, both for the believed age of the fossils and for the location of the find.

But Pitt anthropology professor Jeffrey Schwartz is skeptical of the claims.

A skull, jawbone and teeth thought to be 6 million-7 million years old — predating all other known human ancestor fossils, or hominids, by as much as 3 million years — were discovered in Chad in central Africa, and not in the East African Rift Valley, long considered the birthplace of humanity.

Schwartz acknowledges that the discovery represents "something different. It doesn't look like anything I know," he says. "It might be a new species. Whether it's a hominid is another question. But you can't tell much from the pictures without examining the fossils themselves"; the discoverers of the Chad fossils have permitted only limited access to certain other scientists.

Anthropologists don't agree about what makes a true hominid, the anthropological group that includes humans and their fossil relatives, Schwartz says. "Most think enamel on teeth and bi-pedalism, that is, walking on two legs and therefore having the hole at the base of the skull centrally located through which the spinal cord passes" are the most important criteria.

Schwartz maintains that studying biological factors contributing to the origin and subsequent diversification of species as well as human skeletal analysis need to be part of the mix.

"Anthropologists usually classify specimens by site," that is, where they were found, Schwartz says. "You can't limit yourself to that, because biological comparisons go across sites. So I'm interested in comparing things in ways that haven't been done before. When people say, 'I'm going to go study this particular group; I'm going to study Homo erectus, or Neanderthals,' I question first, Why is it a group? And then you start in a different place."

In the case of the Chad findings, researchers say the fossil skull shows an ape-like brain casement, with a short face and teeth that resemble those of a human. The skull fragment is different enough from existing fossils, the discoverers claim, that it has been assigned a new genus and a new species, Sahelanthropus tchadensis.

Chad officials have nicknamed the specimen "Toumai," a name meaning "hope of life" in a local language.

"People who are naming new genera and species plan the release of these findings with great hoopla," Schwartz says. "The findings enter into the media and textbooks, but nobody knows for sure what the hell they are."

As a physical anthropologist whose specialty is systematics and taxonomy (the science, principles and process of classifying organisms), Schwartz says most scientists who study finds of this kind study only human evolution. "When people study human fossils, they tend to study size and shape: it's big, it's round, it's flat, it's whatever.

"That's why you can call Neanderthals a variant of us, because there are some humans with bigger skulls and some with flatter skulls. But the same thing applies to sheep; you're not going to expand the realm of human fossils to include sheep — or, I would say, even chimps!" which are considered by most scientists to be humans' closest living relative.

Schwartz says humans and chimps share obvious similarities, but the same is true of other animals. "[We] also share some with a crocodile. We have five digits, like a reptile. That's why there's a hierarchy to the uniqueness or commonality that must be considered."

Schwartz proposed a radical theory in the early 1980s that in fact the orangutan and not the chimpanzee was the closest relative to humans. While examining molecular as well as fossil data, he found a handful of features humans have in common with African chimps, but more than two dozen shared features with orangutans, the shaggy, red-haired apes typically found in the jungles of Sumatra and Borneo.

He noticed particularly that orangutans and humans, to the exclusion of chimpanzees and gorillas, developed a unique anatomical feature of the palate, which also is found in fossil hominids. In addition, humans and orangutans have low cusp molars with thick enamel, a trait not shared by African apes.

"The point is that mammals will vary in similar ways: There will by smaller ones and rounder ones," Schwartz says. "Clearly, the closer related to each other, the more similar will be the ways in which individuals in different species vary. But because they vary in similar ways, that doesn't mean that they meld as a species, it just means they vary in similar ways."

As an example, Schwartz says, comparing two different skulls for "variables" misses the point. "You really don't mean variable, you mean how different they are. There's a need to sort out the significance of the differences and similarity. I've come from studying other animals, and what you see is a strong diversity everywhere. So, when it comes to human evolution, I say, what's this uni-lineal stuff?"

And anthropology as a science and especially anthropology textbooks are filled with wrongheaded comparisons, Schwartz maintains, which led him and a colleague to pursue a grand-scale task: compiling the first compendium of the human fossil record.

"I've been frustrated teaching because I haven't been able to give my students neutral interpretations," Schwartz says. "Students needed a source, and so did I, frankly. All presentations in anthropology texts are done comparatively, and usually human evolution is compared with the chimp. We need to be able to look at a hierarchy of evolutionary significance among differences."

So almost 10 years ago, Schwartz and his colleague Ian Tattersall, curator of anthropology at the American Museum of Natural History in New York, embarked on compiling the complete "Human Fossil Record," a three-volume set with descriptions, photographic images, diagrams and drawings.

Volumes 1 and 2 have been published and volume 3 is due to publisher John Wiley and Sons early next year.

"The way in which fossils are generally described is in comparison with something else: It's bigger than this, it's smaller than that, it's flatter than this, it's rounder than that. So you never know what the fossil is, you only know that it doesn't look like these other things," says Schwartz.

He set up a protocol to ensure the descriptions are written in the same fashion from specimen to specimen, so that each is being described using the same criteria.

"We wanted students to have a resource that they can use for thinking on their own, instead of merely taking findings as data. So, really, people who don't subscribe to our methodology necessarily can still use it. I hope it will stand as a resource to be used in the spirit of which we conceived it, a learning tool. And I'm glad we did it, because I think it will never be duplicated."

Schwartz says he and Tattersall have tried to examine the Chad fossils, which he says belong in volume 3 of the fossil record. But they have been stymied by the discoverers. Unlike in most scientific disciplines, anthropologists sometimes publish findings without making their evidence public for all to study, he says.

"[The discovers of Toumai] want us to embrace everything they say about it, but they won't let us examine it. These findings are important, but in terms of being presented scientifically, I think they're violating the rules."

The rules of the International Code of Zoological Nomenclature state that publication of new a genus or species requires openness, Schwartz says.

"But people are not following those rules and there isn't a court, if you will, governing this. In molecular studies, you can't even publish [without allowing the public to view your findings]. The same should be true for fossils, especially human fossils."

Schwartz chocks up the scientists' attitudes in part to big egos.

"You discover one hominid tooth and your life changes. You get money, you get glory, you get in the textbooks, you might even get paranoid. But if they want it to be part of the conversation, they have to let other people see it."

–Peter Hart

Filed under: Feature,Volume 35 Issue 3

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