Countering Creationism, Pt. II; “Zinj”

15 05 2007

There are some fossils that, despite the best efforts of scientists, seem to defy descriptive boundaries. The Cambrian terror Anomalocaris, with it’s serrated camera-shutter mouth, has had its seemingly odd assemblage of body parts confused for a fair number of other marine invetebrates throughout its infuriating history. As Stephen J. Gould notes in his famous work Wonderful Life;

Now who ever dreamed about a connection between the rear end of a shrimp, the feeding appendage of Sidneyia, a squashed sea cucumber, and a jellyfish with a hole in the center? Of course, no one did. The amalgamation of these four objects into Anomalocaris came as an entirely unanticipated shock.

Anomalocaris was a vexing beast, to be sure, and although many other fossils don’t have the distinction of once belonging to several different phyla, there are those that have gone through so many name changes and reassignments that it is difficult to keep track of what exactly they should be called. Such is the case with “Zinj“, or the Hominid Formally Known as Zinjanthopus boisei. Paul Humber, loathe to let evolutionary scientists off the hook, asserts the follow in his long list of problems with evolution;

Reason #17: Nutcracker Man (Zinjanthropus boisei), found by Louis Leakey in 1959, was once used to promote the so-called missing-link concept; however, even evolutionists now admit that this extinct creature should not be viewed as ancestral to man.

Humber immediately puts himself on thin ice with this rather weak criticism; I’ve already admitted in thie very essay how sometimes scientists can be greatly mistaken, only to later correct past misconceptions. The difference between Anomalocaris being some variety of arthropod and being a jellyfish is far greater than “Zinj” being moved from being ancestral to man to being part of another evolutionary offshoot. But can Humber be trusted with the details of his assertions? As we discovered yesterday in my post about the much-maligned Hesperopithecus (or “Nebraska Man”), Humber omitted a vast amount of critical information about the fossil and its perceived importance, and it appears that he has once again failed to the the requisite research into just what happened to the “Nutcracker Man.”

On July 17, 1959, Mary Leakey uncovered the first known remains of a new fossil hominid in Olduvai Gorge, Tanzania. Her son, Richard Leakey, describes the discovery of the fossil that was to become known as “Zinj” in his book The Origin of Humankind (1994) as follows;

After almost three decades of searching the sediments of Olduvai Gorge, [Mary] was rewarded with the sight of millstone molars, like those of the robust australopithecene species in South Africa. The Olduvai individual was, however, even more robust than its South African cousin. Louis Leakey, who, with Mary, had taken part in the long search, named it Zinjanthropus boisei: the generic name means “East Africa man” and boisei referred to Charles Boise, who supported my father and mother in their work at Olduvai Gorge and elsewhere. In the first application of modern geological dating to anthropology, Zinj, as the individual became known, was determined to have lived 1.75 million years ago. Zinj’s name was eventually changed to Australopithecus boiseri, on the assumption that it was an East African version, or geographical variant, of Australopithecus robustus.

Perhaps for the sake of brevity, Richard leaves out the fact that Lous was ill at camp when Mary discovered the fossil, but he was excited enough about the find to dub the new specimen Titanohomo mirabilis (more affectionately known among the Leakys as “Dear Boy”). In September of that same year, however, the “Dear Boy” had undergone a name change. Rather than being introduced as Titanohomo mirabilis, his name was changed to Zinjanthropus boisei, placed within the Family Australopithecinae. Louis’ views about the fossils relationship to extant humans, however, did not escape criticism. While Louis believed that Zinj was perhaps a direct human ancestor based upon morphology and tools found at the site, others suggested that Zinj truly belonged to the genus Paranthropus (where it now resides), but this view did not appeal to Louis as it would put the “Dear Boy” out of the running to have a direct role in human evolution.

Yet, as was suggested by Richard’s excerpt above, the fossil has been shifted between taxonomic groups more than once. In the beautifully illustrated (but apparently now outdated) book From Lucy to Language (1996) by Donald Johanson and Blake Edgar, the authors consider Zinj to be a seperate robust species within the genus Australopithecus (boisei remained the species name). Regarding the taxonomic situation of Zinj at the time the book was written, the authors relate the following;

Louis Leakey’s suggestion that Zinj was a distinctive sort of early human ancestor is now universally accepted, even though the genus name, Zinjanthropus, has been dropped in favor of Australopithecus. Detailed examination of other finds, especially from Koobi Fora, substantiate the unique facial skeleton of A. boisei. In a notable study of comparative and functional anatomy, The Australopithecene Face, Yoel Rak defined a host of morphological features found in the face that make boisei a unique species. The palate is strongly retracted; the zygomatic (cheek) bones have migrated forward, extending into a visor-like support for the masseter muscles; and the supraorbital tori slope away from the midline, giving the face a “sad” expression.

[For the sake of completeness, Zinj is also listed in the genus Australopithecus in the NOVA companion book Ancestors: In Search of Human Origins by Donald & Lenora Johanson and Blake Edgar (1994)]

And so it became apparent that while Zinj was a hominid of related ancestry to the line that would give rise to extant humans; he was not a direct ancestor as originally surmised. Ironically enough, however (and as noted before), Zinj now resides not in the genus Australopithecus but Paranthropus, the very one proposed by some of Leakey’s critics when the fossils were first brought to light. Ian Tattersall and Jeffery Schwartz, in their 2000 book Extinct Humans, describe the seeming confusion this way;

Although Louis dubbed the new hominid Zinjanthropus boisei in his 1959 announcment in Nature, “Zinj” (catalouged as OH 5 to denote its status as the fifth hominid specimen from Olduvai) would remain its nickname. Because the tendency at the time was to follow Ernst Mayr in reducing the number of hominid genera, many paleoanthropologists thought that naming Zinjanthropus was too much, although it would do as a species of Paranthropus. But by the time that Phillip Tobiar, Dart’s successor at Wits and a collaborator of the Leakeys, published the descriptive volume on Zinj in 1967, the taxonomic tide had turned completely toward Mayr’s opinion that the morphological differences among all australopiths were relevant only at the level of species. So Paranthropus robustus became Australopithecus robustus, and thus Zinj became Australopithecus boisei. Subsequently the tide turned again, and nowadays not only are Australopothecus and Paranthropus up and running as distinct genera, but there are questions emerging about whether the species placed within each genus are particularly closely related to each other and even whether, collectively, australopiths constitute an evolutionary group.

Indeed, it seemed that the desire to lump specimens together and find THE lineage that led to humans superceded the apparent differences in the fossils, and the human “fossil trail” (to borrow from the title of another excellent Tattersall book on human evolution) seems to be more convoluted than originally thought. Shortly after the passage cited above, Tattersall and Schwartz note that the move away from “wastebasket” genera was a big step for paleoanthropology;

Eventually, Richard Leakey and colleague’s discovery in the 1980s of a skull somewhat similar to, but not exactly alike, the robust and hyper-robust australopiths would lead to the revival of the species aethiopicus. At some point the dam would have to break. For, how much longer could paleoanthroplogists follow Mayr’s dictum of unilinear human evolution and keep putting skulls and jaws into the same wastebasket of a species before someone was bound to say, “Hey, these don’t look like the same thing”? And fortunately, thanks to the work of Richard Leakey and his collaborators, the specimens that continued to be discovered kept adding to the improbability that Mayr had been correct about hominids. To the contrary, it seemed, the human fossil record-at least the older and less threatening part of it-was a record of diversity. The question was, and continues to be, how one goes about sorting it out.

It seems clear from Paul Humber’s assertion involving Zinj that he wished to sow doubt among those unfamiliar with paleoanthropology (or the science as a process in general); how can these scientists claim to know so much if they keep moving things around? If I were Paul I would be careful about telling people to hold grudges because of academic mistakes; he misconstrued the story of Hesperopithecus as discussed yesterday, as well as getting Zinj’s current taxonomic status (and actual discoverer, Mary Leakey) wrong.

Some of you may even be wondering why I spent so much time on such a weak argument; why would I head out to the library, return with an armful of books, and spend two hours reading and typing away to combat such a simple assertion? The answer would be that I am no expert in human evolution and I honestly wanted to know the answer (as well as finding such paleontological tales to be interesting). Even beyond my personal interest, I want to be able to present the truth (inasmuch as I am qualified to do so) to you, the reader. It’s easy to make a blind assertion without backing it up, wishing to win an argument rather than to increase knowledge, but (at least in this case) I prefer doing things the hard way. In essence, the changing status of Zinj does not pull the rug out from under evolutionary theory or debase the notion that humans evolved from primate ancestors; the status of Zinj as a direct human ancestor seemed awfully tenuous to begin with, and just as with “Nebraska Man” wa found out to be a peccary though study and accumulation of data, new evidence allows scientists to further refine Zinj’s place in evolutionary history (though at the moment there’s still plenty of debate). Indeed, I fully expect that Zinj’s taxonomic affinities may change again in the future, but this does not somehow disprove evolution or our relationship with other primates; if Paul Humber had done more than parrot standard creationist dogma he would have recognized this and perhaps would have been able to construct a more substantial argument. Science does not live or die by the hypotheses of Louis Leakey, Henry Fairfield Osborn, Charles Darwin, or any other scientist you care to name; it is a process of coming to understand nature that always has the hope of correcting itself and accounting for past errors, and such vital flexibility is inherently lacking in creationist dogma.


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2 responses

18 05 2007
Laelaps

[…] May 18th 2007, 9:41 pm Filed under: Behavior, Evolution, Books In preparation for my posts about Zinj and Hesperopithecus, I took out nearly every book the New Brunswick Public Library had on […]

25 07 2011
Quentin Berlinger

I have been absent for a while, but now I remember why I used to love this web site. Thanks, I’ll try and check back more frequently. How frequently you update your web site?

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