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paleoanthropology, genetics and evolution

Photo Credit: A cast of the Piltdown specimen at Maropeng, South Africa. Photo: Anrie, from Wikimedia Commons

Lessons of Piltdown doubters

Darren Naish at Tetrapod Zoology has published a nice post about early doubters of the Piltdown fossils: “Piltdown Man and the Dualist Contention”.

The scientific establishment recognized that the supposed Piltdown hominin fossils were forgeries in the early 1950s. But long before that time, even shortly after the initial description of the fossils, many scientists doubted that the specimens actually could have came from a single individual. The jaw fragment attributed to Piltdown 1 was too much like those of living apes, and the skull fragment too humanlike for them to make much sense as skull and jaw of a single primate.

Maybe the most far-seeing of the critics was Gerrit Smith Miller:

Miller (1915) concluded that the jaw represented a European chimp which he dubbed Pan vetus. The cranium, he thought, should be referred to the genus Homo and the name Eoanthropus, he proposed, should be discarded. Because the jaw and cranium were missing those parts that would ordinarily reveal the way in which they articulated, Miller (1915) noted that “Deliberate malice would hardly have been more successful than the hazards of deposition in so breaking the fossils as to give free scope to individual judgement in fitting the parts together”.

Naish discusses Aleš Hrdlička’s reaction to the fossils. Hrdlička is remembered in American archaeology as one of the greatest skeptical thinkers in the history of science. He adopted the hypothesis that humans had reached the Americas only after glacial times, and famously worked toward debunking several claims of extremely early human skeletons in the United States. Hrdlička published his observations on the original Piltdown specimens in 1922, with several passages that deserve quoting.

Here’s what he had to say about the lack of congruity between the mandible and skull of Piltdown 1:

The first strong impression which the [mandibular] specimen conveys is that of normality, shapeliness and relative gracility of build rather than massiveness. When, after studying the specimen for a good part of two days, the observer took in had the thick Piltdown skull, there was a strong feeling of incongruity and lack of relationship, and this feeling only grew on further study. As a rule there exists a marked correlation between the massivity of the skull--particularly if as in this case the upper facial parts were involved in the same--and the lower jaw. A finely chiselled mandible of medium or sub-medium strength belongs as a rule to a skull that is characterized in the same way, and vice versa. To connect the shapely, wholly normal Piltdown jaw with the gross, heavy Piltdown skull into the same individual, seems very difficult. After prolonged handling of both the jaw and the skull there remained in the writer a strong impression that the two may not belong together, or that if they do the case is totally exceptional.

That passage may seem striking, not because of how right Hrdlička was, but of how wrong he was.

Hrdlička formed the opinion that the jaw fragment was fundamentally different from chimpanzee jaws, and therefore likely a human ancestor. That conclusion may have owed much to the fact that Hrdlička did not compare it to orangutans. At any rate, his conclusion was the opposite of that formed by Gerrit Smith Miller, who believed the jaw must have belonged to a chimpanzee, while the skull was fundamentally human. Hrdlička did not undertake a detailed examination of the skull in his 1922 paper, and seems to have thought it was massive and robust, setting it apart from recent humans.

About the molar labeled as a part of “Piltdown 2”, which Dawson had claimed was found 2 miles from the skull and mandible of Piltdown 1, Hrdlička had this to say:

The additional molar tooth of the Piltdown remains is in every respect so much like the first molar of the Piltdown jaw, that its procedure from the same jaw seems certain, and it would seem probable that the account of its having been discovered at a considerable distance away might be mistaken. The tooth agrees with those of the jaw perfectly not only in dimensions and every morphological character, but also in the degree and kind of wear. A duplication of all this in two distinct individuals would be almost impossible.

Hrdlička may not have intended this to be quite as provocative a claim as it might appear today. At the time that Arthur Smith Woodward revealed the Piltdown 2 discovery in 1917, Charles Dawson (who supposedly discovered the specimens) had been dead for a year. Hrdlička certainly was suggesting carelessness by Dawson, or miscommunication between Dawson and Smith Woodward. After all, Hrdlička had seen many instances of careless specimen collection leading to misunderstandings in the United States. With Dawson dead there was no way of simply asking.

Eleven years later, Smith Woodward replied to Hrdkička’s comment in a short letter to Nature.

Fortunately, among old correspondence, I have just found a postcard of July 30, 1915, written by Mr. Dawson, in which he announces his discovery of this molar tooth "with the new series". I have given the postcard to the Geological Department of the British Museum (Natural History), so that the record may be preserved and made available for reference.

I can’t help but read Hrdlička with the strong sense that if this had been an early human discovery in the United States, his skepticism about the fossil’s reported context would have been more potent. In the U.K., postcards from fossil collectors and the word of prestigious scientists provided all the context anyone could ask.

Many historians of science have discussed the incongruity between the ready acceptance, at least within the English scientific establishment, of the provenience and purported great geological age of the Piltdown material, and the great skepticism–often by the same scientists–of discoveries in Africa.

A number of anthropologists, led by Dart himself along with Phillip Tobias, thought that the Piltdown discovery made for a “perfect storm” of doubt about Australopithecus. By the standards of the 1910s and 1920s, the Piltdown discoveries came with almost impeccable geological context, accompanied as they were with well-known Early Pleistocene mammal bones.

This is a scientific case in which the skeptics were many, even from the start. Hindsight tells us that skepticism was fully justified. One lesson that students should learn about this case is the value of open airing and discussion of skeptical views.

Full body reconstruction of Piltdown
Full body artist's reconstruction of "Sussex Man", by Amédée Forestier in the London Illustrated News, 1912.

The hoax should have been obvious even in 1912, from file marks on the teeth, but these were overlooked. Contemporary skeptics could not openly admit, or did not dare guess, that the bones were the product of a deliberate and malicious forgery.

At the same time, the skeptics showed many of the weaknesses of the science in the early years of the twentieth century. The impressions of skeptical professionals often totally contradicted each other. They could look at the same specimen and have opposite conclusions. Hrdlička and Miller are two great examples of this. They both disbelieved the conclusions drawn by people like Smith Woodward and Arthur Keith. But at the same time, they disagreed almost fundamentally with each other. Their observations were careful, but they lacked a comparative sample. Hrdlička defends his observations by saying that Miller didn’t have the opportunity to inspect the original specimens.

Today, at the beginning of the twenty-first century, some professional anthropologists still deploy that explanation. They say that observations must be taken on original specimens, and scientific descriptions cannot encompass the details visible in originals.

To me, that is the opposite of a scientific perspective. Sure, a poor description may misrepresent an original fossil specimen. Attempts at reconstruction may fail to achieve a true representation of the anatomy.

But we must work toward improving these descriptions. If they cannot be replicated, then they cannot inform our scientific ideas.

It took new technology and the death of a generation of scientists to overturn the place of the Piltdown fossils in human evolution. Getting rare and exceptional evidence wrong caused years of mistaken effort. Paleoanthropologists must grapple with rare, sometimes singular, evidence. Other sciences deal in larger sample sizes, where unusual data points can be ignored as outliers. But in paleoanthropology, “outliers” cannot be ignored.

Yet in a field where many finds are made on land surfaces with no in situ geological context, we must also recognize that some fossils may appear to be outliers because their discoverers have erred in their context. That problem continues, even without deliberate falsehoods like the Piltdown specimen. We must find ways to strengthen context, and be clear about the cases where context is weak.

References

De Groote, I., Flink, L. G., Abbas, R., Bello, S. M., Burgia, L., Buck, L. T., ... & Kruszynski, R. (2016). New genetic and morphological evidence suggests a single hoaxer created ‘Piltdown man’. Royal Society Open Science, 3(8), 160328.

Hrdlička, A. (1922). The Piltdown jaw. American Journal of Physical Anthropology, 5(4), 337-347.

Woodward, A. S. (1933). The Second Piltdown Skull. Nature, 131, 242-242.

Straus, W. L. (1954). The great Piltdown hoax. Science, 119(3087), 265-269.