Robin McKie has a feature article about the Piltdown hoax in the Observer today, that makes good reading for those who may not know the history of this case: "Piltdown Man: British archaeology's greatest hoax".
The man [Dawson] had more form than Professor Moriarty. There would be no need to look any further, were it not for some nagging doubts – including one of Chris Stringer's. It's the cricket bat that gets him. "It was huge but apparently everyone missed it until the end of the dig. Until then everything had been carefully engineered: the skull fragments and artefacts, all made to look alike. And then the cricket bat turns up. It is bizarre and only makes sense if you conclude someone wanted to alert the authorities that fraud was going on, but did not want to do so publicly, perhaps to avoid bringing disgrace to the museum. So they planted something so ridiculous that everyone would surely realise it was a fake, a laugh. Unfortunately, everyone took it seriously."
The Natural History Museum will start some new analyses hoping to match the chemical signatures in the bones to a box of dyes and chemicals later found in the possessions of Martin Hinton, an NHM scientist often suspected to have been involved in the hoax. Maybe they'll uncover other facts pertinent to the case.
One of the interesting things I've noticed over the past decade is that Piltdown is passing into obscurity. I find it so fascinating, because Piltdown was the most celebrated "fossil" purported to prove that Neandertals had nothing to do with human ancestry. When it was found, Piltdown was argued to be Pliocene in age! Its very humanlike braincase from much earlier than the Neandertals made it seem that there were different types of humans coexisting throughout our evolution. Piltdown was not the first such specimen -- the Galley Hill skeleton had been found in 1888, some more fragmentary pieces even earlier. Over time, still more specimens were argued to represent a similar pattern -- very modern-looking skulls at very early dates. Anthropologists of the 1910's made a claim that we've often heard expressed as a "revolutionary" idea: human evolution was a bush, not a ladder, and Neandertals belonged to an extinct twig.
We now appreciate that these "early" specimens simply weren't real evidence about the early evolution of modern humans. In the first half of the 20th century, no direct dating of specimens was possible. Site excavations often did not uncover slumping layers or intrusive burials of later skeletons into earlier archaeological horizons. Piltdown was the only outright hoax, but there were many errors of archaeological judgment that pointed in the same direction.
That story obviously changed greatly over the years. The hoax was exposed in 1953, but its shadow would be much longer. In 1954, Henri Vallois presented the "Praesapiens theory", a set of ideas that had been coalescing in the writings of several continental anthropologists for a dozen years [1]. Vallois combined two ideas: Neandertals were too specialized to be ancestors to Aurignacian and later peoples, and these more "modern" forms did have antecedents much earlier in the fossil record of Europe. By that time, not only Piltdown but a long list of other supposed "Praesapiens" specimens had been debunked. Vallois admitted that only two were left: the Fontechevade remains and the Swanscombe skull. But after more than fifty years of commitment to a non-Neandertal human ancestor in Europe, these last scraps were enough for many anthropologists to keep the idea alive.
It is fascinating to see how Vallois dealt with Piltdown in his account of the discredited Praesapiens specimens:
The arguments that have risen round the Piltdown remains are too recent and too close to the feelings for there to be any reason to dwell on this very celebrated find. The researches initiated by Weiner, Oakley & Le Gros Clark have, it seems definitively, shown the lack of age of the human remains and their fraudulent introduction into the site, at the same time as they established, and still more categorically, that the mandible belonged to an ape. No good grounds would exist for returning to these facts if they had not been utilized by some anthropologists as an argument against the existence of Praesapiens. Now if, at the time of its discovery, the so-called Eoanthropus had been considered as a precocious representative of modern man, it would have been quickly rejected from the phylum of the latter by the reason of the aberrant features of its mandible. Almost all the genealogical trees placed it on a side branch without descendants. Well before the sensational disclosures referred to [citing papers debunking the hoax], the idea of Praesapiens had not for a long time relied on Piltdown man, whose exclusion from human fossils properly so called does not thus affect the essentials of the problem.
I guess that's what they call "leading with your jaw." Vallois included a figure that illustrates the phylogenetic schemes of many previous scholars with respect to Piltdown's position:
Figure 4 from Vallois 1954. The original caption reads as follows: "Schematic representation of the genealogical trees of Homo sapiens and Homo neanderthalensis according to different authors: I Pilgrim (1915), II Elliot Smith (1924), III Keith (1927), IV Osborn (1927), V Hooton (1946), VI Kälin (1952). Sap = Homo sapiens, N = Homo neanderthalensis, P = Piltdown, S = Swanscombe, F = Fontéchevade. The broken line indicates the lower limit of the Pleistocene."
By claiming that all these phylogenies placed Piltdown as an extinct side-branch, Vallois was deflecting the issue. It is conventional to depict a fossil on its own branch, for one can never ascertain certainly that a specimen has descendants. In these days before cladograms (which necessarily would give a specimen its own branch), authors used branch length as an indicator not only of closeness of relationship but also of their confidence in the assertion. At any rate, Vallois chose these to illustrate every possible position -- Piltdown as basal to humans together with Neandertals, Piltdown as modern human ancestor, Piltdown within the variation of humans, closer to some living races than others (as in Hooton's diagram). Vallois is correct that many anthropologists never accepted Piltdown as a modern human antecedent -- of course, many of those never believed that Piltdown was anything other than a scientific mistake. It is entirely understandable that the Praesapiens proponents wanted to bury Piltdown as quickly as possible. Piltdown did not, as Vallois wrote, affect the essentials of the problem. But the hoax worked precisely because so many anthropologists believed that a non-Neandertal human ancestor should exist.
The idea of an African origin for modern humans bears a resemblance to the Praesapiens idea, and does share some of its intellectual history. Louis Leakey explicitly hypothesized an African Praesapiens form, and argued that the Kanam jaw and Kanjera fossil hominins represented it. But the later development of the Out of Africa model drew from another deep tradition that interpreted evolutionary transitions as a series of radiations from an evolutionary center. That's another story, one that begins from a very different legacy than the Piltdown idea.