Evolution Basics: From Primate to Human, Part 3
Note: This series of posts is intended as a basic introduction to the science of evolution for non-specialists. You can see the introduction to this series here. In this post we discuss the change in scientific consensus in the mid twentieth century to the view that the Australopithecines were hominins – and the revelation that Piltdown Man was a fraud.
Australopithecines – the long road to acceptance
In the last post in this series, we discussed the seminal discovery of Australopithecine fossils by Raymond Dart and the cool reception they received by the scientific establishment of the time. In the 1920s, the epicenter of science was England, and the English had their “missing link” bridging humans and apes – the fraudulent Piltdown Man, with its then-expected ape-like body and a human-like brain. This erroneous “brain first, body second” view of human evolution meant that the true hominin fossils then known (Dart’s Australopithecus and Dubois’ Pithecanthropus (Homo) erectus) were “backwards”, with human-like bodies matched to inappropriately small brains. As we have seen, Dubois’ finds were widely thought to be chance assemblages of human skeletal remains with an ape skull; similarly, Dart’s interpretation was criticized based on his specimen being a juvenile. Without an adult form to examine, it was surmised that he had merely discovered a species closely related to modern apes.
Dart did gain some allies, however – and two in particular would assist him in slowly turning the tide of scientific opinion to his interpretation of the australopithecines as true hominins. The first was Robert Broom, a somewhat eccentric paleontologist and Fellow of the Royal Society who would work with additional australopithecine fossil discoveries in the 1930s. One such find was an exceptional fossil skull Broom would describe as Plesianthropus transvaalensis, a species distinct from Dart’s Australopithecus africanus. From its scientific name the fossil would soon acquire the moniker “Mrs. Ples”, an affectionate nickname that has stuck despite its later reclassification as an adult Australopithecus africanus rather than a separate australopithecine species. A few years later, however, Broom would discover a genuinely new hominin fossil – a species of stocky, muscular australopithecine he would name Australopithecus robustus (a species closely related to the australopithecines that was later renamed Paranthropus robustus). These additional finds greatly bolstered Dart’s position, since they too had the “body first” characteristics in contrast to Piltdown Man.
Dart’s second ally came in the person of Wilfrid Le Gros Clark, also a Fellow of the Royal Society, and well-respected by the scientific establishment. In 1947 Clark would write an influential paper on the australopithecines, chastise the establishment for passing judgment on them without examining them for themselves as he had done (as only a polite, yet scathing Englishman of the time could), and exonerate Dart and Broom in the process:
On the basis of the evidence presented by the first announcement of the discoveries of the Australopithecine fossils, there seemed at first sight to be several possible interpretations. The Australopithecinae might be nothing more than extinct varieties of ape closely akin to the chimpanzee and gorilla, but with certain modifications which in some minor respects show a spurious resemblance to the Hominidae. Secondly, they might have no special relationship to the gorilla and chimpanzee, but, nevertheless, represent a collateral group of anthropoid apes showing certain human characters developed as the result of a parallel evolution but not necessarily indicative of any real affinity with the Hominidae. Lastly, the Australopithecinae could be regarded as extinct hominoids which, while still at (or, at least, close to) the simian level in their cerebral development, were early representatives of the human branch of evolution and thus quite distinct from the Pongidae. This last interpretation has for a number of years been reiterated by Dart and Broom. On the other hand, other anatomists and paleontologists (particularly those who have not had the advantage of examining the original fossil material) have, either by direct statement or by implication, favoured one of the first two interpretations. As the result of his personal studies, the present writer has come to the firm conclusions (1) that the Australopithecinae have no special relationship to the recent anthropoid apes except so far as they are large hominoids of comparable size, and (2) that the human resemblances in the skull, dentition and limb bones are so numerous, detailed and intimate as virtually to preclude the introduction of the idea of ‘parallel evolution’ in order to explain them. In other words, there must be a real zoological relationship between the Australopithecinae and the Hominidae.
And so, the establishment came to see what is in hindsight obvious: the australopithecines were not merely the close relatives of modern apes, nor even such relatives that happened to acquire human-like characteristics through (rampant) convergent evolution. Rather, they were what Dart and Broom had maintained all along: extinct forms that were our close relatives – more closely related to us than to any living ape.
With the weight and stature of Le Gros Clark behind them, the evidence that Dart and Broom had painstakingly accumulated over decades finally gained scientific acceptance. Indeed, the weight of the evidence from the australopithecines – and Dubois’ earlier correct interpretation of Pithecanthropus (Homo) erectus now was seen for what it was: that the form of human body had evolved first, followed by an expansion in brain size. With this picture now in sharp focus, Piltdown stuck out like a sore thumb – and its days as an icon of human evolution were numbered.
The end for Piltdown would be swift in coming, and Le Gros Clark would be one of the key figures in unmasking Piltdown for what it was. Already in the late 1940s a new dating test using fluorine had shown Piltdown’s skull to be of modern, not ancient age. Further analysis would reveal the extent of the deception – the skull of a modern human, the jaw of an orangutan, the teeth of a chimpanzee filed down, all stained with chemicals to look ancient. In the early 1950s the unraveled hoax would hit the popular press – a mystery solved, except for the identity of the forger. Though many individuals have been discussed as suspects in the following decades, the weight of evidence favors the original “discoverer” of Piltdown Man – Charles Dawson – who was the sole “discoverer” of the second Piltdown find, and, as it has been shown, forged many other lesser-known “discoveries” in hopes of fame and scientific standing. If he indeed was the forger, Piltdown was his crowning accomplishment, but he would take his secrets to an early grave in 1916 – without his desired knighthood or an appointment to the Royal Society. Regardless of who was responsible, Piltdown would cast a long shadow over the work of honest scientists such as Dubois and Dart – frustrating their attempts to advance what was a much more accurate view of human origins.
Lessons from Piltdown
Though Dubois and Dart faced an uphill battle, they did have a notable advantage: the nature of scientific advancement. As we noted right at the beginning of this series, evolution is a scientific theory – and as such, Dubois and Dart, with their genuine discoveries, needed only wait for additional work to move hominin paleontology onto a more solid scientific footing and provide a context for evaluating their efforts. The price they paid was not for being correct, but rather for being first, for which – even apart from fraud – there is often a price to pay in science. Piltdown would only prolong the problem, but in science, eventually the truth will out – for only the truth, or something close to it, is useful for making new, accurate predictions.
In the next post in this series, we’ll summarize the current state of the evidence as it pertains to hominin evolution, and place the origins of our own species in that context.
For further reading
- Le Gros Clark, W.E. (1947). Observations on the anatomy of the fossil Australopithecinae. Journal of Anatomy 81; 300-333.
- Brain, C.K. (2003). Raymond Dart and our African origins. In A Century of Nature: Twenty-One Discoveries that Changed Science and the World. (Garwin, L. and Tim Lincoln, T., eds). University of Chicago Press.
- Fossil Hominids, Human Evolution: Thomas Huxley & Eugene Dubois.
- James Kidder: The Human Fossil Record.