Artificial Thickening of Bone and the Piltdown Skull
Nature July 9, 1960
 One of the few things about the Piltdown bones which has not been settled is the unexplained thickness of the cranial bones. The maximum thickness of the parietal bones, for example, is 12 mm. While this can occasionally be matched in a contemporary skull, such a thickness is seldom encountered in a normal skull. Severe chronic anæmia has been suggested as a possible explanation. It occurred to me that fraud might be at least as good an explanation. Since the faker (or hoaxer) faked everything he could, why not also the thickness of the skull bones? But how does one cause skull bones to thicken? A hydroxide would seem a likely agent. Some potassium hydroxide being readily available 4-1/2 oz. were dissolved in 36 oz. of tap-water, and in this solution was immersed the right posterior three-fourths of a human parietal bone of an adult male. The bone was a dissecting-room specimen of an individual who died about thirty years ago, and had been degreased in the customary manner with peroxide. It was immersed at 3.50 p.m. on April 15. After remaining undisturbed, for 6 days in this solution, the bone had considerably thickened and become as soft as butter. The bone was gently removed with a ladle at 4.15 p.m. on April 21, and put on a plate. An attempt to wash it under a gentle spray resulted in the removal of innumerable small particles of bone from the inner and outer tables, which rapidly formed a sediment about 3/4 in. thick and a little more than an inch square. The bone was placed in the open air to dry, which it did within 5-6 hr., accompanied by much flaking away of the inner and outer tables. No attempt was made to harden or otherwise treat the bone. The bone is now somewhat less thick than when it was first removed from the solution, but in its dried somewhat delaminated state it is thicker than the untreated bone, at the corresponding margins, by some 2-2.5 mm. Where the untreated portion of the same skull bone is at the margin (which was artificially produced by a blow with a hammer which broke the skull into four pieces), 6.2 mm. in thickness, the treated bone is at the corresponding margin 8.7 mm. in thickness. I am confident that with a little more patience one could do a great deal better than that.
As in the Piltdown bone so, too, in this artificially thickened bone the diploe has undergone most expansion, while the inner and outer tables have remained relatively thin.
It is not suggested here that the hoaxer used potassium hydroxide to thicken the Piltdown skull bones. It is suggested that quite possibly he used a similar means.
The results of this experiment raise the question as to whether the thickness of palæolithic human skull bones may not, at least in part, be due to the action of various substances in the soils in which they have lain.
My thanks are due to the Department of Geology, Princeton University, for supplying me with the potassium hydroxide used in this experiment.
Princeton, New Jersey
The results of the experiment carried out and described by Dr. Ashley Montagu are certainly most interesting; but they cannot be considered as providing a possible explanation of the unusual thickness of the Piltdown cranial bones, for two reasons: (1) Chemical analyses have confirmed that the Piltdown cranial bones are slightly mineralized, for example, they contain 0.1 per cent adsorbed fluorine; indeed the conclusion that they are sub-fossil has recently been confirmed by radiocarbon dating. Those ?? fossil bones which have lost a considerable proportion of their collagen matrix obviously will not be expanded appreciably by any chemical treatmentat least not to an extent anywhere nearly comparable with that occurring in the case of a dissecting ?? specimen with full collagen content. (2) The ?? uniformity and small size of the diploic space in the Piltdown cranial bones are incompatible with any artificial expansion.
In the British Museum collections here there are other crania with walls not only as thick as those of the Piltdown cranium, but also showing the same combination of naturally thickened diploe and extremely thin inner and outer tables. The two most striking examples are the cranium of an Ona Indian from Tierra del Fuego, which has already been figured in comparison with Pitldown2, and a Bronze Age ???/ from Sutton Courtenay in Berkshire (Oxf. E.113.27).
Sub-Department of Anthropology
British Museum (Natural History)
London, S. W. 7
1 Nature, 184, 224 (1959). WHERE IS 1?
2 Bull. Brit. Mus. (Nat. Hist)., Geol., 2, No. 6, 259 (1955).