THE HISTORY OF THE PRIMATES 



erect posture, and it has proceeded more slowly. As the brain case has 

 enlarged, the jaws have decreased in size, with the result that the face 

 has gradually receded to a position tinder the brain case, rather than in 

 front of it as in all other mammals. As already pointed out, the premolar 

 and molar teeth form parallel rows in the apes, while in man, all of the 

 teeth form a gently curved arch (Figure 67). Several differences in the 

 teeth may be mentioned, apart from size. The canines of man are no 

 larger than the adjacent teeth, while those of apes are powerfully devel- 

 oped tusks. The first lower premolar of the apes is modified as a shearing 

 tooth to work against the upper canine, whereas in man the first lower 

 premolar is a typical bicuspid grinding tooth. Also, the surface of the 

 molars of the apes is rather elaborately etched, in contrast to that of man. 

 Finally, man has recently developed the chin, a protuberance on the lower 

 jaw which is unknown in any other mammal. 



Pleistocene deposits in Europe are dated according to the alternating 

 periods of glaciation and warmer times which characterized the Pleisto- 

 cene. There were four major advances of the glaciers separated by three 

 interglacial periods. The fourth postglacial period has now been in prog- 

 ress for something like 25,000 years, and it constitutes the Recent epoch. 

 Dating of the glacial periods is quite uncertain, but we may provisionally 

 accept the following estimates. The first glaciation began about 600,000 

 years ago, and lasted perhaps 75,000 years. The second glaciation began 

 about 500,000 years ago, and lasted about as long as the first. The second 

 interglacial period was much longer, for the third glaciation began only 

 about 250,000 years ago. Its duration was again about the same as the 

 first two. The final glaciation began about 120,000 years ago, and has been 

 receding for about 25,000 years. 



The Heidelberg Jaw. One European fossil appears to be of an age 

 comparable to Pithecanthropus. This is the massive Heidelberg jaw, found 

 in 1907 near Heidelberg, Germany, in a gravel pit which also included 

 bones of known early Pleistocene mammals. It is rather human in general 

 aspect, except that it lacks a chin, and the teeth are quite human, but the 

 entire structure is on a size scale unknown in modern man. It has been 

 described under the name of Homo heidelbergensis. No subsequent finds 

 have yet come to light. 



The Piltdown Fraud. In 1911 and 1912, Charles Dawson, an amateur 

 collector, recovered parts of a skull and lower jaw from a gravel pit near 

 Piltdown, England. The skull was thick but remarkably human, the jaw 

 quite anthropoid, and it soon became the center of controversy. Its pro- 

 ponents regarded it as the earliest known fossil man, claiming that such 

 a combination of human and simian characters was to be expected in the 

 most primitive man. Their opponents considered it to be a spurious asso- 

 ciation of human and ape bones. Stone and bone implements were found 

 in the same deposit, and were claimed (or disclaimed) as evidence of a 

 simple culture. In 1949, a reinvestigation of this fossil was begun at the 

 British Museum, to which Dawson had presented the material. Tests of 

 fluorine content (fluorine accumulates in buried bone) showed that 

 whereas the skull was perhaps 50,000 years old, hardly a relic of the early 



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