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SCIENCE PROGRESS 



that is, combined the massive ramus of the one with the large 

 teeth and simian mandibular symphysis of the other? The 

 genealogy of the four species concerned would then be as 

 shown in fig. 4. This second hypothesis obviates the neces- 

 sity of assuming a reversed evolution in the case of the 

 Heidelberg jaw, and the low forehead of the Neandertalers 

 may be once more explained as degeneracy, it being assumed 

 that " X," like Eoanthropus and sapiens, had a high forehead. 

 But the theory encounters formidable difficulties. It is clear, 



H. sapiens. 



H.neandertalensis. 



H.heidelbergensis. 



Eoanthropus. 



Fig. 3. 



for instance, that if it be true, the narrower ascending ramus and 

 the deeper sigmoid notch were acquired independently by 

 Eoanthropus and sapiens — that is, that these similarities are no 

 sign of kinship, but are due to parallelism in development. In 

 this connection it is interesting to notice that if the outline of the 

 jaw of a European be superimposed upon that of heidelbergensis, 

 the chin region of the European's jaw projects beyond the front 

 of the ancient jaw, just as that of Eoanthropus projects in Fig. 2, 

 only rather less so. Since, however, modern jaws have a chin 

 prominence, which Eoanthropus certainly had not, the front 

 curve of the jaw passes backwards again as it passes upwards, 



