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This idealization was perhaps to be expected, because according to modern evolutionary theory Sinanthropus (or Homo erectus) is supposed to be the immediate ancestor of Homo sapiens. But Boule (1937), considering reports coming from Choukoutien, said: “To this fantastic hypothesis, that the owners of the monkey-like skulls were the authors of the large-scale industry, I take the liberty of preferring an opinion more in conformity with the conclusions from my studies, which is that the hunter was a real man and that the cut stones, etc., were his handiwork” (Fix 1984, pp. 130 –131).

Why did Boule say the skull of Sinanthropus was monkeylike? There are several reasons. One, of course, is the large brow ridges. When the skull of Sinanthropus is seen from directly above, the ridges stick out like handlebars on a bicycle (Figure 9.1, p. 556). Another apelike feature is the “postorbital constriction,” or narrowing of the skull in back of the eye sockets. Humans do not have this. Place your fingers at the corners of your eyes and then run them back to your temples, just above the ear. You will notice that the surface is flat. But in Sinanthropus, immediately in back of the eyes, there is a very pronounced indentation on either side ( Figure 9.1). Another apelike feature is the general shape of the skull when seen from behind. The skull of Sinanthropus is somewhat narrower at the top than at the bottom ( Figure 9.1). In contrast, human skulls are normally wider at the top than at the bottom (Boule and Vallois 1957, p. 135). Also, as previously noted, the walls of the Sinanthropus skull are twice as thick as those of the average human skull.

Figure 9.1. The first Sinanthropus skull, discovered in 1929 at Choukoutien, viewed from above (Jia 1975, p. 17) and from the rear ( Boule1937, p. 7). Like the apes, Sinanthropus has enormous brow ridges and a pronounced postorbital constriction (top). Also, the Sinanthropus skull, seen from the rear (bottom), is narrower at the top than at the bottom, another apelike feature.

The capacity of the Sinanthropus cranium is said to average around 1000 cubic centimeters, more than the anthropoid ape average of 600 cubic centimeters but less than the human average of about 1400 cubic centimeters. There have been suggestions that Black and Weidenreich reconstructed shattered Sinanthropus skulls in such a way as to increase their cranial capacity above the range for apes. Concerning the initial skull recovered in1929, Bowden, after careful study of Black’s three reports and accompanying photographs, noted that the bottom edge of the reconstructed skull pictured in the last report was lower than the bottom edge shown in the first photograph, taken shortly after the skull was excavated. Bowden believed this discrepancy could be accounted for if one assumed the lower part of the skull had been carelessly cropped out of the original photograph. More likely, according to Bowden (1977, p. 118), was the possibility that the “reconstruction of the base of the skull was carried out in such a way that it was made deeper” thus yielding a larger and less apelike volume.

Boule pointed out that there was strong sexual dimorphism in Sinan thropus. That is to say, there was great variation between the size of males and females, much more than in human beings. This is an apelike feature, which is reflected in the Sinanthropus jaws found at Choukoutien (Figure 9.2). Weidenreich noticed the dimorphism when studying reconstructed jaws of a male, female, and child, which showed unusual variation in size. Boule stated: “The total result was so polymorphous that Weidenreich wondered whether it was really a single species, or at least a single race. It is a fact, however, that this polymorphism is a simian characteristic in singular contrast to the slight sexual dimorphism in human jaws” (Boule and Vallois 1957, p. 138). Another apelike feature of the Sinanthropus jaw is that it has several openings for the dental nerve that reaches out to the skin of the chin, while the human jaw has only one (Keith 1931, pp. 262