per cent. It would appear from these figures that female orang capacities 

 are somewhat more variable than those of males. 



Among gorillas, V for male capacities ranges from 7.41 to 13.30 per 

 cent, the values for 414 pooled males being 10.67 P er cent - Corresponding 

 figures for female gorillas are 7.46 to 10.34 per cent, with a value of 9.91 

 for 254 pooled females. 



In modern man, variability is high, with an estimated V of 12.57 to 

 14.87 per cent for a male sample. 



Hence, in general the cranial capacity tends to be more variable the 

 bigger it is: V for male gorilla, orangutan, and chimpanzee being 10.67, 

 9.19 and 9.76 per cent, respectively. Among females, the same relation- 

 ship holds for gorillas and chimpanzees, with Vs of 9.91 and 8.74, respec- 

 tively; but the female orangs seem to be rather anomalously variable 

 with a V of 10.60. 



On the use of combined-sex samples. Several students have made 

 use of Vallois's (1954) figures: these, it should be stressed, are entirely of 

 combined-sex samples. For such samples, V ranges from 7.71 to 13.06 

 per cent, leaving aside the figures for Homo sapiens. With these com- 

 bined-sex samples, the 3 great apes sort themselves even more clearly: 

 the values of V for mean cranial capacity of gorilla, orangutan, and chim- 

 panzee are 13.06, 10.98, and 9.69 per cent, respectively (Table 9). 



The wide range and high variability of gorilla cranial capacities may 

 reflect, in part at least, a greater degree of sexual dimorphism in gorilla than 

 in other anthropoid apes. 



Sexual dimorphism of hominoid cranial capacities. Different degrees 

 of sexual dimorphism of mean cranial capacity occur among the hominoids. 

 Thus, Oppenheim (1911-1912, p. 138) cites the following figures for the 

 mean capacity of females expressed as a percentage of the mean capacity of 

 males: gibbon 98, chimpanzee 95, orangutan 90, gorilla 85. Zuckerman 

 (1928) gave 91.5 per cent as the corresponding figure for his chimpanzee 

 series. Schultz's (1965) figures are rather similar to those of Oppenheim, 

 except in the orangutan, for which he found a much lower percentage, that 

 is, a much higher degree of sexual dimorphism. His figures are as follows: 

 gibbon 97, chimpanzee 92, gorilla 83, orangutan 81. Table 10, based on the 

 data collated in my earlier tables, gives a tolerably complete list of per- 

 centage ratios of adult female means to adult male means. 



45 S£ 



