Table 10: Sexual dimorphism of hominoid cranial capacity 



(adult female mean expressed as a percentage of adult male mean) 



We may summarize the latest 

 data available for sexual dimor- 

 phism of cranial capacity in the apes 

 as follows: 



Siamang 97.6 



Gibbon (H. lar) 97.0 



Chimpanzee 93.1 



Orangutan 86.2 



Gorilla 8^.2 



It is clear that modern hominoids differ appreciably in sexual dimor- 

 phism of cranial capacity. This fact is important, as several students have 

 used combined-sex samples in their studies (for example, Vallois 1954; 

 Dart 1956). Differing degrees of sexual dimorphism might impart vary- 

 ing distribution characteristics to combined-sex samples, even were the 

 represented proportions of the 2 sexes equal. In fact, the sexual com- 

 position of the available combined-sex samples itself varies widely. Thus, 

 the combined-sex sample of orangutan capacities, totaling 402 values, 

 comprises virtually equal numbers of male and female capacities (203 

 males, 199 females). On the other hand, the combined-sex sample for 



% 46 



