HUMAN EVOLUTION 



we cannot tell as much from the surface of the endocranial cast 

 as from the brain itself. The exact details of the fissures can- 

 not be predicted from the endocranial cast alone. Fortunately, 

 we can tell a little about the general degree and pattern of 

 fissuration and the relative size of the various lobes. As the 

 brain is an exceedingly important part of man, it is a happy 

 circumstance for human paleontology that the general features 

 of its surface anatomy may be reconstructed from fossil evidence. 



We may illustrate this general line of argument by consider- 

 ing the brain of Proconsul, which is known from a partial endo- 

 cranial cast. In the simplicity and arrangement of the cortical 

 fissures, Proconsul resembles the Old World monkeys rather than 

 the pongids or hominids. Also the petrous bone (which houses 

 the inner ear) of Proconsul has a large subarcuate fossa. This 

 fossa, or depression, found in monkeys generally but not in the 

 great apes or hominids, holds the floccular lobe of the cere- 

 bellum. The available evidence suggests the brain of this early 

 Miocene ape was primitive and monkey-like compared to the 

 brain of the living apes, of Australopithecus, and of the later 

 hominids (Le Gros Clark and Leakey, 1951). Not enough of 

 the skull of Proconsul is preserved to make a good estimate of 

 its cranial capacity— a rough estimate based on the published 

 drawings would be of the order of 175 to 225 cc. 



The brain of the australopithecines reaches a volume of from 

 450 to 550 cc. This is within the range of brain size in the 

 living great apes, but you must remember that the australopithe- 

 cines were relatively small hominids, with a body weight for 

 adults as low as 70 to 90 pounds, so that relative brain mass 

 would be larger in the near-men than in a living gorilla. Several 

 available endocranial casts indicate that the surface features of 

 the cerebrum in Australopithecus is of hominid, and not pongid, 

 design (Schepers, 1946). In Pithecanthropus, hominids of about 

 the same body size as modern man, the endocranial volume 

 overlaps the lower normal size limit in Homo, with a mean of 

 860 cc. for the Javanese, and of 1075 cc. for the Chinese, speci- 

 mens. And as might be expected from the archaeological record 

 of their behavior, the brains of Pithecanthropus show the be- 

 ginnings of the expansion of the temporal and parietal lobes 

 characteristic of modern man. 



Recent studies on functional localization in the somatic sen- 



89 



