same species. Therefore, we cannot pinpoint any cellular and chemical differ- 

 ences between large and small brains that would indicate a basis for different 

 behavior. Are there differences in behavior and in achievement between indi- 

 viduals with big brains and individuals with small brains? Evidence for such 

 differences does not seem to exist. 



We must confess our ignorance of the functional meaning and value 

 of different sized brains in modern human individuals. 



If we are ignorant of these essential facts about varying brain size in 

 modern man, our ignorance in relation to the interpretation of fossil man 

 is even more abysmal. It is so for 2 main reasons: first, we can never know 

 what the palaeoneurohistology of any early hominid was. (Only the now 

 classical and curious case of the Ganovce endocast from Czechoslovakia 

 may be cited in parenthesis: it was once seriously claimed of this specimen 

 that it was a true fossil brain and not an endocast, and that impressions of 

 the nerve cells could still be detected. Happily, the most recent account 

 of the specimen treats it as an ordinary endocast— Vlcek 1969.) Any state- 

 ments we may make about the course of the probable changes in neural 

 make-up from, say, A. africanus to H. habilis, or from H. habilis to H. erec- 

 tus, would be purely by analogy and deduction. Such statements could 

 never eliminate an element of conjecture and even speculation. 



The second difficulty is that, with endocasts, we are dealing not with 

 a replica of the brain but with an impression of the interior of the brain- 

 case. Therefore, the external form and size of the cast reflects the sum total 

 not only of all the neural and glial factors listed above but also of a further 

 set of variables, namely: (a) the thickness and volume of the pachymeninx 

 or dura mater; (b) the thickness and volume of the leptomeninges, the 

 arachnoid and pia mater, as well as of the subarachnoid space; (c) the vol- 

 ume of the cerebrospinal fluid; (d) the total bulk, thickness, and ramifica- 

 tions of the cerebral and cerebellar arteries meandering over the surface 

 of the brain; (e) the caliber of the cranial venous sinuses, and the size of 

 the cerebral veins and lateral lacunae of the superior sagittal sinus; and (f) 

 the thickness of the cranial nerves, at least that part of them from their 

 attachment to the brainstem to their disappearance into various foramina 

 and bony canals. 



This gives us another 6 variables to add to the previous 7. Thus, when 

 studying endocasts, we are further removed from the detailed organization 

 of the brain. And, a fortiori, we are still further removed from understand- 

 ing the structural basis of behavioral differences and behavioral evolution. 



105 ^ 



