of fissuration." I was aware, too, of the considerable subjective element 

 that has often entered into such studies, especially when applied to inter- 

 racial comparisons; of the fact that it is most difficult, and for some characters 

 virtually impossible, to express such observations in precise metrical form; 

 and of the comment by the distinguished neuroanatomist, Dr. Gerhardt 

 von Bonin, after a lifetime of studies on brains and endocasts: "It should 

 at last be admitted that most of what has been said and written on the 

 sulci of the brain as they have been seen on endocasts is worth very little" 

 (von Bonin 1963, p. 50), a view that is shared by not a few of those mentioned 

 above. These are among the reasons why I have chosen to confine this study 

 to brain size and endocranial capacity. 



It started, as I have said, as a single lecture and, as such, possesses a 

 single unifying theme. Briefly stated, it is this: nothing is more striking and 

 more sustained in the whole of human evolution than the twofold trend 

 towards increase in brain size on the one hand, and, on the other, towards 

 cultural activities, cultural mastery, and, indeed, utter dependence on cul- 

 ture for survival. These two sets of changes are indissolubly linked. The chain 

 between them may be set forth simply as follows: increase in brain 

 size ?± gain in intricacy of neuronal organization ^± rise in complexity of 

 nervous function ^± ever more diversified and complicated behavior re- 

 sponses ?± progressively amplified and enhanced cultural manifestations. 



This essay explores the first and last steps of this causal chain— the 

 steps that are directly manifest in the fossil record. It pleads that these two 

 items are valid fields of study, each in its own right, irrespective of the 

 tangled skein that may connect them. With Stephan (1969), this essay accepts 

 that "The functional capacity of a system depends upon its size and structural 

 differentiation" (italics mine); that, in addition, "The two variables of struc- 

 ture—size and differentiation— in general do not vary independently," but 

 that ". . . the differentiation can vary in many ways (e.g. in construction, 

 arrangements and connection of the cells, units, layers, etc.), whereas for 

 variations in size there are only two possibilities: enlargement or reduction" 

 (Stephan 1969, p. 34). This work fully recognizes the importance of the 

 intervening areas of knowledge. In fact, it very gingerly peers into the murky 

 fastnesses of the fossil neuron, the glia-neuron ratio and relationship, the 

 feedback chains, and other components of the middle links that will one 

 day establish the logic and the causality uniting the termini. Into this 

 no-man's land, at present, only the intrepid few are venturing. It is in these 



