in the morphological evolution of the Hominidae. The rate, continuity, 

 and duration of change in brain size seem on present evidence to exceed 

 even those processes of dental and gnathic reduction that are such remark- 

 able features of hominid evolution. The trend toward increased brain size is 

 the most continuous, lone-lastine, and marked hallmark of hominization. 



Usually, when such a trend is detected in a fossil sequence, it is ac- 

 cepted that the feature in question has survival value. It is accepted that so 

 sustained a line of development results from the operation of natural selec- 

 tion and that the feature in question is being positively selected. We may 

 be inclined to say, therefore, that larger brain size must have conferred an 

 undoubted advantage and that, down through the ages, larger-brained 

 variants must have enjoyed greater opportunities for survival than smaller- 

 brained ones. 



What kind of advantages could a larger brain have conferred? We 

 must assume that the larger brain incorporated more numerous and more 

 intricately structured neural complexes, which permitted more complex 

 functional patterns to be developed, which in turn endowed the organism 

 with behavioral nuances and propensities, which equipped it better for 

 survival to child-bearing age and reproduction. So, if we speak of the selec- 

 tive advantages of a bigger brain, we should add, "and all that went with it." 

 For this is simply tantamount to saying that the selective advantage of the 

 bigger brain resided in the nature of the behavioral patterns that the bigger 

 brain made possible. The brain was not selected for its bigger size as such; 

 the behavior patterns were selected— and it is just a convenient shorthand 

 to say that bigger brains had survival value and were favored by natural 

 selection. We can make such statements, even though we do not yet know 

 all the intricate maze of systems that intervene between both ends of the 

 chain, that is, gross brain size and behavior patterns. But we must never lose 

 sight of the shorthand in which we are talking. 



The chain of interrelations of parameters may be represented thus: 



Increase in brain size 



J[ 

 Increase in complexity of internal organization 



jr 



Changing functional patterns 



jr 



Changing patterns of behavior 



US l< 



