CHAPTER XXI 



THE EVOLUTION AND SIGNIFICANCE OF THE CERE- 

 BRAL CORTEX 



AT the conclusion of our analysis of the structure and func- 

 tions of the nervous system it will be of interest to review very 

 briefly a few topics of a more general sort related to our theme, 

 with special reference to the significance of the cerebral cortex 

 in the general scheme of human evolution and culture. 



For the purpose of our analysis animal activities may be 

 classified under three heads (see p. 31): (1) Innate functions of 

 invariable or stereotyped character developed through natural 

 selection or other biological processes, whose mechanism is hered- 

 itary and common (with small differences only) to all members of 

 a race or species, typified by reflex action and purely instinctive 

 action; (2) variable and modifiable functions, whose pattern is 

 determined by individual experience through which the innate 

 action system is more or less permanently altered, intelligent 

 acts and the reasoning process representing the highest forms of 

 this type, though the lower members of this series are not neces- 

 sarily consciously performed; (3) acquired automatisms, or 

 individually acquired actions which have become so thoroughly 

 habitual as to be performed quite as mechanically as the heredi- 

 tary reflexes. Intelligently acquired actions which have finally 

 come to be automatically and even unconsciously performed are 

 sometimes designated "lapsed intelligence," but such lapsed 

 intelligence must be a purely individual acquisition. There 

 is no evidence that automatisms of this sort can be transmitted in 

 heredity, and, therefore, they can play no part directly in the 

 evolution of instincts, as some have taught. 



The first and second of the types of action above distinguished 

 appear to be common to all organisms, though their relative im- 

 portance varies enormously from species to species. The first 

 type includes the reflexes and all of the pure instinct-actions, 



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