ADAPTATION IN NATURE 353 



places and modified its flow It moulds its banks and bottom, 



forming here a bar, there an island, here a bay, there a point of iand, 

 but still flowing on, though its course, its speed, its depth, the character 

 of the substances which its carries in suspension or in solution, all are 

 altered, built up by its own past activity." According to this view, 

 structure is simply the resultant of the interaction of function and en- 

 vironment or of functional activity. Though perhaps a little extrerr.i 

 for most of us, this view is, we believe, essentially correct. We an- 

 prone to overemphasize structure in our discussions of adaptation 

 and evolution and to lay too little stress upon the energy side ot 

 development. Certainly no structure is ever formed without proto- 

 plasmic activity of a very definite sort, and in this sense adaptations 

 are to be thought of as the results of functioning. Why, then, do we 

 claim to be astonished at the effective way in which certain organs 

 accomplish their functions, when functioning has taught them their 

 task? 



TWO CATEGORIES OF ADAPTATIONS 



There are, according to E. G. Conklin, two categories of adapta- 

 tions: (a) racial or inherited adaptations, and (b) individual, acquired, 

 or contingent adaptations. All of the direct molding effects of environ- 

 ment or of developmental functioning, together with adaptative rela- 

 tions resulting from habitat selection or from learning and experience, 

 may well be classed as individual, acquired, or contingent adaptations. 

 As such they do not offer any particular problem to the evolutionist, 

 for they concern themselves with individuals, not with races. The 

 adaptive condition is simply made over afresh in each generation, and 

 the only thing that seems to extend beyond the immediate individual 

 or generation is a general plasticity or responsiveness of the specific 

 protoplasm which enables it to adjust itself to special life conditions. 

 There is nothing mysterious or baffling about this situation, for it in- 

 volves merely a repetition of certain appropriate responses by each 

 individual. It is a problem of individual development, not of racial 

 development or evolution. 



Inherited Adaptations. — There is, however, a large category of 

 adaptations which appear in the organism as though in anticipation 

 of the role they are to play some time in the future and not in response 

 to any present need. In this category are the eyes, the lungs, the vocal 

 organs, the taste buds, and many other organs of the human fetus. 



