DEVELOPMENT OF BEHAVIOR 325 



adaptive one. Hence the series goes no farther (since the cause for 

 reaction ceases at once), and these organisms are not killed at all by the 

 injurious condition. They are thus selected, as compared with those 

 reacting in the usual way, and their method of reacting, being congenital, 

 is inherited by posterity. In the course of time all the remaining indi- 

 viduals of this group will respond at once, like those of the previous 

 group, by the reaction 7. 



Thus individual selection and natural selection necessarily work to 

 the same result. One selects from among the different acts of the same 

 individual, the other from among those of different individuals. The thing 

 selected is the same in each case, — namely, the adaptive reaction. 



If there exist at the same time the power of individual modification 

 and the variations on which natural selection acts, then under uniform 

 conditions the latter will be more effective, since it results in immediate 

 response by the adaptive reaction, while the former requires that every 

 new individual should go through the trial series, with its attendant 

 dangers of destruction. If the conditions are very severe, in time only 

 the individuals which have inherited the immediate adaptive response 

 will survive. Thus, through the action of natural selection these or- 

 ganisms will have an inborn tendency to react directly in an adaptive 

 way, whereas in previous generations most of the individuals of the race 

 acted in this manner only as a result of individual modification through 

 experience. 



Furthermore, it may be pointed out that in the course of time an 

 organism which had adopted some special type of behavior, as burrow- 

 ing, would become quite unadapted to other behavior, as running along 

 the bottom or swimming through the water. It develops structures, 

 under the influence of its adaptive behavior, that make it difficult or 

 perhaps impossible for the organism to react in any other way than by 

 burrowing. After a time, then, it will lose all tendency to react in other 

 ways, because it cannot react in other ways, owing to the structural 

 changes it has undergone. In most cases the specialization will not go 

 so far as this, and the organism will retain the power of attempting other 

 methods of reaction; that is, of performing other movements. But 

 these movements will be ineffectual, because the structures of the or- 

 ganism are not adapted to their performance. They will therefore 

 not relieve the organism from stimuli ; hence they will be quickly 

 exchanged for the movements which are effective. Thereafter the or- 

 ganism will always react by these movements on which its structure is 

 based. If these first few ineffectual movements are not observed, it 

 will appear that the organism has been rigidly limited from the beginning 

 to this one type of behavior. Apparently there exist few if any organisms 



