238 LIGHT AND THE BEHAVIOR OF ORGANISMS 



are adaptive, but if they are confined in a glass jar with a 

 bunch of seaweeds at one end and an intense light at the 

 other they collect at the illuminated side and remain there 

 and die, whereas if they had become negative they would 

 have been saved by the shelter of the seaweeds. But could 

 they, even from a rational point of view, be expected to 

 react otherwise under conditions which neither they nor 

 their ancestors have experienced? 



If the positive reaction which guides a moth into a candle 

 is a non-adaptive reaction, then the positive reaction which 

 guides the wolf searching for food into a baited pitfall must 

 also be considered non-adaptive. But what would happen 

 to the wolf if he did not react positively to food; does not 

 the trapper expect him to get into the pitfall ? Is not the 

 flight of the moth into the flame, after all, precisely what 

 one would expect if its reactions to light in general are 

 adaptive? 



Even in case of positive reactions of animals which live 

 in darkness, as e.g. the caterpillar of the willow borer and 

 the mud-inhabiting crustacean Cuma rathkii, referred to by 

 Loeb (1906, p. 159), or the cave-dwelling fishes mentioned 

 by Eigenmann (1899), it is probable that the reactions were 

 inherited from ancestors in which they were adaptive. 

 Reactions to light which are non-adaptive, except under 

 artificial conditions, are certainly rare. And whatever the 

 fundamental cause may be, it is evident that organisms in 

 general in their natural habitats tend to aggregate in regions 

 which have conditions adapted to the needs of their life 

 processes. We shall have occasion to emphasize this in 

 the following paragraphs. These conditions may differ for 

 different species and different individuals and for the same 

 individual from t'me to time. 



Of course the fact that reactions are adaptive does not 

 explain their origin. Natural selection may tell us why 

 organisms are as they are. It shows why adaptive charac- 

 teristics continue to exist while the non-adaptive ones do 

 not, but it does not tell us how they originated or why they 



