Origin of Different Kinds of Adaptations 375 



Individual Adjustments as Adaptations 



As pointed out in the first chapter, there is a group of adap- 

 tations, obviously including several quite different kinds of 

 phenomena, that can at least be conveniently brought to- 

 gether under the general rubric of individual adjustments or 

 regulations. A few examples of these will serve to show in 

 what sense they may be looked upon as adaptations, and how 

 they may be regarded from the evolutionary point of view. 



Color Changes as Individual Adaptations 



The change in color of certain fish in response to the color 

 of the background, the change in color of some chrysalides 

 also in response to their surroundings, appears to be of some 

 use to the animals in protecting them from their enemies. 

 The change in color from green to brown and from brown 

 back to green in several lizards and in some tree frogs is 

 popularly supposed to be in response to the color of the sur- 

 roundings, but a more searching examination has shown that, 

 in some cases at least, the response has nothing to do with 

 the color of the background. 



In the first cases mentioned above, in which the response 

 appears to be of some advantage to the animal, the question 

 may be asked, how have such responses arisen ? The selec- 

 tion theory assumes that those animals that responded at 

 first to a slight degree in a favorable direction have escaped, 

 and this process being repeated, the power to change has been 

 gradually built up. The mutation theory will also account 

 for the result by assuming the response to have appeared 

 as a new quality, but it has been preserved, not because it 

 has been of vital importance to its possessor, but simply 

 because the species possessing it has been able to survive, 

 perhaps in some cases even more easily, although this is not 

 essential. Even if the change were of no direct benefit, 



