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, 
