12 Evolution and Adaptation 



Figure i A, and at the same time the terminal flap bends over 

 the open mouth of the throat, " stopping the entrance to the 

 flies, which have now nothing more to do here." 



Adjustments of the Individual to Changes in the 

 Environment 



The most familiar cases of adjustments of the individual to 

 the environment are those that we recognize in our own 

 bodies. After violent exercise we breathe more rapidly, and 

 take deeper inspirations. Since during exercise our blood 

 loses more oxygen and takes in more carbon dioxide from the 

 muscles, it is clear that one result of more rapid breathing is 

 to get more oxygen into the blood and more carbon dioxide 

 out of it. The process of sweating, that also follows exercise, 

 may be also looked upon as an adaptive process, since by 

 evaporation the skin is kept cooler, and, in consequence, the 

 blood, which at this time flows in larger quantities to the skin, 

 is cooled also. 



More permanent adaptive changes than these also take 

 place as the result of prolonged use of certain parts. If the 

 muscles work against powerful resistance, they become larger 

 after several days or weeks, and are capable of doing more 

 work than at first. Conversely, when any group of muscles is 

 not used, it becomes smaller than the normal and capable of do- 

 ing less work. It would be a nice point to decide whether this 

 latter change is also an adaptation. If so it is one in a some- 

 what different sense from that usually employed. The result 

 is of no direct advantage to the animal, except possibly in sav- 

 ing a certain amount of food, but since the same change will 

 take place when an abundance of food is consumed, the result 

 is, under these conditions, of no use. 



The thickening of the skin on those parts of the body where 

 continued pressure is brought to bear on it is a change in a 

 useful direction. The thickening on the soles of the feet and 



