26o ESSENTIALS OF BIOLOGY 



fabrication of nests and burrows by many animals ; building 

 houses, ships, etc., by man ; the operations of artisans, musicians, 

 surgeons etc. ; 



The increase in size and efficiency of muscles that are much 

 used (as by blacksmiths, pianists, etc.) ; increased heart-power by 

 athletes ; repairs of bodily injuries carried out by doctors ; plastic 

 surgery ; 



Increased physique and better health of children due to im- 

 proved food, sanitation, clothing, etc. ; 



All education and art. 



These examples illustrate adaptations and they will be sufficient 

 to indicate what are the general characteristics of such changes. 

 It is to be noted that few of them apply to organisms living in 

 wild nature and that they mostly refer to cases where some 

 kind of human control or interference has occurred. In the 

 present phase of the investigation of transformism this experi- 

 mental method is necessary and for a time the methods of the 

 laboratory must be applied. Nevertheless, it must be noted that 

 it is the evolutionary career which we are studying ; that trans- 

 formism has occurred in the past independently of human inter- 

 ference and control and that whatever explanation we make as 

 to the details of the process must be based on naturalistic observa- 

 tions — those of the scientific man who is solely a spectator and 

 not an experimentalist. Meanwhile, of course, the laboratory 

 methods are fashionable, and indeed indispensable. 



The examples show, however, that an adaptation (i) is not 

 merely a passive change undergone by an organism. We must 

 not think of an organic adaptation as being illustrated (as the 

 term suggests) by, say, melted typemetal adapting itself to the 

 form of its environment, that is, to the mould into which it is 

 poured. (2) It is an active response on the part of the organism 

 to something in its natural surroundings : the muscle that is 

 used to a higher degree than the ordinary, as in the case of the 

 athlete's heart, increases in size and efficiency, or a part of the 

 epidermis may thicken so as to resist the increased friction which 

 exceptional activity sets up. (3) There is a specialization of some 

 kind in the relation between the animal and some things in its 

 environment which have particular significance. (4) This relation 

 of specialization is made by the animal itself. 



Mutilations. These are acquirements — changes of structure, 



