212 EVOLUTION AND GENETICS 



bacteria, and fungi. The green plants make other forms of life 

 possible. Thus the organism as a whole is related to an inorganic 

 and an organic environment, but within itself there are related 

 parts which show that we must consider further an internal en- 

 vironment of any organ. Many organs, indeed, respond only to 

 stimuH from this internal environment, and are reached directly 

 from without only by accident, if at all. To all of these phases of 

 environment the organ or organism must be adjusted if it is to 

 live successfully. Lines of demarcation are not necessarily sharp 

 for an organ may be effective in more than one way. It is possible, 

 however, to note definite adaptations to definite conditions in all 

 organisms. 



Non-Adaptive Characters. Following the publication of Dar- 

 win's Origin of Species there was a marked tendency among scien- 



FiG. 123. — Skull of woodcliuek, showing an upper incisor that had grown in 

 an arc of a circle until it entered the roof of the mouth, after the opposing 

 lower incisor had been broken off. (From Reese's Economic Zoology, with 

 the permission of P. Blakiston's Son and Company.) 



tists to seek and describe marvellous adaptations. It is not sur- 

 prising that this should have occurred, since Darwin showed how 

 wonderfully species are associated with their environments and 

 how important the usefulness of adaptations may be, but the ten- 

 dency to regard any character as adaptive to the external environ- 

 ment must be regarded as extreme. 



We now recognize that an organism may possess many char- 

 acters which cannot be construed as having any value in meeting 

 the conditions of adaptation. Such characters have been called 

 non-adaptive, and it is evident that organisms are made up of 



