300 Problems of Organic Adaptation 



Such special adaptations to particular conditions of life 

 are very common among all organisms, but they are not 

 universal. Some organisms have been able to adjust them- 

 selves to one kind of environment and others to another 

 kind, and although a certain degree of adaptability is uni- 

 versally present, no single organism is able to adjust itself 

 to every kind of environment. Special adaptations to par- 

 ticular conditions of life are examples of differentiation, 

 which always implies limitations in certain directions in 

 order to progress in other directions. Consequently one 

 organism is peculiarly fitted for one environment and 

 another for another, but no organism is universally fitted 

 for all environments. 



Again, adaptations are relative but not absolute adjust- 

 ments. Even the most perfect adaptation is not absolutely 

 perfect. For example, that marvel of adaptation, the human 

 eye, is very far from being a perfect optical instrument; 

 Helmholtz is reported to have said that if an optician 

 should send him an optical instrument as imperfect as the 

 human eye, he would send it back to him and tell him to 

 learn his business; and yet there is probably no more perfect 

 adaptation in nature than this. Furthermore, all grada- 

 tions of adjustment occur among different organisms from 

 the relatively imperfect to the most perfect, and these 

 gradations indicate that fitness in the living world is rela- 

 tive and not absolute, and they indicate that adaptations 

 are a product of natural evolution rather than of super- 

 natural creation. 



Adaptations to particular conditions of life are seen in 

 almost every structure, function, and relation of organisms ; 

 in the microscopic and ultra-microscopic parts of cells, as 

 well as in entire cells, tissues, organs, systems, biological 

 persons, and animal states; in the chemical and physical 



