LECTURE II 

 THE MECHANISM OF ADAPTATION 



THE wonderful adaptations of organisms to their en- 

 vironments, of structures to habits, of responses to 

 needs, of means to ends, have ever been and still are the 

 greatest problems of biology. From the time of the early 

 Greek philosophers to the present day, the mystery of life 

 has centered to a large extent in this great problem of how 

 organisms came to be so marvelously adapted, in structures 

 and functions, for their preservation and welfare. Aristotle 

 maintained that the essence of a living thing is its fitness, 

 and after centuries of observation, experiment, and theoriz- 

 ing we must still say that one of the most mysterious and 

 inexplicable phenomena in nature is the capacity of the 

 lowest plants and animals, as well as of the highest, to re- 

 spond to external conditions and stimuli in a useful and an 

 apparently intelligent and purposive way, although it is 

 certain that conscious intelligence and purpose are not usu- 

 ally involved. 



How have lowly organisms learned to utilize processes 

 of chemistry and physics so subtle in character that intelli- 

 gent man after centuries of civilization has come only 

 to the place where he can appreciate these processes but 

 cannot duplicate them? How have those units of living 

 matter, the cells, come to have complex ideological mechan- 

 isms for assimilation, growth, and division, for secretion, 

 contraction, and sensation? How can we explain the origin 

 of multitudes of inheritance units, their location in the 

 chromosomes, the wonderful mechanism of mitosis for the 

 precise division and distribution of these chromosomes to all 



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