CHAPTER X 

 SUMMARY 



Adaptation Stimuli to growth The confusion as to what is innate and 

 what is acquired Variations Spontaneous variability and insusceptibility of 

 the germ-plasm Recapitulation The function of conjugation Blending 

 Alternative recapitulation Fluctuations and mutations The difficulties pre- 

 sented by the different sciences Methods of inquiry The method of comparing 

 races Materials supplied by human beings The greater problems of Heredity. 



338. "lt~lf 7"E see then that the great outstanding feature of living 

 beings is that, in part and whole, they are adapta- 

 tions. For example, in man, the being we know 

 best, very few characters exist the utility of which in past or present 

 has not already been ascertained. Doubtless a proportion of his 

 characters for instance susceptibility to the charm of alcohol 

 may be mere by-products of evolution, accidental accompaniments 

 of useful characters ; but, speaking comparatively, they are rare. 

 His nervous, circulatory, muscular, glandular, digestive, and other 

 systems, the mass of his characters, his specific and varietal 

 traits as distinguished from his personal variations, are nearly 

 all demonstrably useful. We shall see that what is true of his body 

 is true also of his mind. The variations of the individual are, of 

 course, not all useful, but the spontaneous variability to which they 

 are due and which supplies the materials for selection is an 

 immensely useful trait which has been evolved through Natural 

 Selection into an adaptation. Presumably adaptation is not less 

 perfect in plants and lower animals than in man. Apparently they 

 have been just as much subjected to selection. In all probability, 

 therefore, if we are less able to trace the utility of all their 

 characters, it is only because here our knowledge is less complete. 

 It must be borne in mind, however, that nature can do no more 

 than choose from the variations or combinations of variations that 

 happen to be presented to her for selection. If, therefore, two 

 sections of a species separated, but continued to exist under 

 conditions which (were it possible) were identical, they would still 

 be sure to differentiate ; for neither the variations presented to 

 nature for selection nor the accidents of survival would be quite 



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