CHAPTER IV 



BIOLOGICAL EVOLUTION 



Having surveyed in outline the social theories of Comte and 

 Spencer with special reference to their bearing on the doctrine of 

 adaptation, and having reviewed the various methods in use in 

 social science and social philosophy and considered their bearing 

 on our subject, pointing out some of the dangers lurking in the 

 use of the classifying, analogical and statistical methods, our next 

 problem is to study the development of the doctrine of adapta- 

 tion by those who have endeavored to explain evolution in terms 

 of the influence of the environment on the organism or social 

 group. 



The environment may afifect the organism in three different 

 ways: (i) by direct action, producing molecular, chemical or 

 functional changes as in pigmentation and acclimatization; 

 (2) by affording favorable opportunity for growth and functional 

 variation, or the reverse, as in change of habitat resulting in 

 increase or decrease of food, or (3) by furnishing conditions favor- 

 able to struggle and selection. 



The first view, advocated by Buff on and Erasmus Darwin,^ was 

 eclipsed for a long time under the influence of the theory of nat- 

 ural selection but has been upheld firmly by Viet, Scott Elliott, 

 W. H. DaU and others, and still more recently by the advocates of 

 the theory of geographical isolation as the most important factor 

 in species formation.^ 



The direct influence of environment on the organism is well 

 illustrated by the words of Dall though in somewhat exaggerated 

 terms: " The environment stands in a relation to the individual 

 such as the hammer and anvil bear to the blacksmith's hot iron. 

 The organism suffers during its entire existence a continuous 



1 Packard, Lamarck, pp. 203, 218. 



2 Kellogg, Darwinism To-day, ch. IX. 



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