EVOLUTION AND NATURAL SELECTION 19 



Johannsen steps in, analyzing more completely this result of 

 breeding from the extremes of the frequency polygon.^ 



"The fundamental principle of Johannsen is that an ordinary 

 frequency polygon is usually made up of measurements of a 

 characteristic belonging to a non-homogeneous mass of indi- 

 viduals; that it is really analyzable into several elementary 

 masses each of which has a frequency polygon of its own. 

 In each elementary polygon the variation is strictly due to 

 non-inheritable somatic modifications, selection of extremes of 

 which has no genetic significance. But the selection for 

 breeding of individuals belonging to different elementary 

 polygons, lying, say, at the extremes of the complex, may 

 quickly lead to an isolation of these elementary polygons, the 

 constituent individuals of which reproduce their pecuharities 

 as distinct elementary species. Thus Johannsen holds that 

 not only do individuals with quahtatively dissimilar characters 

 belong to distinct elementary species, but often such as are 

 only quantitatively unUke. The complex variation-groups are 

 called by the author phaenotypes, or false types, the elementary 

 variation-groups are genotypes, or genetic types." 



Utility and Natural Selection 



Perhaps no principle has created more discussion than that 

 which Darwin so earnestly impressed upon us, namely : that no 

 special organs, no characteristic form of markings, no peculiari- 

 ties of instinct or habit, no relation between species or races 

 can exist but must now be, or at a previous time have been, 

 useful to the individual or species which possesses them. 

 Natural selection cannot possibly prodilce any modification 

 exclusively for the good of another species, although they 

 often take advantage of beneficial structures. Darwin also 

 maintained that if it could be proved that any part of the 

 structure of any one species had been formed for the ex- 

 clusive good of another species, it would annihilate his 

 theory, for such could not have been produced by natural 

 selection. Wallace tells of the varied ways in which the 

 coloring and form of animals serve for their protection, 



'For further study of so-called frequency polygon consult "Davenport's 

 Methods," second ed., 1904. 



