CHAPTER III. 



THE CO-EXISTEXCE OF CLOSELY SIMILAR STRUCTURES 

 OF DIVERSE ORIGIN. 



Chances against concordant variations. Examples of discordant ones. 

 Concordant variations not unlikely on a non-Darwinian evolutionary 

 hypothesis. Placental and implacental mammals. Birds and reptiles. 

 Independent origins of similar sense organs. The ear. The eye. 

 Other coincidences. Causes besides "Natural Selection" produce con- 

 cordant variations, in certain geographical regions. Causes besides 

 "Natural Selection" produce concordant variations, in certain zoological 

 and botanical groups. There are homologous parts not genetically 

 related. Harmony in respect of the organic and inorganic worlds. 

 Summary and conclusion. 



THE theory of " Natural Selection" supposes that the varied 

 forms and structure of animals and plants have been built 

 up merely by indefinite, fortuitous, 1 minute variations in 

 every part and in all directions those variations only 

 being preserved which are directly or indirectly useful to 

 the individual possessing them, or necessarily correlated 

 with such useful variations. 



On this theory the chances are almost infinitely great 

 against the independent accidental occurrence and preser- 

 vation of two similar series of minute variations resulting 



o 



1 By accidental variations Mr. Darwin does not, of course, mean to 

 imply variations really due to "chance," but to utterly indeterminate 

 antecedents. 



