CHAPTER III. 



THE CO-EXTSTEXCE OF CLOSELY SIMILAR STRUCTURES 



OF DIVERSE ORIGIN. 



Cliauces against concordant variations. — Examples of discordant ones. — 

 Concordant variations not unlikely on a non-Darwinian evolutionary 

 hypothesis. — ^Placental and im])lacental mammals. — Birds and reptiles. 

 — Independent origins of simihir sense organs. — The ear. — The eye. — 

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

 cordant variations, in certain geograjihical regions. — Causes besides 

 " Xatural 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 " Xatural Selection" supposes that the varied 

 forms and structure of animals and plants have been built 

 up merely by indefinite, fortuitous/ 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 

 vith 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 resultinir 



o 



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

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

 antecedents. 



