7G THE GKNESIS OF SPKCIKS. '[Chap. 



CHAPTER III. 



THE COEXISTENCE OF CLOSELY-SIMILAR STRUCTURES OF 



DIVERSE ORIGIN. 



Chances apninst Concordant Vurliitlons. — Examples of Discordant Oiu-s. — ('oncordant 

 Variations not unlikely on a non-Darwinian Evolutionary Hypothesis. — I'Licental 

 and InipLicentjil Mammals. — IJirds and lieptiles. — Indei)endent Ori{,'in3 of Similar 

 Sense Organs. — The Ear. — The Eye. — Other Coincidences. — Causes besides Natural 

 Selection produco Concordant Variations in Certain CJeograiihluil Ket,'ion8.— ('auses 

 besides Natural Selection i)roduco Concordant Variations in ('erUtin Zooloj^'icul and 

 IJotauical Ci-oups. — There aru Homologous Parts not geiietlwilly related. — Harmony 

 la respect of the Organic and Inorganic "Worlds. — Sumuioiy and Conclusion. 



The theory of " Natural Selection " supposes that tlie 

 varied forms and structure of animals and j)lants have been 

 built up merely hy indefinite, fortuitous,* minute variations 

 in everj' part and in all directions — those variations only 

 being j)reserved which are directly or indirectly usefid to 

 tlie 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 pres- 

 ervation of two similar series of minute variations result- 

 ing in the independent development of two closely-similar 

 forms. In all cases, no doubt (on this same theory), sotne 

 adaptation to habit or need would gradually be evolved, 

 but that adaptation would surely be arrived at by dillerent 

 roads. The organic world su])plies us with multitutles of 



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

 imply variatioua really due to " chance," bai to utterly indctcrmiuate 

 antecedents. 



