222 



SELECTION. 



Chap. XX. 





present perfect type. By small and doubtful steps sucli as these 

 nature, as we may confidently believe, has progressed on her 

 grand march of improvement and development. 



A similar line of reasoning is as applicable to separate organs 

 as to the whole organisation. A writer 91 has recently maintained 

 that " it is probably no exaggeration to suppose that, in order to 



a 



improve such an organ as the eye at all, it must be improved 



" in ten different ways at once. And the improbability of any 

 " complex organ being produced and brought to perfection in 

 " any such way is an improbability of the same kind and degree 

 " as that of producing a poem or a mathematical demonstration 

 " by throwing letters at random on a table." If the eye were 

 abruptly and greatly modified, no doubt many parts would have 

 to be simultaneously altered, in order that the organ should 

 remain serviceable. # 



But is this the case with smaller changes? There 

 persons who can see distinctly only in a dull light, and 



are 



condition depends, I believe 



the abnormal 



of 



the 



and 



known to be inherited. Now, if a bird, for 



eceived some great advantage from seeing well in 



ght, all the individuals with the most 



ould succeed best and be the most likely 



and why 



blend their respective advantag 



should not all those which happened to have the eye itself a 

 little larger, or the pupil capable of greater dilatation, be likewise 

 preserved, whether or not these modifications were strictly simul- 

 taneous ? These individuals would subsequently intercross and 



is. By such slight successive 

 changes, the eye of a diurnal bird would be brought into the 

 condition of that of an owl, which has often been advanced as 

 an excellent instance of adaptation. Short-sight, which is often 

 inherited, permits a person to see distinctly a minute object at so 

 near a distance that it would be indistinct to ordinary eyes ; and 

 here we have a capacity which might be serviceable under cer- 



tain conditions, abruptly gained. The Fueg 



board 



91 Mr. J. J. Murphy in his opening given by the Rev. 0. Pritchard, Pres. 



address to the Belfast Nat. Hist. Soc., Royal Astronomical Soc, in his sermon 



as given in the Belfast Northern Whig, (Appendix, p. 33) preached before the 



Nov. 19, 1866. Mr. Murphy here fol- British Association at Nottingham, 



lows the line of argument against my 1866. 

 views previously and more cautiously 





V 



) 



. 



