Chap. XX. SELECTION. 207 



could see the long line of ancestors of a first-rate greyhound 

 up to its wild wolf-like progenitor, we sliordd behold an 

 infinite number of the finest gradations, sometimes in one 

 character and sometimes in another, but all leading towards 

 our present perfect type. By small and doubtful steps such 

 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 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 ini- 

 " probability 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 are 

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

 condition depends, I believe, on the abnormal sensitiveness of 

 the retina, and is known to be inherited. Now if a bird, for 

 instance, receive some great advantage from seeing well in 

 the twilight, all the individuals with the most sensitive 

 retina would succeed best and be the most likely to survive ; 

 and why 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 simultaneous ? These individuals would sub- 

 sequently intercross and blend their respective advantages. 

 By such slight successive changes, the eye of a diurnal bird 

 would be brought into the condition of that of an owl, which 



91 Mr. J. J. Murphy, in his opening cautiously given by the Rev. C. 



address to the Belfast Nat. Hist. Soc, Pritchard, Pres. Royal Astronomical 



as given in the ' Belfast Northern Soc, in his sermon (Appendix, p. 33) 



Whig,' Nov. 19, 1866. Mr. Murphy preached before the British Associa 



here follows the line of argument tion at Nottingham, 1*€6. 

 against my views previously and more 



