i SUDDEN VARIATION 69 



It certainly lessens the difficulty on one point, but it 

 makes it much worse on another. If the eye of the 

 mollusc and that of the vertebrate have both been 

 raised to their present form by a relatively small number 

 of sudden leaps, I have less difficulty in understand 

 ing the resemblance of the two organs than if this 

 resemblance were due to an incalculable number of 

 infinitesimal resemblances acquired successively : in 

 both cases it is chance that operates, but in the second 

 case chance is not required to work the miracle it 

 would have to perform in the first. Not only is 

 the number of resemblances to be added somewhat 

 reduced, but I can also understand better how each 

 could be preserved and added to the others ; for the 

 elementary variation is now considerable enough to be 

 an advantage to the living being, and so to lend itself 

 to the play of selection. But here there arises another 

 problem, no less formidable, viz., how do all the parts 

 of the visual apparatus, suddenly changed, remain so 

 well coordinated that the eye continues to exercise 

 its function ? For the change of one part alone will 

 make vision impossible, unless this change is absolutely 

 infinitesimal. The parts must then all change at once, 

 each consulting the others. I agree that a great 

 number of uncoordinated variations may indeed have 

 arisen in less fortunate individuals, that natural selec 

 tion may have eliminated these, and that only the 

 combination fit to endure, capable of preserving and 

 improving vision, has survived. Still, this combina 

 tion had to be produced. And, supposing chance to 

 have granted this favour once, can we admit that it 

 repeats the self-same favour in the course of the history 

 of a species, so as to give rise, every time, all at once, to 

 new complications marvellously regulated with reference 



