u INSENSIBLE VARIATION 65 



culable in number, have ever occurred in the same order 

 on two independent lines of evolution, if they were purely 

 accidental? And how could they have been preserved 

 by selection and accumulated in both cases, the same in 

 the same order, when each of them, taken separately, 

 was of no use? 



Let us turn, then, to the hypothesis of sudden varia- 

 tions, and see whether it will solve the problem. It cer- 

 tainly 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 understanding 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 some- 

 what reduced, but I can also understand better how each 

 could be preserved and added to the others; for the ele- 

 mentary 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 infinitesi- 

 mal. The parts must then all change at once, each con- 

 sulting the others. I agree that a great number of un- 

 coordinated variations may indeed have arisen in less 

 fortunate individuals, that natural selection may have 

 eliminated these, and that only the combination fit to 



