60 CREATIVE EVOLUTION 



this part of the problem, for we are not concerned here 

 with what has perished, we have to do only with what 

 has survived. Now, we see that identical structures 

 have been formed on independent lines of evolution by 

 a gradual accumulation of effects. How can accidental 

 causes, occurring in an accidental order, be supposed 

 to have repeatedly come to the same result, the causes 

 being infinitely numerous and the effect infinitely 

 complicated ? 



The principle of mechanism is that &quot; the same causes 

 produce the same effects.&quot; This principle, of course, 

 does not always imply that the same effects must have 

 the same causes ; but it does involve this consequence 

 in the particular case in which the causes remain visible 

 in the effect that they produce and are indeed its 

 constitutive elements. That two walkers starting from 

 different points and wandering at random should finally 

 meet, is no great wonder. But that, throughout their 

 walk, they should describe two identical curves exactly 

 superposable on each other, is altogether unlikely. The 

 improbability will be the greater, the more complicated 

 the routes ; and it will become impossibility, if the 

 zigzags are infinitely complicated. Now, what is this 

 complexity of zigzags as compared with that of an 

 organ in which thousands of different cells, each being 

 itself a kind of organism, are arranged in a definite 

 order ? 



Let us turn, then, to the other hypothesis, and see 

 how it would solve the problem. Adaptation, it says, 

 is not merely elimination of the unadapted ; it is due 

 to the positive influence of outer conditions that have 

 moulded the organism on their own form. This time, 

 similarity of effects will be explained by similarity of 

 cause. We shall remain, apparently, in pure mechanism. 



