6 METHODS OF ATTACKING THE PROBLEM. [introd. 



are apparently identical live under conditions which are apparently 

 very different, while species which though closely allied are con- 

 stantly distinct are found under conditions which are apparently 

 the same. If we would make these facts accord with the view 

 that it is diversity of environment which is the measure of 

 diversity of specific form, it is necessary to suppose either (1) 

 that our estimate of similarity of forms, or of environment, is 

 wholly untrustworthy, or else (2) that there is a wide area of 

 environmental or structural divergence within which no sensible 

 result is produced : that is to say, that the relation between en- 

 vironment and structure is not finely adjusted. But either of these 

 admissions is serious ; for if we grant the former we abrogate the 

 right of judgment, and are granting that our proposed solutions 

 are mere hypotheses which we have no power to test, while if we 

 admit the latter, we admit that environment cannot so far be either 

 the directing cause or the limiting cause of Specific Differences, 

 though the first is essential to Lamarck's Theory, and the second is 

 demanded by the doctrine of Natural Selection. 



Such then, put very briefly, are the two great theories, and this 

 is one of the chief difficulties which beset them. We must now 

 pass to our proper work. 



We have to consider whether it is not possible to get beyond 

 the present position and to penetrate further into this mystery 

 of Specific Forms. The main obstacle being our own ignorance, 

 the first question to be settled is what kind of knowledge would 

 be of the most value, and which of the many unknowns may 

 be determined with the greatest profit. To decide this we must 

 return once more to the ground which is common to all the induc- 

 tive theories of Evolution alike. Now all these different theories 

 start from the hypothesis that the different forms of life are re- 

 lated to each other, and that their diversity is due to Variation. 

 On this hypothesis, therefore, Variation, whatever may be its cause, 

 and however it may be limited, is the essential phenomenon of 

 Evolution. Variation, in fact, is Evolution. The readiest way, 

 then, of solving the problem of Evolution is to study the facts of 

 Variation. 



SECTION II. 



Alternative Methods. 



The Study of Variation is therefore suggested as the method 

 which is on the whole more likely than any other to give us the 

 kind of knowledge we are wanting,-. It should be tried not so 

 much in the hope that it will give any great insight into those 



element of discontinuity may thus b3 introduced. This is true, but it does not 

 help in the attempt to find the cause of the original discontinuity of the coexisting 

 organisms. 



