2 THE PROBLEM OF SPECIES. [ixtrod. 



problem of Species. Obscurity has been brought into the treat- 

 ment of the question through want of recognition of the fact that 

 this is really only a part of the general problem, which would still 

 remain if there were only one species. Nevertheless the problem 

 of Species is so tangible a part of the whole that it is perhaps the 

 best point of departure. For our present purpose we cannot 

 begin better than by stating it concisely. 



The forms of living things are diverse. They may neverthe- 

 less be separated into Specific Groups or Species, the members of 

 each such group being nearly alike, while they are less like the 

 members of any other Specific Group. [The Specific Groups may 

 by their degrees of resemblance be arranged in Generic Groups 

 and so on.] 



The individuals of each Specific Group, though alike, are not 

 identical in form, but exhibit differences, and in these differences 

 they may even more or less nearly approach the form characteristic 

 of another Specific Group. It is true, besides, that in the case of 

 many Specific Groups which have been separated from each other, 

 intermediate forms are found which form a continuous series of 

 gradations, passing insensibly from the form characteristic of one 

 Species to that characteristic of another. In such cases the 

 distinction between the two groups for purposes of classification is 

 not retained. 



The fact that in certain cases there are forms transitional 

 between groups which are sufficiently different to have been 

 thought to be distinct, is a very important fact which must not 

 be lost sight of; but though now a good many such cases are 

 known, it remains none the less true that at a given point of 

 time, the forms of living things may be arranged in Specific 

 Groups, and that between the immense majority of these there 

 are no transitional forms. There are therefore between these 

 Specific Groups differences which are Specific. 



No definition of a Specific Difference has been found, perhaps 

 because these Differences are indefinite and hence not capable of 

 definition. But the forms of living things, taken at a given 

 moment, do nevertheless most certainly form a discontinuous 

 series and not a continuous series. This is true of the world as 

 we see it now, and there is no good reason for thinking that it has 

 ever been otherwise. So much is being said of the mutability of 

 species that this, which is the central fact of Natural History, is 

 almost lost sight of, but if ever the problem is to be solved this 

 fact must be boldly faced. There is nothing to be gained by 

 shirking or trying to forget it. 



The existence, then, of Specific Differences is one of the 

 characteristics of the forms of living things. This is no merely 

 subjective conception, but an objective, tangible fact. This is the 

 first part of the problem. 



