CHAPTER VII 



THE SPECIES 



The species has its origin in the concept of similarity. We 

 say that organisms are similar which are not quite alike but 

 are just distinguishable from one another in a certain respect. 

 If several organisms are to be studied with reference to their 

 similarity, we choose out a special individual as a sample, 

 and compare with it those nearest to it. Then we go on to 

 determine everywhere the just perceptible differences, and 

 in this way we unite together the whole group of organisms. 

 When that is done, the group appears to us as a continuity, 

 which we call " species." 



Within each species we shall always find an individual 

 which lies midway in regard to the total of all the deviations. 

 We call this the " typical case," while those individuals most 

 remote from it in any direction are called " extreme cases." 



It is not at once obvious whether a species is a product of 

 Nature, or whether it is to be considered merely as a means 

 of classifying. But after it had been shown that all living 

 things can be combined into continuous groups or species, 

 and that these are separated from one another by larger 

 gaps, men believed that they were justified in inter- 

 preting species as special products of Creation, whereas 

 the individual " variations " within the species could change 

 in the course of ages. 



It was natural to go on to suppose that, in the course of 

 ages, individual variations might drop out, and, as a result, 

 the originally coherent species would cease to appear con- 



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