CHAPTER II 



SPECIES THEIK NUMBEKS, VAKIETY, AND DISTRIBUTION 



When we begin to inquire into the main features, the mode 

 of development, the past history, and the probable origin of 

 the great World of Life of which we form a part, which 

 encloses us in its countless ramifications, and upon whose pres- 

 ence in ample quantity we depend for our daily food and 

 continued existence, we have perpetually to discuss and to deal 

 with those entities technically kno^vn as species, but which are 

 ordinarily referred to as soi'ts or kinds of plants and animals. 

 When we ask how many hinds of deer or of thiTishes, of trout 

 or of butterflies, inhabit Britain, w^e mean exactly the same 

 thing as the biologist means by species, though we may not be 

 able to define what we mean so precisely as he does. 



Many people imagine, however, that Darwin's theory proves 

 that there are no such things as species ; but this is a complete 

 misconception, though some biologists use language which 

 seems to support it. To myself, and I believe to most natural- 

 ists, species are quite as real and quite as important as when 

 they were held to be special creations. They are even more 

 important, because they constitute the only definite, easily rec- 

 ogTiised, and easily defined entities which form the starting- 

 point in all rational study of the vast complex of living things. 

 They are now known to be not fixed and immutable as for- 

 merly supposed; yet the great mass of them are stable within 

 very narrow limits, w^hile their changes of form are so slow, 

 that it is only now, after fifty years of continuous search by 

 countless acute observers, that we have been able to discover 

 a very few cases in which a real change — the actual produc- 

 tion of new species — appears to be going on before our eyes. 

 The reader may therefore rest assured that there is no mystery 



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