CHAPTER VI 



THE NUMERICAL DISTRIBUTION OF SPECIES IN 

 RELATION TO EVOLUTION 



The rather lengthy account I have given of the numerical 

 distribution of species over both small and large areas, 

 and in special relation to latitude and to climate, has a 

 very definite object. In the first place, this distribution 

 constitutes the primary and fundamental fact in the relation 

 of species to the whole environment — it is, in fact, the 

 broadest and most simple expression of that relation, and 

 is thus a proper subject of inquiry in any general view 

 of the world of life. Yet it has been strangely neglected 

 both by botanical and zoological writers ; and the largest 

 and oldest collections of plants and animals in all countries 

 have been so dealt with as to afford material for almost every 

 form of biological research except this one. 



The mere enumeration of the numbers of species, named 

 or unnamed, with the localities of each specimen, in the great 

 national collections of the world, would have afforded all the 

 materials for such comparisons as I have here endeavoured to 

 make. And if the facts were recorded in card-catalogues, 

 instead of in the usual forms, there would be such a demand 

 for sets of these cards applying to special groups and 

 definite geographical areas, by most students or collectors, 

 that the cost of such catalogues would be more than repaid. 



This numerical relation of the various groups of organisms 

 in different areas or geographical divisions of the earth 

 has the further advantage of being interesting and intelligible 

 to the general reader, as it involves the use of hardly any 

 technical terms, and is therefore especially suitable for a 



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