CHAPTER VIII 



ILLUSTRATIVE CASES OF NATURAL SELECTION AND 



ADAPTATION 



We have now learnt something of the great features of the 

 " world of life " whose origin, development, and meaning 

 we are seeking to comprehend ; we have been enabled to 

 visualise its enormous extent, its almost endless diversity of 

 form, structure, and mode of existence ; the vast population of 

 the species that compose it, especially those which we term 

 common. Further, we have seen something of the way in which 

 large numbers of species inhabit the same area intermingled 

 together, which they are enabled to do by each being adapted 

 to some one station or particular kind of food which its 

 peculiar organisation enables it to utilise ; each occupying, as 

 it were, a special place in the economy of nature. 



We have also learnt something of the three great factors 

 which are essential for the gradual modification of species 

 into new and better adapted organisms — heredity, variation, 

 and enormous powers of increase, leading inevitably to a 

 struggle for existence, since of the many that are born only 

 a few can possibly survive. We are, therefore, now prepared 

 to examine, so far as we are able, the exact method of Nature's 

 work in species-production. 



One of the difficulties in the way of an acceptance of 

 continuous evolution through variation and natural selection 

 is, that though variation may be fully admitted, and though 

 great changes of climate and some changes of land and sea 

 have occurred in the human period, these do not seem to 

 have led to the formation of new species, but only to the 

 extinction, or change in the distribution, of a few of them. 

 But of late years naturalists, having pretty well exhausted 



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