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 visualize 

 its enormous extent, its almost endless diversity of form, struc- 

 ture, 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 to- 

 gether, 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 enor- 

 mous 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 exam- 

 ine, 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 con- 

 tinuous 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 foraiation 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 the well-defined 

 species of the best-known parts of the world — Europe and 



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