152 ON THE DEGKEE TO WHICH [Chap. IV. 



should be inclined to add, and their specialisation for 

 different functions ; or, as Milne Edwards would express 

 it, the completeness of the division of physiological 

 labour. But we shall see how obscure this subject is if 

 we look, for instance, to fishes, amongst which some 

 naturalists rank those as highest which, like the sharks, 

 approach nearest to amphibians ; whilst other naturalists 

 rank the common bony or teleostean fishes as the highest, 

 inasmuch as they are most strictly fish-like, and differ 

 most from the other vertebrate classes. We see still 

 more plainly the obscurity of the subject by turning to 

 plants, amongst which the standard of intellect is of 

 course quite excluded; and here some botanists rank 

 those plants as highest which have every organ, as sepals, 

 petals, stamens, and pistils, fully developed in each 

 flower; whereas other botanists, probably with more 

 truth, look at the plants which have their several organs 

 much modified and reduced in number as the highest. 



If we take as the standard of high organisation, the 

 amount of differentiation and specialisation of the several 

 organs in each being when adult (and this will include 

 the advancement of the brain for intellectual purposes), 

 natural selection clearly leads towards this standard: 

 for all physiologists admit that the specialisation of 

 organs, inasmuch as in this state they perform their func- 

 tions better, is an advantage to each being ; and hence the 

 accumulation of variations tending towards specialisation 

 is within the scope of natural selection. On the other 

 hand, we can see, bearing; in mind that all organic beings 

 are striving to increase at a high ratio and to seize on 

 every unoccupied or less well occupied place in the 

 economy of nature, that it is quite possible for natural 

 selection gradually to fit a being to a situation in which 



