152 ON THE DEGREE TO WHICH [Chap. IV, 



state as I should be inclined to add, and their specialisa- 

 tion for different functions; or, as Milne Edwards would 

 express it, the completeness of the division of physio- 

 logical labour. But we shall see how obscure this sub- 

 ject 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 niost from the other vertebrate classes. We 

 see still more plainly the obscurity of the subject by 

 turning to plants, amongst which the standard of intel- 

 lect 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 specialieation of the sev- 

 eral organs in each being when adult (and this will in- 

 clude the advancement of the brain for intellectual pur- 

 poses), natural selection clearly leads towards this 

 standard: for all physiologists admit that the speciali- 

 sation of organs, inasmuch as in this state they perform 

 their functions better, is an advantage to each being; 

 and hence the accumulation of variations tending 

 towards specialisation is within the scope of natural se- 

 lection. 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 occu- 

 pied place in the economy of nature, that it is quite pos- 

 sible for natural selection gradually to fit a being to a 



