OROANIZA TlOJSr TENDS TO AD VANCE. 1 1 7 



which several parts of the structure become less perfect, so 

 that the mature animal cannot be called liiglier tliau its 

 larva. Von Baer's standard seems the most widely appli- 

 cable and the best, namely, the amount of differentiation of 

 the parts of the same organic being, in the adult state, as I 

 should be inclined to add, and their specialization for 

 different functions; or, as Milne Edwards would express it, 

 the completeness of the division of physiological labor. 

 But we shall see how obscure this subject is if we look, for 

 instance, to fishes, among which some naturalists rank 

 those as highest which, like the sharks, approach nearest 

 to amphibians; while 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, among which the 

 standard of intellect is of course quite excluded; and here 

 some botanists rank those plants as highest which have 

 every organ, as sepels, petals, stamens and pistils, fully 

 developed in each flower; whereas other botanists, probably 

 with more truth, look at the plants v/hich have their 

 several organs much modified and reduced in number as 

 the highest. 



If we take as the standard of high organization, the 

 amount of differentiation and specialization 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 toward this standard: for 

 all physiologists admit that the specialization 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 toward specialization 

 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 

 several organs would be superfluous or useless: in such 

 cases there would be retrogression in the scale of organiza- 

 tion. Whether organization on the whole has actually ad- 

 vanced from the remotest geological periods to the present 



