100 THE ORIGIN OF SPECIES 



among which some naturalists rank those as highest which, like 

 the sharks, approach nearest to amphibians; while other natural- 

 ists rank the common bony or teleostean fishes as the highest, inas- 

 much 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 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 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 speciali- 

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

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

 mulation 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 selec- 

 tion 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 organization. Whether organization 

 on the whole has actually advanced from the remotest geological 

 periods to the present day, will be more conveniently discussed in 

 our chapter on Geological Succession. 



But it may be objected that if all organic beings thus tend to 

 rise in the scale, how is it that throughout the world a multitude 

 of the lowest forms still exist; and how is it that in each great 

 class some forms are far more highly developed than others? Why 

 have not the more highly developed forms everywhere supplanted 

 and exterminated the lower? Lamarck, who believed in an innate 

 and inevitable tendency toward perfection in all organic beings, 

 seems to have felt this difficulty so strongly that he was led to sup- 

 pose that new and simple forms are continually being produced by 

 spontaneous generation. Science has not as yet proved the truth of 

 this belief, whatever the future may reveal. On our theory the con- 

 tinued existence of lowly organisms offers no difficulty; for natural 

 selection, or the survival of the fittest, does not necessarily include 



