ORGANIZATION TENDS TO ADVANCE. Ill 



present day, will be more conveniently discussed in our chap^ 

 ter 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 inevi- 

 table tendency toward perfection in all organic beings, seems 

 to have felt this difficulty so strongly that he was led to 

 suppose 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 continued existence of lowly 

 organisms offers no difficulty ; for natural selection, or the 

 survival of the fittest, does not necessarily include progres- 

 sive development — it only takes advantage of such varia- 

 tions as arise and are beneficial to each creature under its 

 complex relations of life. And it may be asked what advan- 

 tage, as far as we can see, would it be to an infusorian ani- 

 malcule — to an intestinal worm — or even to an earth-worm, 

 to be highly organized. If it were no advantage, these 

 forms would be left, by natural selection, unimproved or but 

 little improved, and might remain for indefinite ages in 

 their present lowly condition. And geology tells us that 

 some of the lowest forms, as the infusoria and rhizopods, 

 have remained for an enormous period in nearly their pres- 

 ent state. But to suppose that most of the many now exist- 

 ing low forms have not in the least advanced since the first 

 dawn of life would be extremely rash ; for every naturalist 

 who has dissected some of the beings now ranked as very 

 low in the scale, must have been struck with their really 

 wondrous and beautiful organization. 



Nearly the same remarks are applicable, if we look to the 

 different grades of organization within the same great group; 

 for instance, in the vertebrata, to the co-existence of mam- 

 mals and fish — among mammalia, to the co-existence of man 

 and the ornithorhynchus — among fishes, to the co-existence 

 of the shark and the lancelet (Amphioxus), which latter fish 

 in the extreme simplicity of its structure approaches the 

 invertebrate classes. But mammals and fish hardly come 

 into competition with each other ; the advancement of the 

 whole class of mammals, or of certain members in this class. 



