NATURAL SELECTION 179 



Strongly that he was led to suppose that new and 

 simple forms are continually being produced by spon- 

 taneous 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 necessarilj^ include progressive 

 development— it only takes advantage of such variations 

 as arise and are beneficial to each creature under its 

 complex relations of life. And it may be asked what 

 advantage, as far as we can see, would it be to an 

 infusorian animalcule — to an intestinal worm — or even 

 to an earthworm, to be highly organized. If it were 

 no advantage, these forms would be left, by natural se- 

 lection, unimproved or but little improved, and might 

 remain for indefinite ages in their present lowly con- 

 dition. And geology tells us that some of the lowest 

 forms, as the infusoria and rhizopods, have remained for 

 an enormous period in nearly their present state. But to 

 suppose that most of the many now existing 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 coexistence 

 of mammals and fish — among mammalia, to the coexist- 

 ence of man and the ornithorhynchus — among fishes, to 

 the coexistence of the shark and the lancelet (Amphi- 

 oxus), which latter fish in the extreme simplicity of its 



