CHARLES DARWIN 237 



If we take as the standard of high organisation, the amount of 

 differentiation and specialisation 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 towards this 

 standard ; for all physiologists admit that the specialisation 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 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 organisation. Whether 

 organisation on the whole has actually advanced from the remotest 

 geological periods to the present day will be more conveniently dis- 

 cussed 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 

 towards perfection in all organic beings, seems to have felt this dif- 

 ficulty 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 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 in- 

 fusorian animalcule — to an intestinal worm — or even to an earth- 

 worm, to be highly organised. 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 



