OBJECTIONS TO THE THEORY OF DESCENT. 313 



areas have been in some respects highly favorable for the 

 production of new species, yet that the course of modifi- 

 cation will generally have been more rapid on large areas ; 

 and what is more important, that the new forms produced 

 on large areas, which already have been victorious over 

 many competitors, will be those that will spread most 

 widely, and will give rise to the greatest number of new 

 varieties and species. They will thus play a more impor- 

 tant part in the changing history of the organic world. 



WHY THE HIGHER FORMS HAVE NOT SUPPLANTED THE 

 LOWER. 



Ori«nn of But ^ mSL J be objected that if all organic 



Species, beings thus tend to rise in the scale, how is it 

 page " that throughout the world a multitude of the 

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

 clas3 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 tend- 

 ency 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 

 progressive development — it only takes advantage of such 

 variations as arise and are beneficial to each creature 

 under it3 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 



