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THE POPULAR SCIENCE MONTHLY. 



shall survive and supplant the parent, or whether the parent form shall 

 survive and supplant the variations, is a matter which dej^ends entirely 

 on those conditions which give rise to the struggle for existence. If 

 the surrounding conditions are such that the parent form is more com- 

 petent to deal with them and flourish in them than the derived forms, 

 then in the struggle for existence the parent form will maintain itself, 

 and the derived forms will be exterminated. But, if, on the contrary, 

 the conditions are such as to be more favorable to a derived than to 

 the parent form, the parent form will be extirpated, and the derived 

 form will take its place. In the first case, there will be no progression, 

 no change of structure, through any imaginable series of ages ; in the 

 second place, there will be modification and change of form." To 

 the same end Darwin himself leads us. In one or two very pregnant 

 passages, the author of the " Theory of Natural Selection " very plainly 

 indicates why progression should not be universal, and why certain 

 beings remain lowly organized while others attain to the summit and 

 pinnacle of their respective organizations. " How is it," says Darwin, 

 " 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 develoj^ed 

 forms everywhere supplanted and exterminated the lower ? " An- 

 swering his own queries, Darwin says that natural selection by no 



Fig. 8. Pearly Nautilus. 



means includes " progressive development it only takes advantage," 

 he remarks, "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 



