CHAPTER XVIII. 

 GEOLOGY AND THE CONSTANCY OF SPECIES. 



The selection-theory, as well as the theories based on 

 inheritance of acquired characters, must suppose that 

 variability, will it have any effect, must occur more or 

 less continuously, that in other words organisms can 't 

 survive very long without showing variation. It is even 

 inconceivable, on the ground of these theories, that the 

 groups considered by them to be primitive, say like the 

 Flagellates, should yet remain in existence, notwith- 

 standing aU the changes which the earth has imder- 

 gone must have been inductive to their var5dng. This 

 applies even, though in a lesser degree, to the mutation 

 theory, the only conception able to explain the unchan- 

 ged continuation of a homozygotic type through long 

 ages, is the conception that a species is constant, unless 

 it happens to cross with another one. 



Now what does the geoloigcal record teach us to 

 this effect? Let us quote here what Grand' Euey than 

 whom no one, has greater experience in this matter, 

 says: 



„Unfait notoire domine tous les autres, la permanence 

 „des espices durant la majorite ou la presque totaliU de 

 leur „existence". 



Venn il y a 25 ans k St. Etienne avec I'id^e contraire 

 que les especes ont vari6 d'une maniere continue, D. 



