SOME COMMON ERRORS CONSIDERED 101 



Given the necessary constancy and simplicity of the 

 conditions, the product will remain constant: it will 

 neither regress nor progress, once adequate adapta- 

 tion has been established. Many lowly animal and 

 vegetable forms have persisted unchanged throughout 

 long geological epochs which must have consumed 

 millions of 3 7 ears. These forms have gained com- 

 plete adaptation to their environment, they have 

 not been subject to the action of any of the factors 

 of organic evolution, and therefore they have under- 

 gone no change for ages, and will persist until at 

 last the conditions under which they have so long 

 persisted cease to obtain. This fact of the per- 

 sistence of types is entirely in accordance with 

 evolutionary theory, and affords us no difficulty 

 whatever. But here also our opponents find an 

 opportunity for basing an objection to the theory 

 on their imperfect understanding of it. Forgetful 

 of the immeasurable difference between relative per- 

 sistence — even for millions of years — and absolute 

 persistence — a mistake which is readily intelligible 

 when we remember whence their ideas of a " lono- 

 time " are derived — they point to these long-constant 

 types, and ask us how we propose to reconcile their 

 persistence with what they conceive to be our 

 theory of ceaseless ascent from lower to higher 

 organic forms. The evolutionists are for ever 

 asserting — they say — that species are not immutable ; 

 how then comes it that many species are immut- 

 able ? l But there is a very real difference between 

 the assertion that species may undergo change — if 



1 For "immutable" they should properly say "relatively per- 

 sistent." 



