210 THE POPULAR SCIENCE MONTHLY. 



tion ; and they are still more distinctly opposed to any view which 

 should lead to the belief that the modification in different types of 

 animal or vegetable life goes on equally and evenly. The facts, as I 

 have placed them before you, would obviously contradict directly any 

 such form of the hypothesis of evolution as laid clown in these two 

 postulates. 



Now, the service that has been rendered by Mr. Darwin in the 

 doctrine of evolution in general is this : that he has shown that there 

 are two great factors in the process of evolution : one of them is the 

 tendency to vary, the existence of which may be proved by observa- 

 tion in all living forms; the other is the influence of surrounding 

 conditions upon what I may call the parent form and the variations 

 which are thus evolved from it. The cause of the production of vari- 

 ations is a matter not at all properly understood at present. Whether 

 it depends upon some intricate machinery if I may use the phrase 

 of the animal form itself, or whether it arises through the influence 

 of conditions upon that form, is not certain, and the question may for 

 the present be left open. But the important point is the tendency to 

 the production of variations ; then, whether the variations which are 

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

 form shall survive and supplant the variations, is a matter which 

 depends entirely on surrounding conditions. If the surrounding con- 

 ditions are such that the parent form is more competent to deal with 

 them and flourish in them than the derived forms, then, in the strug- 

 gle 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 better for the derived than for 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 advance of type, 

 through any imaginable series of ages ; in the second place, there 

 will be modification and change of form. Thus the existence of these 

 persistent types of life is no obstacle in the way of the theory of evo- 

 lution at all. Take the case of the scorpions to which I have just 

 referred. No doubt, since the Carboniferous epoch conditions have 

 existed such as existed when the scorpions of that epoch flourished, 

 in which they find themselves better off, more competent to deal with 

 the difficulties in their way than any kind of variation from the scor- 

 pion type ; and for that reason the scorpion has persisted, and has not 

 been supplanted by any other form. And there is no reason in the 

 nature of things why, as long as this world exists, if there be condi- 

 tions more favorable to scorpions than any variation which may arise 

 from them, these forms of life should not persist. 



Therefore, this objection is no objection at all. The facts of this 

 character and they are numerous belong to that class of evidence 

 which I have called indifferent. That is to say, they may afford no 



