NECESSARY EFFICIENCY OF NATURAL SELECTION. 1 69 



founded, may be perceived even from the outlines of the doc- 

 trine of selection which have just been discussed. Darwin 

 assumes no kind of unknown forces of nature, nor hypothetical 

 conditions, as the acting causes for the transformation of organic 

 forms, but solely and simply the universally recognized vital 

 activities of all organisms, which we term Inheritance and 

 Adaptation. Every naturalist acquainted with physiology 

 knows that these two phenomena are directly connected 

 with the functions of propagation and nutrition, and, like all 

 other phenomena of life, are purely mechanical processes of 

 nature, that is, they depend upon the molecular phenomena 

 of motion in organic matter. That the interaction of these 

 two functions effect a continual, slow transmutation of or- 

 ganic forms, is a necessary result of the struggle for exist- 

 ence. But this, again, is no more a hypothetical relation, nor 

 one requiring a proof, than is the interaction of Inheritance 

 and Adaptation. The struggle for life is a mathematical 

 necessity, arising from the disproportion between the limited 

 number of places in nature's household, and the excessive 

 number of organic germs. The origin of new species is 

 moreover greatly favoured by the active or passive migra- 

 tions of animals and plants, which takes place everywhere 

 and at all times, without being, however, entitled to rank 

 as necessary agents in the process of natural selection. 



The origin of new species by natural selection, or, what 

 is the same thing, by the interaction of Inheritance and 

 Adaptation in the struggle for life, is therefore a mathe- 

 matical necessity of nature which needs no further proof 

 Whoever, in spite of the present state of our knowledge, 

 still seeks for proofs for the Theory of Selection, only 

 shows that he either does not thoroughly understand the 



