The Origin of Organic Forms. 201 



is equally at fault. Mr. Spencer's own doctrine is 

 fairly open to the condemnation pronounced by him 

 on the view of Professor Owen : it is " a shaping of 

 ignorance into the semblance of knowledge .... 

 the fusion of separate unknown processes into a con- 

 tinuous unknown process." 



But if the dynamic hypothesis hold good, it affords 

 the basis for a theory of the origin of species markedly 

 different from that of natural selection. In account- 

 ing for the variety of organisms, the Darwinian theory 

 proceeds on the supposition that sameness of struc- 

 ture proves identity of origin. The various groups 

 of vertebrates, for example, are assumed to be differ- 

 entiated descendants from the same stock ; just as all 

 the varieties of pigeons have sprung from one pair. 

 It is taken for granted that sameness of structure 

 implies community of parentage. If the kangaroo 

 and the fox are alike in having a vertebral column, it 

 is concluded they must have had a common ancestor. 

 But the principle is not self-evident : on Mr. Spencer's 

 theory, it is not even probable. The advocate of 

 community of descent is liable to be charged, as Mr. 

 Spencer charges the creationist, with an imperfect 

 appreciation of the great principle of causation. For 

 the vertebrate structure is an effect; and similarity 

 of effects is due to similarity of causes. In so far as 

 the causes operating on living matter are the same, 

 the effects will be the same. If, as Mr. Spencer holds, 

 variation of incident fofces determines variety in the 



