78 THE EVOLUTION THEORY 



germ are primary, and they determirLe the course of i^hylogenesis, 

 while the tissue-selection in the individual life only elaborates and 

 improves, according to the demands made upon it, the material 

 afforded by the primordial equipment of the germ. 



The American palaeontologist, Osborn, cites the case of the 

 horse's feet as an example in support of his view that modification 

 brought about by use in the individual life must be transmitted 

 in order that the phyletic transformations may be brought about, 

 but this example is perhaps the best that could be chosen to prove 

 the contrary. He supposes that, in every young horse, the means 

 of locomotion are improved at every step, so to speak, through the 

 contact with the ground, and I am quite willing to admit that 

 this is so. But that only proves that, even now, an elaboration 

 and improvement of the equipment which the germ affords is 

 indispensable, as it has been at all times and in all animals, and 

 thus that, notwithstanding the enormous number of generations 

 which our modern horse has behind it, the functional acquirements 

 of the individual have not yet been impressed upon the germ. Why 

 not? Because the horse becomes perfect without this, and there 

 was no reason why personal selection should perfect the primary 

 constituents of the germ still further, since the finishing touch 

 of perfection through use is readily afforded by the conditions of 

 each individual life. 



Moreover, when Osborn, Cope, and other palaeontologists empha- 

 size that, in phjdetic evolutionary series, definite paths of evolutionary 

 change are adhered to, and are not deviated from either to right 

 or to left, they are undoubtedly right, but the conclusion which 

 they draw is not justifiable, whether they assume with Nageli that 

 there is a power of development, a principle of perfecting, or whether, 

 as Osborn does, they assume the transmission of the modifications 

 brought about through use in the individual life. There remains 

 a third possibility, that the quiet and constant evolution in a definite 

 direction is guided by selection, and as, in passively useful parts, that 

 principle alone is admissible, I see no justification for assuming it 

 to be inoperative in regard to those which are actively functional. 

 All these variations which have led up, for instance, to the modern 

 form of the horse's foot are useful; if they were not, they could 

 not have been produced either by use or by disuse in the indi- 

 vidual life. 



At the same time, here again, we are justified in inquiring 

 whether the assumption of ' chance ' germinal variations, which we 

 have hitherto made with Darwin and Wallace, affords a sufficient 



