60 THE PROBLEM OF EVOLUTION 



The apparent repetition of many previous stages 

 of development is accounted for by the fact, that 

 it is essential to the very nature of evolution to 

 advance from what is simple to what is complex. 

 The more highly any animal is organised, the more 

 stages of development must it pass through, before 

 reaching the complex final stage, and it is quite in 

 accordance with nature that the previous transi- 

 tional stages, being simpler, should resemble the 

 final stages of other animals, which have remained 

 stationary at a lower degree of organisation. This 

 constitutes no proof that the human race has 

 passed through all these stages, but it only shows 

 that the evolution of the individual goes on from 

 the first subdivision of the impregnated ovum, 

 through various stages, until the final form of the 

 perfect organism is reached. 



I maintain therefore that we cannot accept the 

 biogenetic principle in its entirety, nor can we sanction 

 its application to man in order to prove his descent 

 from beasts. 



I shall be met, no doubt, with the objection that 

 there are stages in the development of the individual 

 human being, for which no explanation is possible, 

 unless we regard them as repetitions of an earlier 

 race-evolution. The most important of them in 

 this connection are the so-called branchial arches 

 and clefts of the human embryo. 



ciple ' altogether. On this subject cf. my Biology, chap. ii. pp. 457, etc. 

 See also the remarks on Dr. Schmidt-Jena's speech in Part n. of the 

 present work. 



