Evolution of Evolution-Theory. 229 



(a) As we have seen, the great gap in Darwinism is 

 the absence of a theory of variation. It is assumed that 

 there has been a continual crop of variations usually 

 spoken of as fortuitous, indefinite, and small in amount 

 on which the sickle of natural selection has operated. 

 As to the causes of the crop nothing is said Darwin 

 simply confessing that the problem was beyond his 

 powers of solution. To Weismann, however, belongs 

 the credit of having taken several bold steps into the 

 darkness. For a time Weismann emphasizes the evolu- 

 tionary interest of the ancestral Protozoa, which, being 

 more liable to external influences than the higher crea- 

 tures are, were supposed to have accumulated a suf- 

 ficient stock of qualities or possibilities to account for 

 all the apparent new departures on the part of their 

 descendants. All variations among Metazoa, in short, 

 were regarded as combinations and permutations of 

 what the Protozoa had acquired. 



Then, for a while, Weismann emphasized amphimixis 

 that mingling of qualities which occurs in fertilization 

 at the origin of each new life; and again he added to 

 this another source of change prior to fertilization, 

 namely, in the reducing divisions which take place in 

 the maturation of the ovum, or in the course of sper- 

 matogenesis. 



Of late, however, Weismann has spoken more frankly 

 in regard to yet another source of variation, although 

 that involved in amphimixis and reducing-divisions is 

 still recognized. He speaks of the primary constituents 

 of the germ having a certain scope for variation among 

 themselves, and supposes a struggle of parts not only 

 in the body, as Roux did in his famous Kampf der 

 Theile im Organismus, but in the germ. There is an 

 intra-germinal struggle and selection. 



But much more than this. He says: "We are 

 undoubtedly justified m attributing the cause of varia- 

 tion to the influence of changed external surroundings". 

 This means that a change within an animate system 

 must be traceable in the long-run to a change in the 

 larger system of which the organism forms a part, and 

 that certain big environmental changes, e.g. of climate 



