194 THE EVOLUTION THEOKY 



certain external influences : I refer to egg-cells which develop 

 parthenogenetically. 



If amphimixis is not a universal preliminary condition of repro- 

 duction, wherein lies the necessity for its general occurrence among 

 living organisms ? 



We have already learned that tliere are two results produced 

 without exception by amphimixis ; one of these is the antecedent 

 reduction of the original number of ids by one half, and the conse- 

 quent new combination of ids which results from this ; the other 

 is the union of two such halved germ-plasms from two different 

 individuals. The first we may, witli Hartog, compare to the removal 

 of half of a pack of cards previously mixed, the second to the com- 

 bination of two such halves from different packs. The first process 

 brings nothing new into the complex of primary constituents, but 

 rather removes a part — larger or smaller — of its characters : not 

 necessarily exactly half of these, since each individual kind of id may 

 be represented by doubles or multiples. But the reduction simj^lifies 

 the composition of the germ-plasm, and might by itself, through the 

 struggle of the ids in ontogeny, lead to a resultant different from 

 the parent, that is, to a new individuality. Through the second 

 process, however, new individual traits are of necessity added, and 

 make the resultants still more markedly diverse, that is, if the ids 

 of both parents attain to expression in the struggle of ontogeny, and 

 this, as we have already seen, is usually the case, though not always 

 and certainly not always in all parts. Thus amphimixis, together 

 with the preparatory^ reduction of the ids, secures the constant 

 recurrence of individual peculiarities through the ceaseless new 

 combinations of individual characters already existing in the 

 species. 



When sixteen years ago I hrst inquired into the actual and 

 ultimate significance of sexual reproduction, I thought I had found 

 it in this ceaseless production of new individualities. This seemed 

 to me a sufficient reason for the introduction of amphimixis into 

 nature, since the difference between individuals is the basis of the 

 process of selection, and thus the basis of all the transformations 

 of organisms, which we may refer to natural or sexual selection. 

 Now these differences of selection-value are- — as I believed then, and 

 do still — not only by far the most frequent organic changes, but also 

 the most important, since they not only initiate, but control new lines 

 of evolution. Therefore I still regard amphimixis as the means 

 by which a continual new combination of variations is effected 

 a process without which the evolution of this world of organisms 



