VIII CROSSING AND SELECTION 383 



organisms has grown in course of time out of cells. I 

 described the individual development as an abbreviation of 

 phylogenetic growth. 



Growth, in the sense of continual modification under the 

 influence of stimuli is a fundamental property of protoplasm. 



Since the manifold variety of the forms of the organic 

 ^vorld is due to growth, it is seen to be a necessary consequence 

 of that fundamental property. 



As I have already insisted in a previous passage,^ repro- 

 duction also is a fundamental property of protoplasm, because 

 it is indeed nothing else than continued growth ; and, I have 

 to add, since it essentially consists in the transmission of the 

 properties of one protoplasmic unit (person) to another, it is 

 on this fundamental property of protoplasm that the im- 

 mortality of life depends. 



Crossing and Selection as Indirect Causes of Growth 



Besides growth as the result of the action of stimuli, w^e 

 have to consider in relation to the production of the hetero- 

 o'eneity of the organic world, and as indirect causes thereof, 

 crossing (sexual mixture) and selection. Of these two cross- 

 ing alone is capable of creating anything new, of contributing 

 by its own action to the growth of the organic w^orld. This 

 possibility is due to the fact that by the mingling of two 

 forms a third new form may be produced. But this does not 

 occur to so great a degree nor so commonly as is frequently 

 assumed. ^Nevertheless the influence of crossing in the 

 modification of forms is an important one. Natural selection 

 can, as I have repeatedly remarked, create nothing new. It 

 only so far contributes to the growth of the organic world that 

 it selects the forms which are most fitted for life, and pre- 

 serves them for the future action of new stimuli and of 



1 p. 24. 



