340 DARWINISM AND THE PROBLEMS OF LIFE 



We might put a long list of questions to germinal 

 selection. Whence comes the greater amount of 

 nourishment that overcomes the self-regulation of the 

 determinants, and thus represents the real source of the 

 variations ? To what extent can a determinant grow 

 without injuring its neighbours ? How is it that 

 irregularities of the food-supply within a determinant 

 do not often lead to a complete transformation of it, 

 instead of merely altering its quality a little? 



But we have seen that we must reject the theory of 

 germinal selection, and may quit the subject. In the 

 next chapter we will return to it for a moment, in 

 order to disprove it once more from a different point 

 of view. 



Let us now look about us for other principles to 

 explain how organs reach a certain height owing to 

 constant definitely directed variations, so that at some 

 stage they acquire selective value and may be further 

 advanced by selection. 



There are experts who say that external influences 

 may not only affect an organism in the course of the 

 individual life, but that these modifications are trans- 

 mitted in a weaker form to its offspring, and are 

 accentuated in these, since they remain exposed to the 

 same influences. Thus in the course of generations the 

 external agency, which always remains the same, will 

 modify the animal more and more in a definite direction. 

 This steady variation in one direction owing to external 

 influences is called orthogenesis. 



Orthogenesis is, clearly, a subdivision of the 



