102 ON HEREDITY. [IT. 



knows are unconscious, for they are beyond my province. In 

 this matter, there can be no suggestion of adaptation depending 

 upon a struggle between the various parts of the organism 

 (Roux)^ Natural selection cannot operate upon the different 

 epithelial cells which secrete the egg-shell o{ Apiis, since it is 

 of no consequence to the animal which secretes the egg-shell 

 whether a good or a bad shell is produced. Natural selection 

 tirst operates among the offspring, and the €gg with a shell 

 incapable of resisting cold or drought is destroyed. The dif- 

 ferent cells of the same individual are not selected, but the 

 different individuals themselves. 



In all such cases we have no explanation except the opera- 

 tion of natural selection, and if we cannot accept this, we may 

 as well abandon any attempt at a natural explanation. But, in 

 my opinion, there is no reason why natural selection should be 

 considered inadequate to the task. It is true that the objection 

 has been lately urged, that it is inconceivable that all the won- 

 derful adaptations of the organism to its surroundings can have 

 arisen through the selection of individuals ; and that for this 

 purpose an infinite number of individuals and infinite time 

 would be required ; and stress is laid upon the fact that the 

 wished-for useful changes can only arise singly and very rarely 

 among a great number of individuals. 



This last objection to the modern conception of natural selec- 

 tion has apparently some weight, for, as a matter of fact, useful 

 variations of a conspicuous kind seldom appear, and are often 

 entirely absent for many generations. If we expect to find 

 that qualitative changes take place by sudden leaps, we can 

 never escape this difficulty. But, I think, we must not look 

 for conspicuous variations— such as occur among domesticated 

 animals and plants — in the process of the evolution of species 

 as it goes on in nature. Natural selection does not deal with 

 qualitative but quantitative changes in the individual, and the 

 latter are always present. 



A simple example will make this clearer. Let us suppose 

 that it was advantageous to some species— for instance the an- 

 cestors of the giraffe— to lengthen some part of the body, such 

 as the neck : this result could be obtained in a relatively short 



* Wilhclm Roux, ' Der Kampf der Theilc im Organismus.' Leipzig, 

 i88i. 



