16 THE PRINCIPLES OF HEREDITY 



Lamarckian hypothesis be true, then, even if it be only a 

 partial explanation of the facts, the evolution and degenera- 

 tion of many living races, especially of the higher animals, 

 must be proceeding on lines of enormous complexity. All 

 the immense variety of influences acting on them must be 

 producing slow changes in all the huge complex of their 

 multitudinous structures. Here also the Lamarckian 

 doctrine is in fundamental opposition to its rival. 



27. The Darwinian, or rather the Neo-Darwinian theory of 

 evolution by Natural Selection, does not possess the fascin- 

 ating simplicity and obviousness of the Lamarckian doctrine. 

 It is founded on two ascertained facts, and two inferences 

 which its supporters maintain are legitimate : (a) It insists 

 on the universal occurrence of variations as a law of nature. 

 But, except that it rejects the Lamarckian explanation of 

 variations, it does not at least as held by the majority of 

 its supporters necessarily concern itself with the question 

 of their causation. It is sufficient for its purpose that 

 variations do occur in every organ and structure of every 

 living being. (Z>) It asserts that the number of individuals 

 in any species which survive and beget a full quota of off- 

 spring is not the same as the number that come into being. 

 Immense numbers perish before reaching old age or even 

 maturity, (c) It infers that, as a rule, the individuals who 

 survive and have offspring, are those which are better fitted 

 to the environment in which they are placed than those 

 which perish, (d) Lastly it infers that by this survival of 

 the fittest and elimination of the unfittest the " specific 

 mean " the average of the race is raised in successive 

 generations, whereby evolution results. Nature in fact is 

 supposed by it to act on precisely the same plan as a breeder 

 who wishes to improve his stock of plants and animals. 1 

 She permits, on the whole, only a certain type of individuals 

 to have offspring those the best suited to their environments. 

 In the case of antelopes, for example, she has eliminated 

 with greater or lesser certainty all individuals incapable of 

 withstanding want, hardship, or disease, or who are deficient 



1 It is curious that during every age men have accepted as a belief 

 the method of evolution laid down by Lamarck, but have followed as a 

 practice that laid down by Darwin. In other words they have believed 

 that races change in the manner described by Lamarck, but have sought 

 to improve their own plants and animals in the manner described by 

 Darwin. The reader will note that Neo- Darwinians necessarily reject 

 Darwin's theory of Pangenesis, since that hypothesis assumes the 

 transmission of acquirements. 



