12 The Mechanism of Evolution in Leptinotaesa 



neo-lamarckians. 



The neo-Lamarckians, although boldly maintaining the truth of Lamarck's 

 fundamental proposition of the eifect of the conditions of the medium, seem to 

 have been most uncritical in the use of the cardinal principle of their master, 

 and at the present time there is no evidence that the neo-Lamarckians' hypoth- 

 esis is true, and it is necessary to suspend judgment as to whether their principle 

 of the transmission of variations from the soma to the germ ever occurs. 



The essential principle in Lamarck's work, however, that differences in the 

 medium, and especially those resulting from change in habitat, are effective 

 factors in evolution, certainly must receive most careful experimental investiga- 

 tion, and it matters little whether the effect of the conditions of the medium are 

 direct upon the germ or indirectly through the soma to the germ. The principle 

 is now shown to be true that changing conditions in the medium are efficient 

 factors in the evolution process. 



Although forced now to admit the truth of Lamarck's essential principle of 

 the effectiveness of factors in the medium, we do not commit ourselves in any 

 way to the hypothesis of the neo-Lamarckians, nor is it possible to do more than 

 recognize that if their principle is effective in evolution, further consideration 

 and use of it can only be the product of exact experimental investigation. 



The chief principle of Lamarck, however, iinds a permanent place in the 

 hypothesis of transmutation by means of natural selection as enunciated by 

 Darwin, which was a far broader conception of organic evolution, wherein he 

 made great use of the effect of environment so emphasized by Lamarck. Darwin 

 forcefully and frequently insists that the agencies most productive of the 

 differences in any population of organisms, which become the basis of the 

 selective process whereby species or changes are produced, are in considerable 

 part the direct product of the action of the conditions in the medium upon the 

 organism, and especially upon the reproductive process, and probably upon the 

 reproductive elements. 



DARWINISM. 



The hypothesis enunciated by Darwin has proven far from satisfactory when 

 applied generally in the attempt to solve the riddle of evolution in plants and 

 animals. Darwin recognized the Malthusian principle that every species tends 

 to increase at a rapid rate and to produce a gi'eater number of individuals than 

 are capable of survival, and that of these 98 per cent in the main die before 

 reaching maturity, only 2 per cent surviving to reproduce the next generation. 

 It is axiomatic that there is this excess of reproduction over survival, and the 

 whole of Darwin's hypothesis of transmutation hinges upon the single point of 

 whether those individuals which persisted and reached maturity are those which 

 possess variations of a nature such that they are thereby made more efficient 

 than their fellows, and hence better able to successfully compete in the " struggle 

 for existence," or whether the survivors are only those individuals whose chance 

 position, when the accidents of life happen, save them from extinction, and 

 eliminate their less fortunately placed companions. If it is true that the sur- 

 viving minority are the possessors of conditions making them more fit to meet 

 the struggle for existence, then Darwin's hypothesis has a considerable degree 

 of probability of truth, but it distinctly has not been shown that the surviving 



