PSOBLEMS AND CONCEPTS OP EVOLUTION 11 



present time, been mainly concerned with the methods of transmutation of the 

 units of natural species. The principal problem of the student of evolution has 

 been to discover the causes of the production of species, and then to be able to 

 experimentally produce them. This investigation in the past century has 

 given several hypotheses of the mechanism of transmutation. 



HYPOTHESES OF SPECIES TRANSMUTATION. 



None of the several theories propounded appears to give a satisfactory explana- 

 tion of the problems of origin of species. The formation of species by the 

 Darwin-Wallace factors has many difficulties to overcome, and its later modifi- 

 cations, wherein transmutation was the result of the accumulation of minute 

 fluctuating variations conditioned by the play of mystic entities in the germ- 

 plasm, involves a degree of credulity not common among scientific workers out- 

 side of biologists of the neo-Darwinian school. Others have tried to reestablish 

 the principles of Lamarck that the stress of the conditions under which the 

 animals live induces modifications that are transmitted to subsequent genera- 

 tions. Still others, through inability to substantiate the fundamental idea of 

 the Larmackian theory, and unable to make progress with neo-Darwiaism as a 

 working hypothesis, have conceived of evolution as due to a jumping process, 

 and sought for data to prove that new characters or modifications of old ones 

 arose directly through sports, and that these become the progenitors of race and 

 species. 



Not satisfied with any of the preceding hypotheses, the attempt has been made 

 to find an efficient cause for the origin of species in geographical and physio- 

 logical isolation, but especially that geographical isolation which comes from 

 the segregation of the different portions of the same organized form in tmlike 

 habitats, and hence in different environmental surroundings ; while in another 

 line of effort, orthogenesis, one finds, in the writings of the authors supporting 

 the hypotheses, evidences of the old Aristotelian concept of an impelling 

 principle or of a goal with a fixed line of development in the evolution of 

 organisms. With this array of hypotheses it is no wonder that the layman is 

 confused and inclined to think that perhaps after all evolution may not be as 

 universal a truth as some of its advocates have claimed it to be, and even the 

 biologist often wonders what the outcome of this situation will be. 



The oldest of these hypotheses of species formation — that of Lamarck — ^was 

 formulated when many things now common knowledge were unknown. Lamarck 

 in his time knew something of the direct effect of external conditions in inducing 

 changes in organisms, especially in plants when they were transplanted into the 

 botanical gardens of Europe from exotic locations, and these direct effects of 

 the transplantation were noted, and this seems to have furnished Lamarck with 

 a possible natural cause of the formation of species. Lamarck recognized that 

 unless this modification was transmitted to subsequent generations no evolution 

 could result — which was certainly correct — and hence the idea of the trans- 

 mission of these through the reproductive process. It is true that Lamarck was 

 never clear as to how these characters were transmitted nor how they could be 

 transmitted, excepting that transmission from generation to generation was in 

 some way associated with the reproductive process and was necessary for the 

 transmutetion of species in evolution. 



