426 ANNUAL, REPORT SMITHSONIAN INSTITUTION, 1918. 



do not exclude its action from their schemes of evolution. They only 

 object to the exaggerated part attributed to it by those whose concep- 

 tions of descent are influenced by their sociological or supernatural 

 consideration, and they understand that natural selection surely gives 

 stability to the effects of the direct action of environment. Most of 

 them also recognize that by the side of these two main factors of 

 evolution one must take into consideration the two aspects — indi- 

 vidual and social — of the struggle for life, the development of pro- 

 tective instincts in the higher animals, and the effects of use and dis- 

 use of organs, crossing, and the occasional appearance of more or less 

 sudden variations — all these having their part in the evolution of the 

 unfathomable variety of organic forms. 



Among the modern biologists, Prof. Plate has perhaps best un- 

 derstood the necessity of a synthetic view of the factors of evolution, 

 which he has developed in his elaborate work, now known under 

 the title of " Selektionsprinzip." He examined first in detail the 

 scope and the possibilities of natural selection under the different 

 forms of the struggle for life, and after having shown that natural 

 selection steps in where the Lamarckian direct adaptation fails, and 

 that single-handed it would not be sufficient to solve the problem of 

 the origin of species, Prof. Plate sums up his opinions in the fol- 

 lowing lines which, in the present writer's opinion, are a fair state- 

 ment of the case : 



The only real difficulty for Darwinism is [he writes] that the variations must 

 attain a certain amplitude before they are "selection-worth"; that is, before 

 they give to selection the opportunity to step in. Minimal individual differ- 

 ences can call forth no selection. However, I have shown already at some 

 length (pp. 109-179) that after a careful study of the problem this difficulty 

 proves to be illusory, because, on the one hand, it is impossible to deny that 

 there are variations worthy of being selected, 1 and, on the other hand, there are 

 in nature different ways for increasing the minimal differences, so that they 

 do become worthy of selection. Of these different ways, the modification of 

 functions, the changes in the conditions of life, use and disuse, and orthogenesis 

 enter into the category of the factors indicated by Lamarck, and therefore the 

 selection theory can not refuse the collaboration of the Lamarckian factors. 

 Darwinism and Lamarckism, 2 taken together, give a satisfactory explanation of 

 the growing up of species, including the origin of adaptations, while neither of 

 these two theories, taken separately, gives it. ( Selektionsprinzip, pp. 602-603. ) 



Let me only add, to avoid misunderstandings, that the Lamarckism 

 of which I have spoken in these pages and which Plate has in view in 

 the just given quotation means the teachings of Lamarck as they 

 appeared in his Philosophie zoologique, his remarkable Discours 

 d'ouverture de Fan X et de l'an XI, delivered at the Academy of 



lOne must, however, ask whether such sudden variations appear in sufficient num- 

 bers. — P. K. 



2 "I mean, of course [he added in a footnote!, only the causal-niedianical part of 

 Lamarckism, not its autogenetical and psychical ideas." See pp. 501, 504. 



