2 The Mechanism of Evolution in Leptinotaesa 



a narrow contact zone of great stresses from all other natural productions of 

 the planet. This living substance, which we as part thereof seek so diligently to 

 understand, and the question of whose origin has been a dominating factor in 

 human intellectual activities through all time, presents to all — scientist, theo- 

 logian, or layman — questions of fundamental interest. 



As human understanding of this living substance becomes clearer, and as 

 investigation becomes more accurate and analytical, there is increasing proof of 

 the sole operation of purely physical principles in the production of the char- 

 acters and reactions of this living stuff, and some of us, therefore, hopefully 

 look forward to that time in the future when all organic phenomena are capable 

 of statement in purely physical terms. Only some few more or less superficial 

 processes are capable of formulation in physical terms, while a wide array of 

 organic activities, of form and species, and in man the intellectual capacities — 

 memory, thought, and study of himself and nature — are hardly capable of 

 accurate formulation upon any naturalistic physical basis; that is, more than 

 the description of our reactions in terms of the general reactions of living 

 materials. 



Certain properties common to all of this living substance, the evidence of 

 the remains of this substance upon the planet, with increasing complications 

 of the primitive attributes and qualities common to all, have forced upon us 

 belief in some natural means of production of this diversity and increasing 

 complexity, with the present array of living types, of which man appears to us 

 as the most complex. 



It is profitless to debate whether there is in living things any agency or 

 principle above and apart from the rest of the physical imiverse, whether there 

 be a vitalistic content, entelechy, or soul; any and all of these terms are but 

 designations of a collective unknown, unanalyzed series of phenomena, whose 

 aid is invoked in a causative sense in the effort to present a mentally complete 

 picture of natural causation. The use of the unknown and unanalyzed, as a 

 cause, in the efforts of modern vitalists is not only unwarranted, but is distinctly 

 a retrogressive tendency, much of which is due to the influence of Kantian 

 philosophy. There is no denying the fact that the imknown with regard to the 

 phenomena of life exceeds the known, but at present that which is organized 

 knowledge is vastly increased over that of a century ago, and in this increase 

 understanding has at all times and in all directions been solely along the line 

 of the application of physical principles to the solution of the problems of living 

 substance, so that for the present we are justified in the belief that it is the only 

 safe point of departure in the effort to solve these riddles of living matter. 



Further justification for this attitude comes from the fact that not a single 

 advance has ever come from the vitalistic point of view, and while a vitalistic 

 conception or principle may help in certain metaphysical ramblings, or save 

 some frail intellect from despair at the incompleteness of knowledge as to the 

 causation of the phenomena of life, it serves no other end. At no time have any 

 conceptions of this kind given the least aid in investigation or in the attainment 

 of actual results in the solution of our problems. At all points the physical 

 conception of life and its evolution, at present fragmentary, is nevertheless the 

 only conception that has been of any service as a basis for the effort to under- 

 stand these phenomena, and finally to comprehend what our understanding of 

 these means in terms of cause and effect. 



