CHAPTER VI. 



THE PROBLEM OF THE ORIGIN OF SPECIES— DISCUSSION, SUMMARY, AND 



CONCLUSION. 



In the preceding chapters facts from observation and experiment have 

 been brought together and correlated within narrow fields, and these in turn 

 within broader fields, in the attempt to arrive at the more general axioms 

 concerning animal evolution as it is revealed through the study of Leptino- 

 tarsa. This investigation began with the most general facts concerning these 

 beetles, their systematic position, distribution, and ecology, and from these 

 passed to more important and critical phases of their history. In this chap- 

 ter we shall attempt to bring together and correlate the accumulation of facts 

 and minor conclusions in the preceding chapters, that we may derive, if pos- 

 sible, more general axioms concerning the phenomena of evolution as discov- 

 ered in these beetles. 



The slow evolution of the idea of evolution, from its crude beginnings to 

 its wonderful development within the past century, has not solved the riddle, 

 but only crystallized out the separate fundamental problems, which, although 

 interdependent, can for the present be best investigated as separate problems, 

 and the results combined into more general laws. The fundamental prob- 

 lems of animal evolution are those of — 



(i) Heredity, the most important and most difficult of solution. 



(2) Variation, next to heredity the most widespread of organic phenomena. 



(3) Method of evolution — that is, in what manner or by what methods 

 have species, genera, and larger systematic groups been brought into exist- 

 ence? 



(4) Adaptation, or the adjustment of the animal to some one set of condi- 

 tions of existence. 



In this paper we are largely concerned with the method of evolution — that 

 is, whether species come through variation and heredity by one or the other, or 

 all of the methods proposed during the last hundred years. In this chapter, 

 therefore, I shall consider the accumulated facts as they bear upon the prob- 

 lem of the method of the origin of species. The great factor, heredity, we 

 must accept as acting, as we know it does, without attempting to examine 

 into it at all. If we accept heredity as a process acting in nature, we shall 

 in no way invalidate any arguments or conclusions that we may enter into 

 concerning the origin of species. In thus broadly accepting heredity as at 

 work in evolution, I also include within this same acceptance that of the 



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