CHAPTER X 



CONCLUSIONS 



At the present time there are two rival conceptions of organic 

 evolution which represent a fundamental cleavage in scientific 

 outlook. The one views the living organism as the resultant 

 of variation (either spontaneous or induced by external factors) 

 guided by the fortuitous changes of its environment. The other 

 regards the organism as charged with a self-initiating capacity 

 for development and adaptation and the modifications dis- 

 played in the course of evolution as the expression of this 

 potential. The first, stressing the intimate relation of the 

 organism with its environment, its apparent ' fit ' in the ecolo- 

 gical complex, and the proof that evolution has proceeded by 

 minute increments, finds the prime cause either in Natural 

 Selection or in the direct moulding of the organism by the 

 factors of the environment. The other emphasises the co- 

 ordination and mutual interaction of the parts of the organism, 

 its wholeness and organisation, and, unable to imagine that 

 such organisation can be produced by the mechanical sieving of 

 variants by selection or by the erratic stress of the environment, 

 assigns the origin of evolutionary modifications to an internal 

 energy. It is readily understood how this diversity of opinion 

 has arisen, for the present incoherent and unrelated state of 

 the data makes it easy to seize on certain kinds of evidence and 

 treat them as decisive. We have stressed in a previous chapter 

 the part played by prejudice and bias in evolutionary inquiry. 

 It is not sufficiently realised, however, how limited and 

 inadequate are our data for coming to a decision as to the 

 causes of evolution. Any attempt, therefore, to form an 

 unprejudiced conclusion labours under technical disadvantages 

 which frustrate it and limit it to a summing of possibilities. 

 We propose in this chapter to define as clearly as possible 

 the limits of our knowledge on these matters, and in particular 



