THE THEORY OF ORGANIC EVOLUTION. 44! 



arise ? In what proportion are they continuous or 

 discontinuous, definite or indefinite? How far is 

 natural elimination discriminate ? To what extent 

 is isolation demonstrable ? before these and a score 

 of similar questions we stand not less expectant but 

 perhaps less confident than the evolutionists of a 

 third of a century ago. It is not that we are where 

 we were thirty years since ; it is rather that we have 

 become more aware of our ignorance and of the com- 

 plexity of the problem. 



It is a critical mood that becomes us as a reaction 

 from earlier enthusiasm, and the value of this is 

 borne out by the history of science which shows that 

 the rate of intellectual progress may be measured by 

 the periodicity of the wave of scientific scepticism. 

 But it is not a hands-in-the-pockets scepticism that 

 becomes us as evolutionists, it is a thdtige Slcepsis, 

 eager to test and measure, to experiment and observe. 

 After half a century of measurement and experi- 

 ment, the voice of the evolutionist will probably re- 

 gain confidence. What is especially needed is a 

 national or inter-national institute of experimental 

 evolution where the trials and testings could be con- 

 tinued for generations by a carefully recruited staff, 

 and thus remain unaffected by the death of individ- 

 ual workers. 



