EVOLUTION TODAY 441 



the past. In recognition of the universal importance of the associa- 

 tion of heritage and environment in all aspects of life we approach 

 the basis for sound future investigation. 



Science cannot be wholly satisfied until its ideas have been 

 demonstrated in the laboratory. If evolution is to reach this 

 happy state of proof, it will obviously not be due to the methods 

 of the past. At present the possil)ility of finding methods of 

 experimental proof seems remote, for with the facts described in 

 this chapter in mind it is evident that certain conditions must be 

 met. 



It would be foolish to expect, as has been done in the past, that 

 the induced change might persist after the removal of the stimulus 

 at the end of a few generations. Even though the heritable power 

 of the organism to respond to a given condition might have 

 changed this could not be expected, for the development of the 

 new response would not necessarily destroy the organism's capac- 

 ity for the old. Both old and new responses may be looked upon 

 as the positive results of different factors. 



If, however, a change can l)e induced and intensified by gradual 

 modification of the stimulus through many generations until a 

 result of considerable importance in individual life is attained, we 

 shall have an "acquired character" worth}^ of a test. And if the 

 character in question should develop accessory relationships of 

 value within the organism it will l)e even better. Under these 

 conditions we may expect the removal of the stimulus, if the 

 organism can still live under the old conditions, to be accomphshed 

 without the loss of the character. Even under such conditions we 

 would have to recognize that the change proceeded not from the 

 heritage nor from the environment alone, l:)ut from the two acting 

 together. And if such an experiment should fail, we must then 

 look for some unknown property in living matter which makes 

 its heritage in some degree independent of environmental condi- 

 tions. 



It is highly probable in the light of modern knowledge that the 

 explanation of evolution will be based upon the recognized facts 

 of biology. Living things as we see them now are exceedingly 

 varied and complex, l)ut if we could look back over the complete 

 record of th(Mr development we should probably find a tale of 

 gradually increasing complexity as each successive stage realized 

 the possibilities of its heritage and thereby made possible still 



