34 8 Evolution 



This way of looking at the origin of variation has 

 had the effect of putting an end to the vague specula- 

 tions concerning the evolution of one form from another. 

 We demand today the experimental test when such a 

 statement is made and as a consequence the amount 

 of mere speculation in this field has diminished 

 considerably. 



It is possible that any further progress concerning 

 evolution must come by experimental attempts to 

 bring about at will definite mutations. Such attempts 

 have been reported but they are not all beyond the 

 possibility of error. 1 The most remarkable among 

 them are those by Tower who by a very complicated 

 combination of effects of temperature and moisture 

 claims to have produced definite mutations in the 

 potato beetle. The conditions for these experiments 

 are so expensive and complicated that a repetition by 

 other investigators has not yet been possible. 



It is, however, still uncertain whether the mere addi- 

 tion or loss of Mendelian characters can lead to the 

 origin of new species. Species specificity is determined 

 by specific proteins (Chapter III.), while some Mende- 

 lian characters at least seem to be determined by hor- 

 mones or substances which need neither be proteins nor 

 specific for the species. 



1 For a critical discussion of the details, see Bateson, W., Problems 

 of Genetics, New Haven, 1913, Chapter X. 



