INTENSIVE SE&EE&ATION. 315 



to use it as including both assuetude, wbicli is being accustomed 

 to, being practised in, habitual use, — and desuetude, which is 

 disuse, discontinuance of practice. This principle has been re- 

 cognized by most biologists, though it has recently been called in 

 question by Weismann. 



4. Emotional Transformation. — Dr. C. V. Eiley, of the National 

 Museum, Washington, has called attention to the influence of 

 parental emotions, especially maternal emotions during the term 

 of pregnancy, as a factor in evolution (Address " On the Causes 

 of Variation," before the Section of Biology, American Asso- 

 ciation, August 1888 ; also in ' Popular Science Monthly,' vol. 

 xxxiv. pp. 811-816). 



5. The cumulative development of adaptations through " the 

 survival of the fittest " when the fittest are other than average 

 forms. This is the principle of Unbalanced Selection or of 8e- 

 lectional Transformation. 



6. Transformation produced by the indiscriminate destruction 

 of a portion of a species, with the accompanying probability that 

 the remaining portion will not possess all the characters possessed 

 by the species previous to the elimination. Tliis principle I call 

 TTnbalanced Elimination, or JEliminational Transformation. 



7. Transformation produced by different degrees of amalga- 

 mation of the varieties and races which have resulted from previous 

 Segregations. In most species there is a constant process of 

 amalgamation by which thousands of minor varieties are absorbed; 

 but wdien the process proceeds beyond ordinary limits, and the 

 barriers that have divided well-marked races give way, transfor- 

 mation must follow. This principle I call Diversity of Amalga- 

 mation, or Amalgamational Transformation. 



8. The cumulative development of the more fertile of the forms 

 that are equally adapted. In other words, transformation pro- 

 duced by diversity in the relative fertility of varieties that 

 are equally adapted to the environment and the constitution of 

 the species, or by change in the degrees of fertility possessed 

 by the same variety at different times and in diflerent places. 

 This principle I call Unbalanced Fecundity, or Fecundal Trans- 

 formation. 



Of these principles, all, except the 6th, 7th, and 8th, have been 

 more or less discussed by writers on biology, though some of the 

 forms of Selection depending on the relations in which the 

 members of a species stand to each other have never been 



