j6 bionomic laws. 



sh( >uld be i ibserved that it is not every kind of selection that produces 

 transformation. It is only as selection results in the preservation of 

 other than average forms that it has any influence in transforming a 

 race. The selection of average forms for propagation tends to pro- 

 duce stability of tvpe; and the selection of extreme, but of opposite, 

 and, therefore, balanced deviation from the type produces fluctuating 

 variation; but unbalanced selection, that is, propagation from forms 

 whose average character differs from the average character of the 

 race, changes in some degree the average character of the race in the 

 next generation. Whenever this takes place, whether it be by the 

 design of man or not, there transformation takes place. 



Unbalanced artificial selection is not the only principle producing 

 the unbalanced propagation of the variations of domestic races. Un- 

 balanced natural selection caused by change in climate or in other 

 external conditions, and resulting in the superior success of other 

 than average forms, will also produce unbalanced propagation of 

 domestic as well as of wild races. Again, it may be that some form 

 of variation that is above the average in strength or skill, or in the 

 length of natural weapons, or in the beauty of its adornments, will 

 gain an advantage over its fellows in the appropriation of food or 

 in winning mates, and so become subject to some form of reflexive 

 selection, by which unbalanced propagation is produced. 



There may also arise unbalanced elimination, when, through some 

 overwhelming catastrophe, a large portion of the domestic stock is 

 destroyed, and the remaining individuals that propagate do not repre- 

 sent the average characteristics of the race. This may be called 

 indiscriminate elimination. Indiscriminate elimination arises when 

 war, famine, pestilence, or earthquake falling upon a tribe of men 

 results in the indiscriminate destruction of nearly all of their domestic 

 animals; and in many of these cases the surviving individuals from 

 which the stock is afterward propagated do not represent the average 

 character of the previous stock. 



Again, some variation of the stock may be endowed with a degree 

 of fecundity decidedly above the average fecundity of the rest of the 

 stock; and, if the form possessing this superior fecundity is as well 

 adapted as other forms to meet the desires of those who raise the 

 creatures, unbalanced propagation will take place, and the average 

 character of the stock will be changed. In my paper on Intensive 

 Segregation* I call this principle fecundal transformation. Karl 

 Pearson has discussed this principle under the title of "reproductive 



* See Appendix II. 



