192 PHYSIOLOGIC GENETICS 



differences among local populations which can provide material for interdemic selection 

 (by differential population growth and dispersion). 



The relation of random drift to selection among demes is precisely analogous 

 to that of random mutation to mass selection within demes, but whereas the latter 

 deals only with the momentary net effects of single gene differences, the former deals 

 with genetic systems as entities. As I have always emphasized, neither random drift 

 nor random mutation is of appreciable evolutionary significance except in conjunction 

 with its appropriate kind of selection. 



It is because of the necessary prevalence of types of genie interaction that lead to 

 multiple selective peaks in the genetic system that I have always considered interaction 

 to be as important in evolutionary theory as in physiologic genetics. 



