Introduction 479 



for him what is now known as the Hardy-Weinberg law, the basic 

 fact of population genetics. At the same time I analyzed the genetics 

 of industrial melanism in the nun moth ( Goldschmidt, 1921a; see 

 also 1948fo), in which a melanic mutant form had replaced a white 

 one in industrial areas within a known number of decades. After 

 analyzing the genetic differences between the two types (three pairs 

 of alleles, one sex-linked) I made a calculation of the mutation 

 pressure needed to replace one form by the other in the known time. 

 As the required mutation rate was too high to be possible, I concluded 

 that the dark form must have a selective advantage. This, then, was 

 a simple case of population genetics at the lowest level of micro- 

 evolution. 



At the same time it was realized that the first attack upon the 

 genetic solution of evolutionary problems should be made by ana- 

 lyzing what Darwin had called "incipient species," the subspecies, 

 which contemporary taxonomy had again pushed into the foreground 

 in the Rassenkreis concept of the species ( Kleinschmidt, Jordan, 

 Rensch ) , a fact which most geneticists realized only decades later ( the 

 "new" systematics ) . Sumner started the genetic and ecological analysis 

 of the subspecies of Peromyscus (final review, 1932), and I did the 

 same simultaneously for Lymantria dispar (final review, 1934c). Both 

 found that the subspecies differed from each other in definite Men- 

 delian combinations. It was further established that some if not all of 

 these genetic differences were of an adaptational nature, directly or 

 indirectly. In 1917 and up to the early 20's I had already come to the 

 conclusion — shared by Baur and East — that genetics leads back to 

 Darwin and that especially numerous small mutants, accumulated by 

 selection for the sake of adaptation, will account for speciation, 

 exactly as Darwin saw it. (One non-technical article of mine had the 

 title "Return to Darwin.") 



A new period of genetical analysis of evolution below the level of 

 the species — the only part accessible to genetic experimentation, not 

 counting a few exceptions — began when Fisher (1919) and Wright 

 (1921) worked out the statistical consequences of Mendelian breed- 

 ing within populations under all types of mating; while Haldane 

 ( 1924 ) added all the consequences for selection. Subsequently, Hal- 

 dane, Fisher, and Wright explored in detail what happens in inter- 

 breeding populations from the point of view of distribution, isolation, 

 selection or discarding of genie combinations, with and without selec- 

 tion. The general result was that shifts in genetic constitution and 

 isolation of new recombinants leading to adaptation to diverse environ- 



