Variation and Heredity 275 



He then makes the following significant statement : " All 

 the characters above enumerated which are transmitted in 

 a perfect state to some of the offspring and not to others — 

 such as distinct colors, nakedness of skin, smoothness of 

 leaves, absence of horns or tail, additional toes, pelorism, 

 dwarfed structure, etc., have all been known to appear sud- 

 denly in individual animals or plants. From this fact, and 

 from the several slight, aggregated differences which dis- 

 tinguish domestic races and species from each other, not 

 being liable to this peculiar form of transmission, we may 

 conclude that it is in some way connected with the sudden 

 appearance of the characters in question." 



Darwin has, incidentally, raised here a question of the most 

 far-reaching import. If it should prove true, as he believes, 

 that inheritance of this kind of discontinuous variation is also 

 discontinuous, and that we do not get the same result when 

 distinct species are intercrossed, or even when well-marked 

 domestic races are interbred, then he has, indeed, placed a 

 great obstacle in the path of those who have tried to show 

 that new species have arisen through discontinuous variation 

 of this sort. 



If wild species, when crossed, give almost invariably inter- 

 mediate forms, then it may appear that we are going against 

 the only evidence that we can hope to obtain if we claim 

 that discontinuous variation, of the kind that sports are made 

 of, has supplied the material for evolution. If, furthermore, 

 when distinct races of domesticated animals are crossed, we 

 do not get discontinuous inheritance, it might, perhaps, with 

 justness be claimed that this instance is paralleled by what 

 takes place when wild species are crossed. And if domesti- 

 cated forms have been largely the result of the selection of 

 fluctuating variations, as Darwin believes, then a strong case 

 is apparently made out in favor of Darwin's view that con- 

 tinuous variation has given the material for the process of 

 evolution in nature. Whether selection or some other factor 



