TRANSFORMISM 231 



number of digits, but intermarriage with individuals 

 belonging to the other pure strain would immediately 

 lead again to the transmission of the contrasting 

 characters, or allelomorphs, although marriage with an 

 individual belonging to the same pure strain would 

 carry on the normal or abnormal unmixed character 

 into another generation. But if the possession of six 

 fingers conveyed an undoubted advantage, and if 

 natural selection did really act in civilised man as 

 regards the transmission of morphological characters, 

 then a stable variety (Homo sapiens hexadactylus , let 

 us say) might be produced by its agency. The muta- 

 tions which we consider in the investigation of the 

 inheritance of alternating characters are therefore just 

 as much the material for natural selections as the 

 mutations which occur among the ordinary variations 

 displayed by organisms in general : but since only one 

 or two characters appear to be subject to this mode of 

 transmission, the process would be so slow as to be 

 inadmissible as an exclusive cause of evolution. 



If we assume that de Vries' mutations are the 

 material on which selection works, this difficulty is 

 immediately removed, for we now have to deal with 

 groups of stable deviations : not one or two, but all 

 the characters of the organism appear to share in the 

 mutability. But another difficulty now arises. A 

 species of plant or animal may have got along very 

 well with its ordinary structural endowment, and then 

 a number of individuals begin to mutate. Some of the 

 deviations from the specific type may be of real advan- 

 tage, but others may not : we can, indeed, imagine an 

 in-co-ordination between the mutating parts or organs 

 which would be fatal to the animal ; on the other hand, 

 there might be complete co-ordination, with the result 

 that great advantage might be conferred upon the 



