56 HEREDITY AND SELECTION IN SOCIOLOGY 



adaptation. The fact is that at any point natural selection 

 may limit the further progression of a plus variation. To minus 

 variations, in the case of organs or characteristics harmful to 

 the species, there is no limitation other than of the complete 

 disappearance of the organ in question. But plus variations 

 are arrested as soon as they attain their object — that of adapting 

 the organism to its environment. Excessive variation is not a 

 cause of the extinction of the species, but results only in the 

 suppression of individuals who may exhibit it. 



Personal selection is a very important — perhaps the most im- 

 portant — factor in maintainiiag the constancy of a species. 

 Every excessive variation which breaks the harmony of the 

 species is at once eliminated by personal selection. The role 

 of germinal selection is a less important one. Theoretically, 

 there is no reason for supposing that the germ-plasm may not 

 have itself the power of checking the plus variations of any sort 

 which may arise within it. Support is lent to this theory by 

 the fact that numerous morphological variations which are 

 below selective value disappear after a while. And the fact 

 that many species are undoubtedly constant throughout very 

 long periods shows that not every movement among the deter- 

 minants towards a plus variation continues sufficiently far to 

 attain biological value. 



But the very fact that only those variations which are of purely 

 morphological value are capable of being controlled by germinal 

 selection demonstrates that the chief factor in regulating the 

 constancy of species is personal selection. Weismann has dis- 

 tinctly admitted that as soon as any plus variation has gone 

 beyond a certain point germinal selection alone is powerless to 

 hinder its further progress. In the case of ancient and conse- 

 quently constant species, the germ-plasm is fixed, the distinc- 

 tive determinants of the species stand little or no risk of being 

 weakened or eliminated, and variations which may arise are 

 immediately checked before they attain biological value— that 



