CHAPTER VII 



CONSANGUINITY 



We have seen that the biological value of amphimixis lies in the 

 continuous renewal of the germ-plasm of the difierent individuals 

 of a species. This renewal secures the timely suppression of a 

 number of variations which would otherwise prejudicially afiect 

 the stability of the species. Moreover, by disseminating those 

 determinants whose variation tends to secure an ever greater 

 equilibrium, amphimixis contributes likewise to stability by 

 rendering readaptation possible, and by consolidating adapta- 

 tion already partially secured. We were led to reject the theory 

 of amphimixis as a " rejuvenating " factor ; and we must also 

 dismiss the theory which attributes to amphimixis a mysterious 

 " formative power," since there are cases in which a species con- 

 tinues exclusively by parthenogenesis. If amphimixis involved 

 a formative power, it is difficult to see how such parthenogenetic 

 species could survive. 



If the constant renewal of the germ by the continuous mingUng 

 of heterogeneous germ-plasms be advantageous to the species, it 

 might be inferred that consanguinity is biologically harmful to 

 the species in which it occurs. This, however, is not necessarily 

 the case, as we shall see. In the meantime, we may be better 

 able to understand how consanguinity might have a prejudicial 

 influence if we compare the result of amphimixis in the case of 

 exogamous pairing with that in the case of endogamous pairing. 



The result of amphimixis in exogamous pairing, is to import 

 into the germ-plasm of the product ids of heterogeneous type — 



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