112 HEREDITY AND SELECTION IN SOCIOLOGY 



sanguinity does not necessarily involve degeneracy, for tlie 

 latter presupposes unfavourable variations as its antecedent 

 condition. As long as such unfavourable variations do not set 

 in, no degeneration can result from consanguinity. This is con- 

 firmed by the fact that the harmful results of consanguinity 

 are shown by experience to vary greatly in intensity, and may 

 even be completely absent."^ The most remarkable cases of 

 degeneracy caused by consanguinity are those produced by the 

 artificial breeding of wild races, which are not only subjected 

 to continuous unnatural endogamy, but which are also pro- 

 tected against the consequences of the artificial conditions under 

 which they live. 



Instances of a race surviving long periods of consanguinity are 

 not very frequent, and it is difficult to get secure data as to the 

 length of time during which these generations have prevailed. 

 On the other hand, there are not a few parthenogenetic species. 

 It is likewise impossible to ascertain how long such species have 

 remained exclusively parthenogenetic, but it is easier to under- 

 stand the persistence of a parthenogenetic species than of a 

 consanguineous one. The id complex of a parthenogenetic 

 species retains all the ids derived from the common ancestor. 

 The number of these ids does not diminish in quantity, for the 

 second maturation division does not occur in the case of partheno- 

 genetic eggs, and it will be remembered that the second matura- 

 tion division is the one which effects the reduction of the chromo- 

 somes to one-half their normal number. And, on the other 

 hand, if parthenogenesis does not allow of the renewal of the 

 germ-plasm, neither does it allow of the importation of con- 

 stitutional defects, as consanguinity does. If certain members 

 of a parthenogenetic species show a tendency to vary in an un- 

 favourable direction, such individuals are eliminated without 

 having had a chance of disseminating the determinants of these 

 unfavourable variations. Thus, a parthenogenetic species from 

 1 Vortrdge ilher Deszendenztheorie, ii. 195. 



