160 HEREDITY AND SELECTION IN SOCIOLOGY 



neotaxis of the germ-plasm were less productive of heterogeneous 

 id combinations, the number of heterogeneous individuals 

 composing a species would be reduced. And, for the purpose 

 of natural selection, it is not the number of homogeneous, but 

 the number of heterogeneous, individuals which counts. A 

 species which contains a million individuals, each of which is 

 homogeneous with all the rest, has merely the selective value 

 of one single individual. We thus see the immense importance 

 of the reducing divisions and of amphimixis in effecting varia- 

 tions. We are justified, indeed, in regarding these processes 

 as the ultimate source of all organic variation. 



Although the number of possible combinations resulting from 

 amphimixis between two individuals is very large, nevertheless, 

 when we remember that, in the case of the male partner especially, 

 an enormous number of germ-cells are produced ia a lifetime, it 

 will appear probable that several of the progeny of the same pair 

 of parents will be homogeneous. As heterogeneity is essential 

 for natural selection to act upon in order to efEect adaptation, it 

 is not surprising to find, if we may speak figuratively, that 

 Nature has taken further means to ensure the necessary amount of 

 heterogeneity. Recent observation has shown that, in some 

 cases, the male and female elements in the nucleus of the 

 fertilised ovum remain distinct from each other right through 

 the embryonic development until the germ-cells of the offspring 

 appear. It may be that this distinctness is maintained all 

 through the ontogeny. But if the male and female elements, 

 instead of being blended in the primitive germ-cell, remain 

 distinct from each other throughout the ontogeny, the total 

 number of combinations realisable by the union of male and 

 female chromosomes is not exhausted when amphimixis is 

 effected ; fresh combinations may present themselves at every 

 successive reducing division, in the production of all the countless 

 germ-cells during the life of the individual. 



The child is the resultant of the determining forces of all the 



