4 HEREDITY AND SELECTION IN SOCIOLOGY 



that of a race of pigeons whose variation from the normal typa 

 has diverged to such an extent that the beak is too short and 

 delicate to be able to break open the egg, and the breeder has to 

 assist in the act of hatching.^ 



In addition to the individual fluctuating variations, there are 

 also sudden and far-reaching transformations which result, by 

 a sudden bound, in a new specific type. The Dutch naturalist 

 De Vries has especially insisted on these sudden transformations 

 to which he has given the name of mutations, and which he 

 distinguishes from the smaller and slower individual varia- 

 tions. According to De Vries, it is to mutation and not to 

 individual variation that the transformation of species has been 

 mauily due. 



The second factor of evolution, according to the Darwinian 

 doctrine, is that impUed in reproduction itself — the factor of 

 heredity. By heredity is to be understood the faculty possessed 

 by an organism for transmitting its qualities, physical and 

 psychical, to its offspring. All higher organisms possess a 

 peculiar substance localised in the nucleus of the reproductive 

 cell, which transmits the heritable qualities from parent to 

 offspring. Heredity is concerned with those characters which 

 are transmitted directly from the parents to the offspring, or 

 with those quaUties which offspring are capable of acquiring 

 independently of their parents, but which, nevertheless, so per- 

 meate the transmitting substance that the next generation can 

 inherit them directly. Thus many beheve that an individually 

 acquired predisposition to a disease may, as a predisposition, be 

 transmitted to the next generation. 



The third factor is that of excessive fecundity. " There is no 

 exception," wrote Darwin, " to the rule that every organic being 

 naturally increases at so high a rate that, if not destroyed, the 

 earth would soon be covered by the progeny of a single pair. 

 Even slow-breeding man has doubled in twenty-five years, and 

 ^ Darwin, The Origin of Species, p. 106 (edition 1902). 



