MENDELISM 63 



union of two wliitc-bearing gametes, some Vilack, since 

 formed by the union of two black-bearing gametes, 

 and some grey like their grey parents, since formed 

 by the union of a black-bearing with a white-bearing 

 gamete. But the gametes of this new grey indivi- 

 dual will not be grey, but black or white, as before. 



The discovery that variation — e.g. the birth of a 

 black individual to grey parents — may really be a 

 form of heredity, proceeding according to definite 

 laws, and this statement of the working of the pro- 

 cess, constitute Mendel's law of seu^recration. 



Such variations as these may be called mutations, 

 in order to distini^uish their 'Teat extent. From 

 Mendel's law it follows that we can no longer accept 

 the old doctrine quoted by Darwin that Nature does 

 nothing by leaps — ^er saltuTU. We see that new 

 species may suddenly arise by the operation of the 

 laws of heredity quite apart from any slow accumu- 

 lation of variations under the influence of natural 

 selection. As Bateson says : " The dread test of 

 natural selection must be passed by every aspirant 

 to existence however brief": but that expresses the 

 totality of its power. Natural selection selects; it 

 does not originate or create. 



Space fails here for the discussion of the many 

 facts which " Mendelism " and the " mutation 

 theory " help to explain. What, for instance, could 

 be more puzzling than the " limitation of licrcdity 

 by sex" ; the transmission of hiemophilia and colour- 

 blindness, for instance, from bleeding or colour- 

 blind males, through normal females, to their male 

 but not their female descendants ? M or the truns- 



^ See Chapter XIII. " Heredity ami Disease." 



