SPECIES AND VARIETIES. 197 



al selection, and there is no fundamental difference between 

 varieties and species. Varieties are incipinet species. He clearly 

 demonstrated, that there is no fmidamental difference between 

 the points which distinguish species in nature, and those which 

 differentiate breeds of domestic animals or strains of cultivated 

 plants. Although we firmly agree with the last statement, we 

 draw another conclusion, namely, that different breeds of do- 

 mestic or cultivated plants are not varieties but species. An 

 inkling of this specific difference between the main breeds of 

 animals is shown by the breeders, who persistently look for 

 many different wild species as the progenitors of these breeds, 

 In another chapter we have tried to show, in what particulars 

 the animals and plants under domestication are subjected to 

 processes and circumstances different from those among which 

 wild organisms live. The main circumstances which have differ- 

 entiated domestic breeds are a heightening of the variability" 

 of the material by cross-breeding, by a taking up of gametes, 

 genot3rpically different, an isolation, which is keeping the 

 variability of the group froin becoming equal to that of the 

 origihal one, and reducing it, and often selection, which di- 

 rects the process of automatic purification of the genotype. 

 Varieties of plants and animals under domestication may 

 quickly become species under the influence of strict isolation 

 and selection, in nature varieties are continually being swallow- 

 ed up by the species which produced them. In a species in 

 nature, in which some individuals are impure, heterozygous, 

 for a gene which has a visible influence on the development, 

 occasional individuals are produced with a new recessive char- 

 acter. All those individuals together may be termed a variety, 

 Var. niger, Var. alba. Such aberrant individuals do not consti- 

 tute a new species. They differ from the parent-species in one 

 or a few correlated characters. And again, the variability in a 

 species may be sufficient to allow of the occasional production 

 of an individual with a dominant character, developing from a 

 zygote into which two genes got together, which in combina- 

 tion produce a marked influence and not alone. Without some 



