262 THE STATUS OF MAN. 



parents, but a smaller number, and that in their turn, only a 

 few of their number will be parents. Automatically a species 

 purifies itself. 



In plants, the case given by Bateson, that of Lychnis diurna 

 and Vespertina, is a representative one. Hybrids are constantly 

 being produced, and they" always disappear, the old two spe- 

 cies assimilate them. 



Each species prefers a somewhat different habitat, but the 

 difference, though efficient in keeping the majority of indi- 

 viduals of each species in localities where they do not meet in- 

 dividuals of the other species, does not preclude great numbers 

 of both species to coexist in the same environment, where it 

 is neither too dry and suimy for vespertina, not too shady and 

 damp for diurna. 



In other cases, we find two or three or more species living in 

 the same environment, when they are equally well adapted to 

 this environment, and when the occasional hybrids produced 

 are perfectly fertile. In all these instances we can find some 

 influence which makes intra-specif ic matings very much more 

 frequent than inter-specific ones, e. g. autogamy. And we must 

 always remember, that the nature of the cause or causes, which 

 bring about this preponderance of intra-specific matings, is 

 immaterial. The species kept apart by it, are equally good spe- 

 cies whether the cause is a geographic barrier, an adaptation to 

 a somewhat different environment, a differential mating be- 

 cause of prejudice, or the interference of man. The different 

 species of dogs in one city, the different species of cattle in one 

 country fmrdsh beautiful examples of groups of species which 

 coexist in. one environment, which occasionally cross and yet 

 preserve their identity as species. There is no fundamental 

 difference between this cause of specific diversity and a geo- 

 graphic barrier, the so-called breeds of cattle are as good spe- 

 cies as the tree-rat and the house-rat. 



A variety is a number of individuals which all differ from 

 the species to which they belong in an identical point, without 

 having continuity. The Holstein breed of cattle constitutes a 



