8o THE EVOLUTION OF LIVING BEINGS. 



Now let US look into this question. 



Inside of a community of different types, originated 

 from a cross, which do not further intercross, we will 

 get, as calculated above, after a number of generations 

 a large number of species, and but comparatively few 

 heterozygotes. 



The effect of selection can therefore be nothing 

 else than a reduction of the number of species arisen, 

 by elimination of the ones less weU fitted to survive, 

 than those which are not eliminated. 



Now this is exactly what happens. 



About the effect of cold as a selector Nilsson-Ehle 

 says in the article quoted above: 



Besonders schnell degeneriren im Klima Schwedens 

 wenig winterfeste Sorten (Linneons according to our 

 nomenclature); die abweichenden Typen nehmen, 

 wenn sie winterfester als die echten sind, nach stren- 

 gen Wintem sehr rasch an Zahl zu und konnen 

 bald vorherrschend werden. Die Sorte verUert dann 

 zulezt ganzUch ihren urspriingUchen Charakter." 



Now what can be expected to happen in a freely 

 intercrossing community, say if the dominant type is 

 for some reason or other favored through extermination 

 of the recessives in proportionally greater numbers 

 than the dominants? 



Such a selection must necessarily also favor the 

 hybrids with dominant appearance because, if f . i. a 

 grey rabbit is favored, on account of its protective 

 color, such a protection is not the outcome of its 

 genotypical constitution but of its phenotj^ical as- 

 pect, and as this does not differ from that of the pure 



