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248 THEORETICAL BIOLOGY 



Through Mendel we have learnt about the distribution of 

 the parental genes to the offspring. But the laws accord- 

 ing to which the parents find one another in order to effect 

 this distribution have as yet been little studied. It is here 

 that sexual selection, so-called, plays its important part. As 

 Darwin showed, the breeder can step in in place of natural 

 selection, and produce new races and peoples within a species. 

 These artificial races play the determining role in the case 

 of our domestic animals and plants. We may still expect 

 great results from work in this direction. 



Artificial races enter our human surrounding-world in 

 a way that is conformable with plan. We are as yet without 

 the fundamental clue as to the r61e which natural selection 

 plays in the life of the individual species ; but we can be 

 certain that some day, when we have learnt to look more 

 closely into the surrounding-world of the species, our eyes 

 will be opened to plan here also. 



THE GENUS 



The genus does not represent a connection between 

 families. Nevertheless, it is not considered as a mere human 

 means to classification, but as a true product of Nature. We 

 assume that the genus depends on the relationship of species 

 one with another. Now relationship can be based only on 

 the family. 7 Therefore we assume that, countless years ago, 

 separate offspring arose from one family, which so differed 

 from one another that they no longer crossed, and in this 

 way they established new species. As an analogy, the forma- 

 tion of races is cited, although all that we can as yet establish 

 is that certain groups belonging to a common genotype within 

 the species display a tendency to separate. But, so far, 

 absolutely nothing has been discovered concerning a common 

 derivation of the species from one pair of sample animals. 



