The Making of Species 



only will the most stable biological molecules be 

 formed, but the most stable radicles will dominate 

 the molecule. Hence, if any two animals are 

 crossed and the offspring show alternate inherit- 

 ance, the resulting organism will, in the case of 

 each unit character, display the most stable of 

 the pair ; in other words, it will take after the 

 parent which happens to have the greater 

 stability as regards that particular character. 

 The difference between the mule and the hinny 

 would seem to be explicable on this supposition. 

 If the union were like a simple chemical syn- 

 thesis it should not make any difference which 

 way the cross were made. But if the species 

 crossed are of varying stability, and if their 

 respective degrees of stability vary with the sex, 

 it is easy to see that it will make a difference 

 how the animals are crossed. 



In the cases of creatures that obey Mendel's 

 law, the most stable form of a unit character will 

 presumably be the dominant one. 



One of the most curious of the phenomena of 

 inheritance is that of correlation. We shall deal 

 with this more fully in Chapter VIII. It will 

 suffice here to say that certain characters appear 

 to be linked together in organisms. Such seem 

 to be transmitted in pairs. The offspring never 

 exhibits one of such a correlated couple without 

 exhibiting the other also. 



It would thus seem that certain combinations 

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