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CHAPTER X. 



WALLACE'S SECTION OF THE JOINT MEMOIR READ 

 BEFORE THE LINNEAN SOCIETY JULY 1, 1858. 



THE communication by Alfred Russel Wallace was 

 entitled " On the Tendency of Varieties to depart 

 indefinitely from the Original Type." An abstract 

 of it is given below. 



Varieties produced in domesticity are more or 

 less unstable, and often tend to return to the parent 

 form. This is usually thought to be true for all 

 varieties, and to be a strong argument for the original 

 and permanent distinctness of species. 



On the other hand, races forming " permanent 

 or true varieties" are well known, and there are 

 generally no means of determining which is the 

 variety and which the original species. The hypo- 

 thesis of a "permanent invariability of species" is 

 satisfied by supposing that, while such varieties 

 cannot diverge from the species beyond a certain 

 fixed limit, they may return to it. 



This argument is founded on the assumption 

 that varieties in nature are in all respects identical 

 with those of domestic animals. The object of the 

 paper is to show that this is false, and "that there 

 is a general principle in nature which will cause 



