TENDENCY OP SPECIES TO EORM VAEIETIES. 53 



(only few will succeed) to seize on as many and as diverse places 

 in the economy of nature as possible. Eacli new variety or species, 

 wlien formed, will generally take the place of, and thus exterminate 

 its less well-fitted parent. This I believe to be the origin of the 

 classification and affinities of organic beings at all times; for 

 organic beings always seem to branch and sub-branch like the 

 limbs of a tree from a common trunk, the flourishing and diver- 

 ging twigs destroying the less vigorous — the dead and lost branches 

 rudely representing extinct genera and families. 



This sketch is most imperfect ; but in so short a space I cannot 

 make it better. Your imagination must fill up very wide blanks. 



C. Daewin. 



III. On the Tendency of Varieties to depart indefinitely from the 

 Original Type, By Alebed Rtjssel Wallace. 



One of the strongest arguments which have been adduced to 

 prove the original and permanent distinctness of species is, that 

 varieties produced in a state of domesticity are more or less un- 

 stable, and often have a tendency, if left to themselves, to return 

 to the normal form of the parent species ; and this instability is 

 considered to be a distinctive peculiarity of all varieties, even of 

 those occurring among wild animals in a state of nature, and to 

 constitute a provision for preserving unchanged the originally 

 created distinct species. 



In the absence or scarcity of facts and observations as to 

 varieties occurring among wild animals, this argument has had 

 great weight with naturalists, and has led to a very general and 

 somewhat prejudiced belief in the stability of species. Equally 

 general, however, is the belief in what are called " permanent or 

 true varieties," — races of animals which continually propagate 

 their like, but which difier so slightly (although constantly) from 

 some other race, that the one is considered to be a variety of the 

 other. "Which is the variety and which the original species, there 

 is generally no means of determining, except in those rare cases 

 in which the one race has been known to produce an offspring 

 unlike itself and resembling the other. This, however, would 

 seem quite incompatible with the "permanent invariability of 

 species," but the difficulty is overcome by assimiing that such 

 varieties have strict limits, and can never again vary further from 

 the original type, although they may return to it, which, from the 



