HI A^ARI ABILITY OF SPECIES IN A STATE OF NATURE 81 



naturalists of the old school, and all mere collectors, were 

 interested in species in proportion to their rarity, and would 

 often have in their collections a larger number of specimens 

 of a rare species than of a species that was very common. 

 Now as these rare species do really vary much less than the 

 common species, and in many cases hardly vary at all, it was 

 very natural that a belief in the fixity of species should 

 prevail. It is not, however, as we shall see presently, the 

 rare, but the common and widespread species which become 

 the parents of new forms, and thus the non-variability of any 

 number of rare or local species offers no difficulty whatever in 

 the way of the theory of evolution. 



Conclvding Bemarh. 



We have now sho^^Ti in some detail, at the risk of being 

 tedious, that individual variability is a general character of all 

 common and ^\^despread species of animals or plants ; and, 

 further, that this variability extends, so far as we know, to 

 every part and organ, whether external or internal, as well as 

 to every mental faculty. Yet more important is the fact that 

 each part or organ varies to a considerable extent inde- 

 pendently of other parts. Again, we have shown, by abundant 

 evidence, that the variation that occurs is very large in 

 amount — usually reaching 10 or 20, and sometimes even 25 

 per cent of the average size of the varying part; while 

 not one or two only, but from 5 to 10 per cent of the speci- 

 mens examined exhibit nearly as large an amount of variation. 

 These facts have been brought clearly before the reader by 

 means of numerous diagrams, drawn to scale and exhibiting 

 the actual variations in inches, so that there can be no pos- 

 sibility of denying either their generality or their amount. 

 The importance of this full exposition of the subject will be 

 seen in future chapters, when Ave shall freciuently have to 

 refer to the facts here set forth, esj^ecially when we deal with 

 the various theories of recent writers and the criticisms that 

 have been made of the Darwinian theory. 



A full exposition of the facts of variation among wild 

 animals and plants is the more necessary, because compara- 

 tively few of them were published in Mr. Darwin's works, 

 while the more important have only been made known since 



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