﻿95 



VARIATION. 



Read April i^th, 1887, by T. D. A. COCKERELL. 



All the characters by which organisms are classified may 

 be supposed to have arisen in variation, and being continued 

 by transmission and fixed by natural selection, to have 

 gradually become typical of a genus, species, family, or class. 



Such peculiarities will have been, early in their history, 

 inconstant, and easily influenced by external conditions, 

 although their present condition is, in many cases, one of 

 extreme constancy, even to the extent of proving harmful or 

 absolutely destructive to the organism when new circum- 

 stances arise. 



In classification, obviously, the most valuable and im- 

 portant characters are those which have been thus fixed, so 

 that the old causes of their existence no longer influence 

 them, or are necessary for their continuance, while new 

 influences, which would perhaps have been unfavourable to 

 their production, do not now materially affect them. Hence 

 it has come to pass that most naturalists have hitherto 

 studied only such characters as are so far independent of 

 the influences that first formed them as to be constant under 

 new conditions, and sufficiently so to be taken as typical of 

 species or genera. Seeking the origin and cause of these 

 fixed characters, it is often possible to show clearly enough 

 how they are adapted to external circumstances, giving their 

 possessors advantages in the struggle for existence in many 

 ways ; and from this it may be argued with sufficient reason 

 that the cause of this or that peculiarity was the advantage 

 it gave to the species, and its development on that account 

 by natural selection. It is indeed as though one were looking 

 at a picture, knowing nothing of the method of painting, yet 

 noting how it represented familiar objects, reasoning that 

 whoever painted the picture, and however it was done, the 

 painter at least had those objects before him or in his mind 

 at the time — that his desire to imitate them, in fact, was the 

 cause of the result now seen upon the canvas. 



