156 HYPOTHESIS OF THE DEVELOPMENT OF 



an observable parallax. As there was no observed parallax, 

 because the earth's orbit is an insignificant space in comparison 

 with the distance of the stars, so is our observation of animal 

 changes insufficient to show transitions of species in the higher 

 grades of the kingdom, because it is a mere span in comparison 

 with the vast ages actually concerned in the phenomenon. 



A similar principle of explanation applies to the alleged ten- 

 dency of variety to be obliterated. While it is only to be ex- 

 pected that a single animal showing an originality of form will 

 fail to impress it on its posterity, if it be absorbed in alliance 

 with animals possessing no such peculiarities, there is no 

 reason to believe that a variety uniting with a creature like 

 itself will not have descendants of its own character. We judge 

 on this question in the midst of a fully-peopled world ; but we 

 must cast back our minds to a time when it was only in the 

 course of being filled with living things. We must think of a 

 time when, for example, over large portions of the surface 

 mountain tracts were rising, perhaps beside low and marshy 

 grounds, or when forests began to spread over extensive 

 regions. Here a new field of existence is presented. The 

 fecundity of nature has ordained that her creatures shall ever 

 be pressing upon the verge of the local means of subsistence. 

 A colonizing principle accordingly comes into play. On such 

 an occasion, it might be that individual wading birds began to 

 advance into dry grounds and woods, elected to the new life 

 perhaps by some of those varieties of appetency which occur 

 in all tribes ; thus exposing themselves to new influences, and 

 ceasing to experience those formerly operating, until, by slow 

 degrees, in the course of a vast space of time, the characters of 

 the pheasant tribe were evoked. 1 Here, it will be at once 

 perceived, re-absorption of peculiarities was not likely to occur ; 

 for the field of colonization, so to speak, was sufficiently wide 

 to allow of the new families wandering farther and farther 

 away from the original grounds and the ancestral tribes, while 

 return was prevented by the full population continually pressing 

 behind. Altogether, this presents a very different view of varieties 



1 A correspondent states that he has seen a variety of the goldfinch 

 marked by strong distinguishing characters, considerably larger size, 

 more graceful form, and much richer and more lustrous plumage, 

 which, bird-catchers say, occurs frequently as a progeny of the ordinary 

 bird. The distinctions of this animal are greater than those held in 

 many instances as specific ; there seems no room to doubt in such an 

 instance that pairs so peculiar might, in fresh ground of their own, give 

 rise to a race which naturalists would call a separate species. 



