140 HYPOTHESIS OF THE DEVELOPMENT OF 



The fecundity of nature has ordained that her creatures shall 

 ever be pressing upon the verge of the local means of subsist-. 

 ence. 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 appe- 

 tency which occur in all tribes ; thus exposing themselves to 

 new influences, and ceasing to experience those formerly ope- 

 rating, until, by slow degrees, in the course of a vast space of 

 time, the characters of the pheasant tribes were evoked. ( 69 ) 

 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 popu- 

 lation continually pressing behind. Altogether, this presents 

 a very different view of varieties from that which is commonly 

 presented, when we see a single peculiar individual standing 

 in the midst of, and necessarily allying itself to, the original 

 stock. The process of variation as a consequence of changed 

 conditions and appetencies being left unchecked, and that for 

 a vast space of time, we obtain at length creatures fixedly 

 peculiar ; that is, however, merely creatures which appear so, 

 because there is no replacing them in the former conditions 

 in this densely-peopled globe, and, though there were, the 

 retrogression to the anterior forms would require a space of 

 time beyond the range of human observation. 



It may now be remarked, that, in this hypothetic variabi- 

 lity, the possibility of re-union may, and in all probability 

 does, depend upon the degree of similarity which still exists 

 in the different individuals, supposing them to be members of 

 the same stirps or line of being, for I believe that no others 

 are capable of intermixture. As has been remarked by a 

 venerable naturalist " Many bulbous roots that have been 

 increased during a long succession of years by offsets, become 

 absolutely incapable of bearing seed ; 'and it is not more 

 strange that plants which in different soils and climates have 

 diverged from the original form of the first created individual, 



