DIFFICULTIES OF THE THEORY 249 



is nearly as aquatic as the coot, and the second nearly 

 as terrestrial as the quail or partridge. In such cases, 

 and many others could be given, habits have changed 

 without a corresponding change of structure. The 

 webbed feet of the upland goose may be said to 

 have become almost rudimentary in function, though 

 not in structure. In the frigate-bird, the deeply scooped 

 membrane between the toes shows that structure has 

 begun to change. 



He who believes in separate and innumerable acts of 

 creation may say, that in these cases it has pleased the 

 Creator to cause a being of one type to take the place 

 of one belonging to another type; but this seems to me 

 only restating the fact in dignified language. He who 

 believes in the struggle for existence and in the principle 

 of natural selection will acknowledge that every organic 

 being is constantly endeavoring to increase in numbers; 

 and that if any one being varies ever so little, either 

 in habits or structure, and thus gains an advantage over 

 some other inhabitant of the same country, it will seize 

 on the place of that inhabitant, however diflEerent that 

 may be from its own place. Hence it will cause him no 

 surprise that there should be geese and frigate-birds with 

 webbed feet, living on the dry land and rarely alighting 

 on the water; that there should be long-toed corncrakes, 

 living in meadows instead of in swamps; that there 

 should be woodpeckers where hardly a tree grows; that 

 there should be diving thrushes and diving Hymenoptera, 

 and petrels with the habits of auks. 



