144 THE ORIGIN OF SPECIES 



elude that transitional states between structures fitted for very dif- 

 ferent habits of life will rarely have been developed at an early 

 period in great numbers and under many subordinate forms. Thus, 

 to return to our imaginary illustration of the flying-fish, it does 

 not seem probable that fishes capable of true flight would have 

 been developed under many subordinate forms, for taking prey of 

 many kinds in many ways, on the land and in the water, until their 

 organs of flight had come to a high stage of perfection, so as to 

 have given them a decided advantage over other animals in the 

 battle for life. Hence the chance of discovering species with transi- 

 tional grades of structure in a fossil condition will always be less, 

 from their having existed in lesser numbers, than in the case of 

 species with fully developed structures. 



I will now give two or three instances, both of diversified and 

 of changed habits, in the individuals of the same species. In either 

 case it would be easy for natural selection to adapt the structure 

 of the animal to its changed habits, or exclusively to one of its 

 several habits. It is, however, difficult to decide and immaterial for 

 us, whether habits generally change first and structure afterward; 

 or whether slight modifications of structure lead to changed habits ; 

 both probably often occurring almost simultaneously. Of cases of 

 changed habits it will suffice merely to allude to that of the many 

 British insects which now feed on exotic plants, or exclusively on 

 artificial substances. Of diversified habits innumerable instances 

 could be given: I have often watched a tyrant flycatcher (Sauro- 

 phagus sulphuratus) in South America, hovering over one spot and 

 then proceeding to another, like a kestrel, and at other times stand- 

 ing stationary on the margin of water, and then dashing into it 

 like a kingfisher at a fish. In our own country the larger titmouse 

 (Parus major) may be seen climbing branches, almost like a 

 creeper; it sometimes, like a shrike, kills small birds by blows on 

 the head; and I have many times seen and heard it hammering 

 the seeds of the yew on a branch, and thus breaking them like a 

 nuthatch. In North America the black bear was seen by Hearne 

 swimming for hours with widely open mouth, thus catching, almost 

 like a whale, insects in the water. 



As we sometimes see individuals following habits different from 

 those proper to their species and to the other species of the same 

 genus, we might expect that such individuals would occasionally 

 give rise to new species, having anomalous habits, and with their 

 structure either slightly or considerably modified from that of their 

 type. And such instances occur in nature. Can a more striking 

 instance of adaptation be given than that of a woodpecker for 



