LUTHER BURBANK 



essentials of size and form and function. Indeed, 

 a certain range of such variations is considered 

 to be absolutely normal. 



One would never state, for example, that any 

 particular bird has a wing or beak or tail of 

 precisely a given length; instead of this the 

 ornithologist records the average or mean length, 

 or the limits of variation shown by different 

 specimens. 



And it is universally recognized, since Darwin 

 gave us the clue, that the building up of new 

 species must be brought about through the selec- 

 tion of favorable variations. A bird with an extra 

 long wing, for example, might be able to fly a 

 little faster and secure its insect prey with greater 

 facilitj' than its fellows; and this slight advantage 

 might be instrumental in saving the life of such a 

 bird, and thus enable it to transmit its peculiarity 

 to offspring that would constitute a long-winged, 

 swift-flying race. 



Take the following incident as a tangible 

 illustration : 



In the summer of 1904 it chanced that there 

 was a severe drought in New England and there 

 were entire regions in which the insects upon 

 which the common house martin feeds failed to 

 be hatched at the usual time. The result was 

 that there was dearth of food for the martins, and 



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