THE PHILOSOPHY OF BIRDS' RESTS. 219 



good, sometimes distinctly, sometimes more obscurely 

 apparent, according as the habits of the species are 

 more marked, or their structure more peculiar. It 

 is true that, among birds differing but little in struc- 

 ture or habits, we see considerable diversity in the 

 mode of nesting, but we are now so well assured that 

 important changes of climate and of surface have oc- 

 cured within the period of existing species, that it 

 is by no means difficult to see how such differences 

 have arisen. Simple habits are known to be here- 

 ditary, and as the area now occupied by each species 

 is different from that of every other, we may be sure 

 that such changes would act differently upon each, and 

 would often bring together species which had acquired 

 their peculiar habits in distinct regions and under 

 different conditions. 



How do Young Birds learn to Build their First Nest? 



But it is objected, birds do not learn to make their 

 nest as man does to build, for all birds will make 

 exactly the same nest as the rest of their species, even if 

 they have never seen one, and it is instinct alone that 

 can enable them to do this. JSTo doubt this would be 

 instinct if it were true, and I simply ask for proof 

 of the fact. This point, although so important to the 

 question at issue, is always assumed without proof, and 

 even against proof, for what facts there are, are op- 

 posed to it. Birds brought up from the egg in cages 

 do not make the characteristic nest of their species, 

 even though the proper materials are supplied them, 



