224 STRA Y FEA THERS FROM MANY BIRDS. 



them for good or for harm. So constituted are all living 

 organisms that the minutest advantage is quickly seized 

 upon, whilst the least important change affecting them 

 unfavourably may soon become disastrous to an entire 

 race. The causes which have brought about the extinc- 

 tion of species are almost endless. We can form only 

 the very faintest idea of the agencies by which many 

 forms have been removed even in comparatively recent 

 times ; and when we go back further into the past the 

 causes of extinction are absolutely beyond the estima- 

 tion of all human intelligence. We know that during 

 the past history of the earth, millions upon millions of 

 species must have had their birth and death the multi- 

 tudinous causes of these vast phenomena are unknown 

 to man, and must ever remain so. Unfortunately for 

 science there were no Darwins living in those remote 

 ages to chronicle the wonders of a changing Universe, 

 or to reduce the majestic phenomena to law, and leave a 

 record of the wonderful process of prehistoric evolution 

 to posterity. 



It is a universal law of nature that when a species 

 becomes, in no matter how small a degree, out of har- 

 mony with the conditions of its existence, that species 

 must surely perish, or in adapting itself to those 

 changed circumstances it becomes so modified that 

 sooner or later a new race or even several races are 

 evolved, formed of those surviving individuals and their 



