190 



CHARLES DARWIN 



it would be difficult to point out any just distinction 13 

 between a species destroyed by man or by the increase of its 

 natural enemies. The evidence of rarity preceding extinc- 

 tion, is more striking in the successive tertiary strata, as 

 remarked by several able observers ; it has often been found 

 that a shell very common in a tertiary stratum is now most 

 rare, and has even long been thought to be extinct. If then, 

 as appears probable, species first become rare and then 

 extinct — if the too rapid increase of every species, even the 

 most favoured, is steadily checked, as we must admit, though 

 how and when it is hard to say — and if we see, without the 

 smallest surprise, though unable to assign the precise reason, 

 one species abundant and another closely allied species rare 

 in the same district — why should we feel such great aston- 

 ishment at the rarity being carried a step further to extinc- 

 tion ? An action going on, on every side of us, and yet barely 

 appreciable, might surely be carried a little further, without 

 exciting our observation. Who would feel any great sur- 

 prise at hearing that the Magalonyx was formerly rare com- 

 pared with the Megatherium, or that one of the fossil mon- 

 keys was few in number compared with one of the now 

 living monkeys? and yet in this comparative rarity, we 

 should have the plainest evidence of less favourable condi- 

 tions for their existence. To admit that species generally 

 become rare before they become extinct — to feel no surprise 

 at the comparative rarity of one species with another, and 

 yet to call in some extraordinary agent and to marvel greatly 

 when a species ceases to exist, appears to me much the same 

 as to admit that sickness in the individual is the prelude 

 to death — to feel no surprise at sickness — but when the sick 

 man dies to wonder, and to believe that he died through 

 violence. 



u See the excellent remarks on this subject by Mr. Lyell, in his Principles 

 of Geology. 



