i8o RARITY PRECEDES EXTINCTION, [chap, viri, 



then lost : it would be difficult to point out any just distinc- 

 tion* between a species destroyed by man or by the increase 

 of its natural enemies. The evidence of rarity preceding 

 extinction, 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 astonishment at the rarity being carried 

 a step further to extinction ? 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 surprise at hearing that the 

 megalonyx was formerly rare compared with the mega- 

 therium, or that one of the fossil monkeys 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 conditions 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. 



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

 of Geology." 



