176 CAUSES OF EXTIXCTIOX. [CHAP. Tin. 



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 dis- 

 trict 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 Megatherium, 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 com- 

 parative 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 sur- 

 prise at sickness but when the sick man dies to wonder, and 

 to believe that he died through violence. 



