176 CAUSES OF EXTINCTION. [cuar. VIII. 
extinct. If then, as appears probable, species first become rare 
and then extinet—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—te feel no sur- 
prise at sickness—but when the sick man dies to wonder, and 
to believe that he died through violence. 
