Plata, could destroy every individual of every species from
Southern Patagonia to Behring's Straits. What shall we say
of the extinction of the horse? Did those plains fail of
pasture, which have since been overrun by thousands and hundreds
of thousands of the descendants of the stock introduced
by the Spaniards? Have the subsequently introduced
species consumed the food of the great antecedent races?
Can we believe that the Capybara has taken the food of the
Toxodon, the Guanaco of the Macrauchenia, the existing
small Edentata of their numerous gigantic prototypes? Certainly,
no fact in the long history of the world is so startling
as the wide and repeated exterminations of its inhabitants.

Nevertheless, if we consider the subject under another
point of view, it will appear less perplexing. We do not
steadily bear in mind, how profoundly ignorant we are of the
conditions of existence of every animal; nor do we always
remember, that some check is constantly preventing the too
rapid increase of every organized being left in a state of
nature. The supply of food, on an average, remains constant, yet
the tendency in every animal to increase by propagation is
geometrical; and its surprising effects have nowhere been
more astonishingly shown, than in the case of the European
animals run wild during the last few centuries in America.
Every animal in a state of nature regularly breeds; yet in a
species long established, any _great_ increase in numbers is
obviously impossible, and must be checked by some means.
We are, nevertheless, seldom able with certainty to tell in
any given species, at what period of life, or at what period
of the year, or whether only at long intervals, the check