No one will imagine that a drought, even far severer than those which cause such losses in the provinces of La 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 organised 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.