Journal of Researches into the Natural History and Geology of the Countries Visited During the Voyage Round the World of H.M.S. Beagle Under · Charles Darwin
BANDA ORIENTAL AND PATAGONIA.
In the cases where we can trace the extinction of a species through man, either wholly or in one limited district, we know that it becomes rarer and rarer, and is then lost: it would be difficult to point out any just distinction[13] 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 farther to extinction? An action going on, on every side of us, and yet barely appreciable, might surely be carried a little farther without exciting our observation. Who would feel any great surprise at hearing that the Magalonyx 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 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. [13] See the excellent remarks on this subject by Mr. Lyell, in his _Principles of Geology._ Santa Cruz—Expedition up the River—Indians—Immense Streams of basaltic lava—Fragments not transported by the River—Excavation of the valley—Condor, habits of—Cordillera—Erratic boulders of great size—Indian relics—Return to the ship—Falkland Islands—Wild horses, cattle, rabbits—Wolf-like fox—Fire made of bones—Manner of hunting wild cattle—Geology—Streams of stones—Scenes of violence—Penguin—Geese—Eggs of Doris—Compound animals.
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