| ↑ 5 blocks not present in 1859 1860; present in 1861 1866 1869 1872 |
| So little is this subject understood, that I have heard surprise repeatedly expressed at such great monsters as the Mastodon and the more ancient Dinosaurians having become extinct; as if mere bodily strength gave victory in the battle of life.
Mere size, on the contrary, would in some cases determine
quicker
extermination from the greater amount of requisite food.
Before man inhabited India or Africa, some cause must have checked the continued increase of the existing elephant.
A highly capable judge
believes that at the present day insects (as Bruce has likewise described in Abyssinia),
from incessantly harassing and weakening the elephant,
are one chief check to
its increase.
It is certain that insects of different kinds,
and blood-sucking bats,
determine the existence of the larger naturalised quadrupeds in several parts of S. America.
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Owen soon perceived that the tooth, though so like that of the existing horse, belonged to an extinct species. Had this horse been still living, but in some degree rare, no naturalist would have felt the least surprise at its rarity; for rarity is the attribute of a vast number of species of all classes, in all countries. If we ask ourselves why this or that species is rare, we answer that something is unfavourable in its conditions of life; but what that something is, we can hardly ever tell. On the supposition of the fossil horse still existing as a rare species, we might have felt
from the analogy of all other mammals, even of the
elephant, and from the history of the naturalisation of the domestic horse in South America, that under more favourable conditions it would in a very few years have stocked the whole continent. But we could not have told what the unfavourable conditions were which checked its increase, whether some one or several contingencies, and at what period of the
life, and in what degree, they severally acted. If the conditions had gone on, however slowly, becoming less and less favourable, we assuredly should not have perceived the fact, yet the fossil horse would certainly have become rarer and rarer, and finally extinct;— its place being seized on by some more successful competitor. |
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| It is most difficult always to remember that the increase of every
is constantly being checked by unperceived
agencies; and that these same unperceived agencies are amply sufficient to cause rarity, and finally extinction. ↑ We see in many cases in the more recent tertiary formations, that rarity precedes extinction; and we know that this has been the progress of events with those animals which have been exterminated, either locally or wholly, through
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