26 to .57. The result, it is explained, would have been not a uniform
heat or cold, but extremes of both; there would probably have been short
but very hot summers, and long and intensely cold winters.
This, Sir John Lubbock thought, might account for the co-existence of
both hot and arctic species, like the hippopotamus and rhinoceros on the
one hand, and the musk-ox and the reindeer on the other.
But such considerations really help us little. In the first place, it is
only an assumption that the fossil hippopotamus _was_ an animal of a hot
climate--it does not in any way follow from the fact that the now
existing species is such; nor if we make the assumption, does it explain
how, if the hot summer sufficed for the tropical hippopotamus, it
managed to survive the long and cold winters which suited the arctic
species.
Moreover, no such calculations can really be made with accuracy: we do
not know what other astronomical facts may have to be taken into
consideration, nor can we say when such "periods" as those which are so
graphically described, began or ended.
In this very instance, we know that the mammoth only became extinct in
comparatively recent times, since specimens have been found in Siberia,
with the hair, skin, and even flesh, entirely preserved. Granted that
the intense cold of the Siberian ice effected this, it is impossible to
admit more than a limited time for the preservation--not hundreds of
thousands of years.
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