The fossil population of a period
is only that fraction of its living population which happened to
be buried in a certain kind of deposit under water of a certain
depth. We shall read later of insects being preserved in resin
(amber), and we have animals (and even bacteria) preserved in
trees from the Coal-forests. Generally speaking, however, the
earth has buried only a very minute fraction of its
land-population. Moreover, only a fraction of the earth's
cemeteries have yet been opened. When we further reflect that the
new type of organism, when it first appears, is a small and local
group, we see what the chances are of our finding specimens of it
in a few scattered pages of a very fragmentary record of the
earth's life. We shall see that we have discovered only about ten
skeletons or fragments of skeletons of the men who lived on the
earth before the Neolithic period; a stretch of some hundreds of
thousands of years, recorded in the upper strata of the earth.
Whatever serious difficulty there ever was in this scantiness of
intermediate types is amply met by the fact that every fresh
decade of search in the geological tombs brings some to light.
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