over the
whole globe. Further, it lies in the nature of the case that the strata in
mountain formations can only give a very incomplete picture of the whole
variety of the real organic life which may have populated the earth and the
sea. What a poor picture of the present plant and animal life would be
offered, for instance, by the soil of our continents, the slime, sand, and
pebbles of our coasts and of the bottoms of our lakes and seas, if we had
to construct from them alone the fauna and flora of the present! A third,
but purely hypothetical, consideration is rendered of importance
particularly by Darwin and Haeckel; namely, that the forms of transition
without doubt existed for a shorter period than those forms whose
organization has established itself in fully developed species.

Thus far we have directed our attention to inquiring how the organic
individuals were originated--and have throughout observed a successive
development; next, we have questioned geology--and here also have observed
a progress in the appearance of the species, but have received at the same
time contradictory answers to the question whether this progress presents
itself as a gradual development of one species from another or as a sudden
appearance. So the reasons for and against the evolution theory almost
balance one another; and it is not improbable that the hypothesis of an
origin of species through development will have to share its authority with
the hypothesis of a descent of species through heterogenetic generation, as
well as with the hypothesis of a primitive generation of lower organisms,
still repeating itself at a later time. Thus for the origination of {88}
groups lying nearer together, we have the evolution theory; for the other
groups, and especially for the origination of types where no transitions to
other types can be traced, the theory of the heterogenetic or primitive
generation recommends itself; and both theories thus far are of a purely
hypothetical nature.

But there is still a third realm, which is just as open to our observation
as the history of the development of organisms and as geology, and of which
we can also ask, whether it does not open for us an indirect way to the
knowledge of the origin of species, and especially of man--a knowledge
which we can no longer approach in the direct way of observation. This
realm is _natural history_ and the _history of the development of the human
race_. For mankind also is