evolution or selection theory; and, on the
other hand, that which seemed opposed to the selection theory was often
held to be a weakening of the evolution and descent theory; and this was
done, not only by amateurs, but often enough by the highest authorities
also. In reality, however, it is quite conceivable that the idea of a
descent may prove correct, and possibly the idea of an evolution of the
species will have to be replaced by that of a heterogenetic generation, or
by the theory that certain groups in the organic system are originated {29}
by heterogenetic generation, and others by evolution; and so the evolution
theory must share with the theory of heterogenetic generation, or of a
metamorphosis of germs. On the other hand, it is conceivable that even
where the evolution theory is confirmed, the evolution can be accounted for
wholly or partly by other reasons than those derived from the selection
theory. And even this result of present investigations is not
inconceivable: that the reasons for and against the different theories will
be found to balance one another to such a degree that they will sooner or
later lead science, in answering the question of the origin of species, to
the old confession of Socrates--"_Ignoramus_."

We shall, therefore, have to arrange our historical sketch according to the
historical order of the appearance of the theories, and treat the problems
more or less as an undivided whole. But we shall keep in mind, during our
historical sketch, not only the logical separation of the problems in
question, in order not to lose clearness of judgment, but we shall also at
the end of our review, if we consider the present condition of the
problems, have to examine the same once more in detail, so far as regards
the above mentioned separation.

* * * * *

{30}

CHAPTER I.

RISE OF THE DARWINIAN THEORIES.

Sec. 1. _Direct Predecessors.--Lamarck._

The first man who gave direct expression to the idea of a successive
generation of the species through transmutation, and who attempted to
follow it up in a scientific way, was the French naturalist and
philosopher, Jean Lamarck, born 1744. In the year 1801, and subsequently,
he published his views, first in smaller essays and afterward more in
detail in his "_Philosophie Zoologique_," which appeared in 1809, and in
the first volume of his "_Histoire Naturelle des Animaux sans Vertebres_,"
published in 1815. In thes