cent._

The historical retrospect of the Darwinian theories, from their purely
scientific side, leads us of itself to a critical review of their present
state. We can briefly indicate in advance the result to which it will lead
us, viz.: that the descent theory has gained, the selection theory has lost
ground, the theory of development oscillates between both; but that all
three theories have not yet passed beyond the rank of hypotheses, although
they have very unequal hypothetical value. We can best arrange our review
by beginning with that theory which is the most common, and which perhaps
may still have value when both the others find their value diminished or
lost: _the theory of descent_. From that we proceed to the _theory of
evolution_, and from this to that of _selection_.

The theory of descent is indeed at first sight exceedingly plausible, and
will probably always be the _directive_ for all future investigations as to
the origin of species. The organic species show, besides the great variety
of their characteristics and the unchangeable nature of these
characteristics, many other qualities which are common to them; and these
common characteristics are precisely those which are most essential. {62}
Moreover the higher the structure of the organisms which are
differentiated, the more numerous and more valuable will become the
evidences of similarity, and the greater also will be their distance from
the inorganic and from the lowest organisms of their class, their type, or
their kingdom. For instance, rose and apple-tree, elder and ash, wolf and
dog, goat and sheep, ape and man, are not only a great deal farther removed
from the mode of existence of inorganic bodies than the algae, the monera,
and other low organisms, but they have also, in spite of the great interval
which separates them from one another and especially which separates man
from every animal, much more numerous and important points of contact than,
for instance, two families or genera of algae or of mosses, of polyps or of
infusoria, have among one another. Now our imagination refuses to accept
the theory that the Creator, or nature, or whatever we wish to call the
principle generating the species, in producing the new species, laid aside
all those points of contact which are continually becoming more numerous
and more important, and produced instead, by ever widening leaps, the new
and higher species from the inorganic, which lies farther and far