could conceivably be brought about without the intervention of a directing
power, the riddle which animate nature presents to our intelligence at
every turn, and in face of which the mind of a Kant could find no way out,
for he regarded a solution of it as not to be hoped for. For, even if we
were to assume an evolutionary force that is continually transforming the
most primitive and the simplest forms of life into ever higher forms, and
the homogeneity of primitive times into the infinite variety of the
present, we should still be unable to infer from this alone how each of the
numberless forms adapted to particular conditions of life should have
appeared PRECISELY AT THE RIGHT MOMENT IN THE HISTORY OF THE EARTH to which
their adaptations were appropriate, and precisely at the proper place in
which all the conditions of life to which they were adapted occurred: the
humming-birds at the same time as the flowers; the trichina at the same
time as the pig; the bark-coloured moth at the same time as the oak, and
the wasp-like moth at the same time as the wasp which protects it. Without
processes of selection we should be obliged to assume a "pre-established
harmony" after the famous Leibnitzian model, by means of which the clock of
the evolution of organisms is so regulated as to strike in exact
synchronism with that of the history of the earth! All forms of life are
strictly adapted to the conditions of their life, and can persist under
these conditions alone.

There must therefore be an intrinsic connection between the conditions and
the structural adaptations of the organism, and, SINCE THE CONDITIONS OF
LIFE CANNOT BE DETERMINED BY THE ANIMAL ITSELF, THE ADAPTATIONS MUST BE
CALLED FORTH BY THE CONDITIONS.

The selection theory teaches us how this is conceivable, since it enables
us to understand that there is a continual production of what is non-
purposive as well as of what is purposive, but the purposive alone