Among the great and fertile scientific conceptions which have either
originated or become firmly established during the nineteenth century,
the theory of evolution, if not the greatest of them all, will
certainly take its place in the front rank. As a partial explanation
(for no complete explanation is possible to finite intelligence) of the
phenomena of nature, it illuminates every department of science, from
the study of the most remote cosmic phenomena accessible to us to that
of the minutest organisms revealed by the most powerful microscopes;
while upon the great problem of the mode of origin of the various
forms of life—long considered insoluble—it throws so clear a light
that to many biologists it seems to afford as complete a solution, in
principle, as we can expect to reach.