theory of the planetary motions," [he steadfastly refused to be an
advocate of the theory,] "if by an advocate is meant one whose business
it is to smooth over real difficulties, and to persuade when he cannot
convince."

[In common fairness he warned his audience of the one missing link in
the chain of evidence--the fact that selective breeding has not yet
produced species sterile to one another. But it is to be adopted as a
working hypothesis like other scientific generalisations,] "subject to
the production of proof that physiological species may be produced by
selective breeding; just as a physical philosopher may accept the
undulatory theory of light, subject to the proof of the existence of the
hypothetical ether; or as the chemist adopts the atomic theory, subject
to the proof of the existence of atoms; and for exactly the same
reasons, namely, that it has an immense amount of prima facie
probability; that it is the only means at present within reach of
reducing the chaos of observed facts to order; and lastly, that it is
the most powerful instrument of investigation which has been presented
to naturalists since the invention of the natural system of
classification, and the commencement of the systematic study of
embryology."

[As for the repugnance of most men to admitting kinship with the apes,]
"thoughtful men," [he says,] once escaped from the blinding influences
of traditional prejudices, will find in the lowly stock whence man has
sprung the best evidence of the splendour of his capacities; and will
discern, in his long progress through the past, a reasonable ground of
faith in his attainment of a nobler future."

[A simile, with which he enforced this elevating point of view, which