into those of proved theories; but, so long as the evidence at present adduced falls short of enforcing that affirmation, so long, to our minds, must the new doctrine be content to remain among the former—­an extremely valuable, and in the highest degree probable, doctrine; indeed, the only extant hypothesis which is worth anything in a scientific point of view; but still a hypothesis, and not yet the theory of species.

      “After much consideration, and assuredly with no bias against
     Mr. Darwin’s views, it is our clear conviction that, as the
     evidence stands, it is not absolutely proven that a group of
     animals having all the characters exhibited by species in nature,
     has ever been originated by selection, whether natural or
     artificial.  Groups having the morphological character of species,
     distinct and permanent races, in fact, have been so produced over
     and over again; but there is no positive evidence at present that
     any group of animals has, by variation and selective breeding,
     given rise to another group which was in the least degree
     infertile with the first.  Mr. Darwin is perfectly aware of this
     weak point, and brings forward a multitude of ingenious and
     important arguments to diminish the force of the objection.  We
     admit the value of these arguments to the fullest extent; nay, we
     will go so far as to express our belief that experiments,
     conducted by a skilful physiologist, would very probably obtain
     the desired production of mutually more or less infertile breeds
     from a common stock in a comparatively few years; but still, as
     the case stands at present, this little ‘rift within the lute’ is
     not to be disguised or overlooked.”—­(Westminster Review,
     1860.)

      “We should leave a very wrong impression on the reader’s mind if
     we permitted him to suppose that the value of Darwin’s work
     depends wholly on the ultimate justification of the theoretical
     views which it contains.  On the contrary, if they were disproved
     to-morrow, the book would still be the best of its kind—­the most
     compendious statement of well-sifted facts bearing on the
     doctrine of species that has ever appeared.  The chapters on
     variation, on the struggle for existence, on instinct, on
     hybridism, on the imperfection of the geological record, on
     geographical distribution, have not only no equals, but, so far
     as our knowledge goes, no competitors, within the range of
     biological literature.  And viewed as a whole, we do not believe
     that, since the publication of Von Baer’s Researches on
     Development, thirty years ago, any work has appeared calculated
     to exert so large an influence, not only on the future of
     biology, but in extending the domination of science over regions
     of thought into which she has, as yet, hardly
     penetrated.”—­(Ibid.)