pe he can.

[Footnote a: P. 484, Engl. ed. In the new American edition, (_Vide_
Supplement, pp. 431, 432,) the principal analogies which suggest the
extreme view are referred to, and the remark is appended,--"But this
inference is chiefly grounded on analogy, and it is immaterial whether
or not it be accepted. The case is different with the members of each
great class, as the Vertebrata or Articulata; for here we have in the
laws of homology, embryology, etc., some distinct evidence that all have
descended from a single primordial parent."]

[Footnote b: In _Bibliotheque Universelle de Geneve_, Mars, 1860.]

[Footnote c: This we learn from his very interesting article, _De
la Question de l'Homme Fossile_, in the same (March) number of the
_Bibliotheque Universelle_.]

This raises the question, Why does Darwin press his theory to these
extreme conclusions? Why do all hypotheses of derivation converge so
inevitably to one ultimate point? Having already considered some of the
reasons which suggest or support the theory at its outset,--which may
carry it as far as such sound and experienced naturalists as Pictet
allow that it may be true,--perhaps as far as Darwin himself unfolds
it in the introductory proposition cited at the beginning of this
article,--we may now inquire after the motives which impel the theorist
so much farther. Here proofs, in the proper sense of the word, are not
to be had. We are beyond the region of demonstration, and have duly
probabilities to consider. What are these probabilities? What work
will this hypothesis do to establish a claim to be adopted in its
completeness? Why should a theory which may plausibly enough account for
the _diversification_ of the species of each special type or genus,
be expanded into a general system for the _origination_ or successive
diversification of all species, and all special types or forms, from
four or five remote primordial forms, or perhaps from one? We accept the
theory of gravitation because it explains all the facts we know, and
bears all the tests that we can put it to. We incline to accept the
nebular hypothesis, for similar reasons; not because it is proved,--thus
far it is wholly incapable of proof,--but because it is a natural
theoretical deduction from accepted physical laws, is thoroughly
congruous with the facts, and because its assumption serves to connect
and harmonize these into one probable and consistent whole. Can the
derivative hypothesis