he ey eee ee 
Miscellaneous. 375 
theory will very well account for the origination by divergence of 
nearly related species, whether within the present period or in remoter 
geological times,—a very natural view for him to take, since he appears 
to haye reached and published, several years ago, the pregnant con- 
- clusion that there most probably was some material connexion be- 
tween the closely related species of two successive faunas, and that 
the numerous close species, whose limits are so difficult to determine, 
were not all created distinct and independent. But while accepting, 
or ready to accept, the basis of Darwin’s theory and all its legitimate 
direct inferences, he rejects the ultimate conclusions, brings some 
weighty arguments to bear against them, and is evidently convinced 
that he can draw a clear line between the sound inferences which he 
fayours, and the unsound or unwarranted theoretical deductions 
which he rejects. We hope he can. 
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 con- 
sidered 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 begin- 
ning of this article,—we may now inquire after the motives which 
impel the theorist so much further. Here proofs, in the proper 
sense of the word, are not to be had. We are beyond the region of 
demonstration, and have only 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 inca- 
pable 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 
be maintained and carried out into a system on similar grounds? If 
so, however unproved, it would appear to be a tenable hypothesis, 
which is all that its author ought now to claim. Such hypotheses 
as from the conditions of the case can neither be proved nor disproved 
by direct evidence or experiment are to be tested only indirectly, 
and therefore imperfectly, by trying their power to harmonize the 
known facts, and to account for what is otherwise unaccountable, 
So the question comes to this—What will an hypothesis of the deri- 
vation of species explain which the opposing view leaves unexplained ? 
Questions these which ought to be entertained before we take up 
the arguments which have been advanced against this theory, We 
