There remains the third hypothesis, that of which I have spoken as the
hypothesis of evolution; and I purpose that, in lectures to come, we
should discuss it as carefully as we have considered the other two
hypotheses. I need not say that it is quite hopeless to look for
testimonial evidence of evolution. The very nature of the case precludes
the possibility of such evidence, for the human race can no more be
expected to testify to its own origin, than a child can be tendered as a
witness of its own birth. Our sole inquiry is, what foundation
circumstantial evidence lends to the hypothesis, or whether it lends
none, or whether it controverts the hypothesis. I shall deal with the
matter entirely as a question of history. I shall not indulge in the
discussion of any speculative probabilities. I shall not attempt to show
that Nature is unintelligible unless we adopt some such hypothesis. For
anything I know about the matter, it may be the way of Nature to be
unintelligible; she is often puzzling, and I have no reason to suppose
that she is bound to fit herself to our notions.

I shall place before you three kinds of evidence entirely based upon
what is known of the forms of animal life which are contained in the
series of stratified rocks. I shall endeavor to show you that there is
one kind of evidence which is neutral, which neither helps evolution nor
is inconsistent with it. I shall then bring forward a second kind of
evidence which indicates a strong probability in favor of evolution, but
does not prove it; and, lastly, I shall adduce a third kind of evidence
which, being as complete as any evidence which we can hope to obtain
upon such a subject, and being wholly and strikingly in favor of
evolution, may fairly be called demonstrative evidence of its
occurrence.

THE TRANSMISSION OF YELLOW FEVER BY MOSQUITOES

GEORGE M. STERNBERG, M.D., L.L.D, SURGEON-GENERAL U.S. ARMY[72]

This article is a scientific demonstration of a new fact. It shows
clearly the processes of scientific reasoning based on the methods known
to Logic as the Methods of Agreement and Difference. The theory that the
germs of the disease are carried by mosquitoes seems first to have
suggested itself to Dr. Sternberg and to Dr. Finlay through noticing a
similarity of phenomena in many cases under different conditions. Yet,
however plausible, the theory, neither of them could declare that he had
discovered the fact until the experiments carried