I remain, dear Sir, yours very faithfully, CHARLES DARWIN.
[The two following letters are also of interest as bearing on my father's views on the action of isolation as regards the origin of new species:]
CHARLES DARWIN TO K. SEMPER. Down, November 26, 1878.
My dear Professor Semper,
When I published the sixth edition of the 'Origin,' I thought a good deal on the subject to which you refer, and the opinion therein expressed was my deliberate conviction. I went as far as I could, perhaps too far in agreement with Wagner; since that time I have seen no reason to change my mind, but then I must add that my attention has been absorbed on other subjects. There are two different classes of cases, as it appears to me, viz. those in which a species becomes slowly modified in the same country (of which I cannot doubt there are innumerable instances) and those cases in which a species splits into two or three or more new species, and in the latter case, I should think nearly perfect separation would greatly aid in their "specification," to coin a new word.
I am very glad that you are taking up this subject, for you will be sure to throw much light on it. I remember well, long ago, oscillating much; when I thought of the Fauna and Flora of the Galapagos Islands I was all for isolation, when I thought of S. America I doubted much. Pray believe me,
Yours very sincerely,
CH. DARWIN.
P.S.—I hope that this letter will not be quite illegible, but I have no amanuensis at present.
CHARLES DARWIN TO K. SEMPER. Down, November 30, 1878.