Thanks for answer to query. “I see … that there is no hope of comparing the same genus at two different periods, and seeing whether the tendency to vary is greater at one period in such genus than at another period.”
Inclined to dispute SPW’s doctrine that islands are generally ancient. Doubts that they are remnants of continents.
Down Bromley Kent
My dear Sir
I am very much obliged to you for having taken the trouble to answer my query so fully.f1 I can now be at rest, for from what you say & from what little I remember Forbes said, my point is unanswerable. The case of Terebratula is to the point, as far as it goes, and is negative.— I have already attempted to get a solution through geographical distribution by Dr. Hooker’s means, & he finds that same genera which have very variable species in Europe, have other very variable species elsewhere. This seems the general rule, but with some few exceptions.— I see from the several reasons which you assign, that there is no hope of comparing the same genus at two different periods, & seeing whether the tendency to vary is greater at one period in such genus than at another period.— The variability of certain genera or groups of species strikes me as a very odd fact.—
I shall have no points, as far as I can remember, to suggest for your reconsideration, but only some on which I shall have to beg for a little further information.—f2 However I feel inclined very much to dispute your doctrine of islands being generally ancient in comparison, I presume, with continents. I imagine you think that islands are generally remnants of old continents, a doctrine which I feel strongly disposed to doubt— I believe them generally rising points, you, it seems, think them sinking points—f3
With many thanks | Yours very sincerely | C. Darwin