From H. C. Watson   10 May 1860

My dear Sir

I return by same post the four notices of ‘Origin’ which you kindly sent.— Gradually, the various arguments, objections, cavils, etc. on the grand subject are growing into a sort of conglomerate in my recollections; who said this, & who said that, getting pretty much confused together. I hope you can keep them mentally distinct.

Pictet goes a good way,¹—farther perhaps than he himself clearly knows,—   on page 15, where you pencil the no. 12,² your difficulty is & will be to lead zoologists & botanists, those who look to existing “species”, so far as Pictet “believes”. Until a faith in certain impassable barrier between existent species becomes thoroughly shaken, naturalists will resist your views, & hail difficulties as if conclusive arguments on the contra side.

Differently as these unseen barriers are traced or placed, they are believed in about as strongly by almost all. Let the subjoined numerals represent botanical forms, & the lines be the barriers as placed by different botanists;

Jordan³ 1 2 3 4 5 6 7 8 9 0 Babington⁴ 1 2 3 4 5 6 7 8 9 0 Bentham⁵ 1 2 3 4 5 6 7 8 9 0 Hooker⁶ 1 2 3 4 5 6 7 8 9 0 at any rate, previous to 1859.

This represents an approximate uniformity which is not always found; the differences lying only in the more numerous barriers of J e B, as compared with B e H.— But these transpositions sometimes occur;

Hooker 1 2 3 4 — One species Smith⁷ 1 2 3 4 — Two species Babⁿ. 1 4 2 3 — Two (other) species

Shall I bore you with a simple illustration of convergence?⁸ You have at any rate the option not to read it. Take two plants, nore or less unlike in all other respects than these three characters:—

1. Glabrous — Leaves linear — Flowers white. 2. Pubescent — Leaves oval — Flowers blue 1 varies with leaves lanceolate — Flowers pink. 2 varies with Leaves lanceolate — Flowers pink.

Then let one (1) become pubescent, or the other (2) glabrous; & the convergence is completed so far as the three characters go.—

Accumulate similar convergences, in your way of accumulating divergences, and though you may never actually change two distant species into each other, you still may counterpoise endless divergence. Now, as facts in nature, the changes from pubescent to glabrous,—from linear or oval to lanceolate,—from white or blue to pink,—are ordinary, & excite no surprize singly. And yet those three characters would be held (as a rule) amply sufficient to justify a separation of 1 e 2 as perfectly distinct species, tho‘ all other technical characters should agree.

I presume you would say that some ancestors of 1 e 2 had lanceolate leaves & pink flowers, which had diverged into linear & white, oval & blue. But you can at best only suppose this lanceolate & pink fore-parent. And if you try to account for all converging variations in the like manner, your original adam or dozen of adams must surely have combined every character in one? Unless you believe that diverging characters are novelties, while converging are restorations only?

Sincerely yours | Hewett C^l. Watson

C. Darwin | Es^qe