From H. C. Watson 21 November 
My dear Sir
Once commenced to read the ‘Origin’ I could not rest till I had galloped through the whole. I shall now begin to re-read it more deliberately. Meantime I am tempted to write you the first impressions, not doubting that they will in the main be the permanent impressions.
1st Your leading idea will assuredly become recognized as an established truth in science, i.e. “natural selection”.— (It has the characteristics of all great natural truths, clarifying what was obscure, simplifying what was intricate, adding greatly to previous knowledge. You are the greatest Revolutionist in natural history of this century, if not of all centuries.
2d you will perhaps need in some degree to limit or modify, possibly in some degree also to extend your present applications of the principle of ‘natural selection’.— (Without going to matters of more detail, it strikes me that there is one considerable primary inconsistency, by one failure in the analogy between varieties & species; another by a sort of barrier assumed for nature on insufficient grounds, and arising from “divergence”. These may, however, be faults in my own mind, attributable to yet incomplete perception of your views. And I had better not trouble you about them before again reading the volume.1
3d — Now these novel views are brought fairly before the scientific public, it seems truly remarkable how so many of them could have failed to see their right road sooner.— (How could Sir C. Lyell, for instance, for thirty years read, write, & think, on the subject of species & their succession, & yet constantly look down the wrong road!2
A quarter century ago you & I must have been in something like the same state of mind, on the main question. But you were able to see & work out the quo modo of the succession, the all-important thing, while I failed to grasp it. I send by this post a little controversial pamplet of old date,—Combe & Scott.3 If you will take the trouble to glance at the passages scored on the margin, you will see that, a quarter century ago, I was also one of the few who then doubted the absolute distinctness of species & special creations of them. Yet I, like the rest, failed to detect the quo modo which was reserved for your penetration to discover, & by your discernment to apply.
You answered my query about the hiatus between Satyrus & Homo as was expected. The obvious explanation really never occurred to me till some months after I had read the papers in Linnean Proceedings; & I feel no doubt that its then occurrence was due to those papers.4 The first species of Fere-homo would soon make direct & exterminating war upon his Infra-homo cousins. The gap would thus be made, & then go on increasing into the present enormous & still-widening hiatus.— But how greatly this, with your chronology of animal life, will shock the ideas of many men!
very sincerely | Hewett C. Watson C. Darwin | Esqe
Believes natural selection will become recognised as an established truth in science, though it will shock the ideas of many men.
Please cite as
Darwin Correspondence Project, “Letter no. 2540,” accessed on 19 January 2017, http://www.darwinproject.ac.uk/DCP-LETT-2540