But to illustrate. You allow that the evolutionary pedigree of the horse is made out. But what had “Natural Selection” to do with the making this out? It would have been all the very same, both the evidence and the ground of the inference, if Natural Selection had never been propounded. There is no evidence how the forms were selected, there is simply the _fact_ of the series of forms, which, with other like evidence, brings conviction to most naturalists that one has somehow come from the other. And this conviction is about as strong to those who do not believe “Natural Selection” will explain it, as those who do. 2. Professor Guyot, you mean. Dana avowedly adopts from Guyot. 3. To those who talk or think of necessary evolution, or, like Spencer, deduce it ex necessitate rei, this matter of immense time is very pertinent. I don’t think Darwin is bothered by it much. On my way of thinking, it is no bother at all, considering what a deal of time there has been anyway. 4. Do you mean “hybrid forms”? I fail to see what hybrids, that is, mules from the crossing of related species, has to do with it, one way or the other. Nobody (of clear conceptions) supposes new species come from the mixture of other species. That is a way to confuse or blend species, not to originate them. But there is no “want of hybrids;” there are plenty of them, and they have mixed some few species (dogs, for instance); but they play no important part in the matters you are considering. “Want of connecting forms in living species,” that is to the purpose. Well, as a systematic botanist, I wish there was a _want_. The connecting forms are my _great trouble_ every day. You would save me an awful deal of trouble, time, and constant uncertainty, if you would cause them to be wanting! 5. So you will not accept the motto “ex uno disce omnes.” If you admit the horse’s evolution as proved, does not that carry an implication of evolution in other lines, of which similar, but fewer steps are known? Or are all evolutions those of cavalry? CAMBRIDGE, June 17, 1862. DEAR BRACE,--Thanks for the “World.” Who wield its destinies? It is, I suppose, your article on Darwin, a very good one, for its purpose and space. Before you too confidently reject the evidence for the existence of man in the diluvial period, just turn over a very impartial and good article by Pictet,--a good judge of such matters,--in the March number of the “Bibliothèque Universelle de Genève,” “De la Question sur l’Homme Fossile.” I presume it is in the Astor Library. If it is not, you may tell Mr. Cogswell there might as well not be any Astor Library. Ever thine, A. GRAY. CAMBRIDGE, April 22, 1862 (?) DEAR BRACE,--You are very welcome to such casual criticism as I can offer on your two pages of manuscript.