From A. R. Wallace   [27 September 1857]¹

of May last, that my views on the order of succession of species were in accordance with your own, for I had begun to be a little disappointed that my paper had neither excited discussion nor even elicited opposition.² The mere statement & illustration of the theory in that paper is of course but preliminary to an attempt at a detailed proof of it, the plan of which I have arranged, & in part written, but which of course requires much ⁠⟨⁠research in English⁠⟩⁠ libraries & collections, a labour which I look ⁠⟨⁠missing section of unknown length⁠⟩⁠

With regard to the black Jaguars always breeding inter se,³ it is of course a point not capable of proof, but the black & the spotted animals are generally confined to separate localities, & among the hundreds & thousands of the skins which are articles of commerce I have never heard of a particoloured one having occurred. I think there is a difference of form the black being the more slender & graceful animal.