From [C. P.]¹   29 April 1864

Sir—

I perhaps need not apologise for troubling you with one or two suggestions occurring to me, on re-reading your book on the ‘origin of Species’,² as I am well aware of your honest love of truth, and the unusual opportunities you have enjoyed of obtaining a varied knowledge of specific forms;—yet in stating your hypothesis, it seems to me at least, that you scarcely appreciate at their full value, two disturbing causes or forces, which must operate to retard, or even to neutralise in many cases that mode of action, which you conceive to have originated mutation of specific forms and which must have equally operated to protect the individuality of species, through all time; the first being the extreme uncertainty which must have attended the transmission of an acquired peculiarity by the neutralising effect of the first modification generating with an unmodified form, and so causing a step of ‘progress’ to be diminished or annihilated;—and 2^nd. the tendency of every species to elude excessive, or superior competition, by seeking a habitat favourable to its own normal growth, for if it accidentally intrudes on an area where developement becomes unduly luxuriant (I speak now particularly of vegetable life) it is sure to be encountered by others having greater vigour from greater adaptibility, and when it enters an unfavourable or barren locality, it is diminished in growth, and circumscribed in extent by physical conditions, as, for example Epilobium tetragonum immediately occupies here heavy damp soil which is at all neglected, & flourishes beyond measure, but if the neglect be carried forth, is driven to drier banks & stone walls, by the competition of Ranunculus repens, & coarse grasses, which cannot follow it—

Competition of a species with itself is checked not only or principally by hostile action from without, but by weakness, and disease within, and in such cases as the rat & rabbit by the tendency to devour its own offspring

But your proposition if true will of course include and explain all objections, nor do I think it is strengthened or weakened by specific instances alleged by yourself, or objections of the same sort by others: the extreme variability of the Pigeon and Rabbit among vertebrates, and of Pelargonium, Calceolaria, Rubus, Rosa among plants can only be maintained by the most careful artificial treatment, and, abandoned to natural conditions of soil & exposure, revert to their types, & are examples of the luxury, not of the economy of nature—

I have thought that the first germ of your idea, or its most apparent confirmation was derived from the Geospizæ of the Galapagos, but you do not cite them in your ‘origin’, though they must have struck you powerfully in your Naturalists voyage—³

I have written solely from a love of truth, without any mere desire to criticise, and am totally indifferent to any reputation as a Naturalist, though I have long enjoyed the unutterable delight of Naturalistic Studies—

[C. P].