My dear Sir

I hope that you will excuse me for venturing to make a suggestion to you which I am perfectly well aware it is a very remote chance that you would adopt— I do not know whether you have read my Origin of Species   in that book I have made the remark, which I apprehend will be universally admitted that as a whole the fauna of any formation is intermediate in character between that of the formations above and below.¹ But several really good judges have remarked to me how desirable it would be that this should be exemplified and worked out in some detail, and with some single group of beings. Now every one will admit that no one in the world could do this better than you with Brachiopods.² The result might turn out very unfavourable to the views which I hold; if so, so much the better for those who are opposed to me—

But I am inclined to suspect that on the whole it would be favourable to the notion of descent with modification; for about a year ago M^r Salter in the Museum in Jermyn Street glued on a board some Spirifers &c. from 3 palæozoic stages and arranged them in single and branching lines with horizontal lines marking the formations (like the diagram in my Book if you know it) and the result seemed to me very striking though I was too ignorant fully to appreciate the lines of affinities.³   I longed to have had these shells engraved, as arranged by M^r Salter, and connected by dotted lines, and would have gladly paid the expense, but I could not persuade M^r Salter to publish a little paper on the subject  

I can hardly doubt that many curious points would occur to anyone thoroughly instructed in the subject, who would consider a group of beings under this point of view of descent with modification   All those forms which have come down from an ancient period very slightly modified ought, I think to be omitted and those forms alone considered which have undergone considerable change at each successive epoch. My fear is whether Brachiopods have changed enough. The absolute amount of difference of the forms in such groups at the opposite extremes of time ought to be considered; and how far the early forms are intermediate in character between those which appeared much later in time— The Antiquity of a group is not really diminished, as some seem vaguely to think, because it has transmitted to the present day closely allied forms. Another point is how far the succession of each genus is unbroken from the first time it appeared to its extinction with due allowance made for formations poor in fossils.

I cannot but think that an important essay (far more important than a hundred literary Reviews) might be written by one like yourself and without very great labour—⁴ I know it is highly probable that you may not have leisure, or not care for or dislike the subject, but I trust to your kindness to forgive me for making this suggestion.   If by any extraordinary good fortune you were inclined to take up this notion—I would ask you to read my Chap X on Geological Succession— And I should like in this case to be permitted to send you a Copy of a new Edit just published, in which I have added & corrected somewhat in Ch IX and X.⁵

Pray excuse this long letter and believe me | My dear Sir, | Yours very faithfully | Charles Darwin.—

I write so bad a hand I have had this note copied.—