My dear Hooker

I sh^d. have less scruple in troubling you, if I had any confidence what my work would turn out; sometimes I think it will be good; at other times I really feel as much ashamed of myself, as the Author of the Vestiges ought to be of himself. I know well that your kindness & friendship would make you do a great deal for me, but that is no reason that I sh^d. be unreasonable: I cannot & ought not to forget that all your time is employed in work certain to be valuable. It is superfluous in me to say that I enjoy exceedingly writing to you, & that your answers are of the greatest possible service to me.—

I return with many thanks the Proof on Aquilegia:² it has interested me much: it is exactly like my Barnacles:³ but for my particular purpose, most unfortunately both Kolreuter⁴ & Gærtner⁵ have worked chiefly on A. vulgaris & Canadensis & atro-purpurea; & these are just the species, that you seem not to have studied.— (N.B. Why do you not let me buy the Indian Flora? you are too magnificent.)⁶ With respect to splitting Australia we are in a “Muddle”; I do not think I quite understood you & you me; I am pretty sure I do not quite understand or remember what I wrote myself; & I doubt whether you quite understand or remember what you wrote; for in first letter you say “Under this view disruption produces similarity of Botanical features”: in your second letter, you say that “three-fourths would be killed, & that a greater proportion of those species common to both (islands) would be killed, than of those peculiar to each”; but this w^d. produce dis similarity.—⁷

Now for a short ride on my chief (at present) Hobby-Horse, viz aberrant genera: what you say under your remarks on Lepidodendron seems just the case, viz that I want to give some sort of evidence of what we both believe in, viz how groups come to be anomalous or aberrant. And I think some sort of proof is required; for I do not believe very many naturalists would at all admit our view. Thank you for caution on large anomalous genera first catching attention. I do not quite agree with your “grave objection to the whole process” which is “that if you multiply the anomalous species by 100, & divide the normal by the same, you will then reverse the names”… — For, to take an example, ornithoryhnchus & Echidna⁸ would not be less aberrant if each had a dozen (I do not say 100, because we have no such cases in animal kingdom) species instead of one. What would really make these 2 genera less anomalous, would be the creation of many genera & sub-families round & radiating from them on all sides. Thus if Australia were destroyed Didelphys in S. America w^d be wonderfully anomalous (this is your case with Proteaceæ—), whereas now there are so many genera & little sub-families of Marsupiata, that the group cannot be called aberrant or anomalous. Sagitta⁹ (& the Earwig) is one of the most anomalous animals in world, & not a bit the less because there are a dozen species.— Now my point (which I think is a slightly new point of view) is, if it is extinction which has made the genus anomalous, as a general rule , the same causes of extinction would allow the existence of only a few species in such genera.

Whenever we meet (which will be on 23^d. Club)¹⁰ I shall much like to hear whether this strikes you as sound; I feel all the time on the borders of a circle of truism.— Of course I could not think of such a request, but you might possibly, if Bentham does not think the whole subject rubbish, ask him sometime to pick out the dozen most anomalous genera in the Leguminosæ,¹¹ or any great order of which there is a monograph, by which I could calculate the ordinary percentage of species to genera. I am the more anxious as the more I enquire, the fewer are the cases in which it can be done: it cannot be done in Birds or I fear Mammifers. I doubt much whether in any other class of Insects.—

I saw your nice notice of poor Forbes in Gardeners Chron; & I see in Athenæum a notice of meeting on last Saturday of his friends:¹² of course I shall wish to subscribe as soon as possible to any memorial.

Farewell you most goodnatured of men. C. Darwin.—

I have just been testing practically what disuse does in reducing parts; I have made skeletons of wild & tame Duck (oh the smell of well-boiled, high Duck!!)¹³ & I find the tame-duck wing, ought according to scale of wild prototype to have its two wings 360 grams in weight, but it has it only 317 or 43 grams too little or 17^th of own two wings too little in weight: this seems rather interesting to me.—¹⁴

P.S. I do not know whether you will think this worth reading over; I have worked it out since writing my letter. & tabulated the whole.—¹⁵ diag 21 orders with 1 genus, having 7.95 species (or 4.6?)

29 orders — 2 genera, having 15.05 species on average.

23 orders each with 3 genera; & these genera include on average 8.2 species

20 orders each with 4 genera, & these genera include on average 12.2 species

27 orders each with above 50 genera (altogether 4716 genera) & these genera

on average have 9.97 species.ramme

From this I conclude whether there be many or few genera in an Order, the number of species in genus is not much affected; but perhaps when only 1 genus in order it will be affected; & this will depend whether on Erythroxylon be made a Family of.—¹⁶