My dear Gray

This shall be such an extraordinary note as you have never received from me, for it shall not contain one single question or request. I thank you for your impression on my views.² Every criticism from a good man is of value to me. What you hint at generally is very very true, that my work will be grievously hypothetical & large parts by no means worthy of being called inductive; my commonest error being probably induction from too few facts.— I had not thought of your objection of my using the term “natural Selection” as an agent; I use it much as a geologist does the word Denudation, for an agent, expressing the result of several combined actions. I will take care to explain, not merely by inference, what I mean by the term; for I must use it, otherwise I sh^d. incessantly have to expand it into some such (here miserably expressed) formula as the following, “the tendency to the preservation (owing to the severe struggle for life to which all organic beings at some time or generation are exposed) of any the slightest variation in any part, which is of the slightest use or favourable to the life of the individual which has thus varied; together with the tendency to its inheritance”.³ Any variation, which was of no use whatever to the individual, would not be preserved by this process of “natural selection”. But I will not weary you by going on; as I do not suppose I c^d make my meaning clearer without large expansion.— I will only add one other sentence: several varieties of Sheep have been turned out together on the Cumberland Mountains, & one particular breed is found to succeed so much better than all the others, that it fairly starves the others to death: I sh^d. here say that natural selection picks out this breed, & would tend to improve it or aboriginally to have formed it.—⁴

Many thanks for seed & specimens of Adlumia:⁵ I must confess from what I have seen in Bees whilst sucking Fumaria, I see no difficulty whatever in Bees crossing the individuals: & I would venture to predict that it has a nectary on both sides instead of on only one side, for the sort of cap of joined petals can be pushed with equal easiness both ways, but where there is only one nectary it can be pushed (as far as I have seen) only one way: Lecoq, I observe, brings forward Fumaria as a genus which c^d never be crossed by natural means,⁶ whereas I suspect its structure is formed in direct relation to favour crossing!!⁷

I sent you Gardeners Chronicle with little notice on Kidney Beans:⁸ since writing it, I have received a most curious lot of Beans naturally crossed, & the seed-coats affected by the act of fertilisation like Gærtners Pea case.—⁹ By the way I must tell you what I heard yesterday, though not in your line, but on subject of the crossing of individuals. Barnacles (Balanus) are hermaphrodite & with their well shut up shell offer as great a difficulty to crossing as can well be conceived: I found an individual with monstrous & imperforate penis, but yet with fertilised ova; but I did not know whether it might not be case of parthogenesis or a strange accident of some floating spermatozoa;¹⁰ well yesterday I had an account by a man who watching some shells, saw one protrude its long probosciformed penis, & insert it in the shell of an adjoining individual!¹¹ So here is a load off my mind.—

You speak of species not having any material base to rest on; but is this any greater hardship than deciding what deserves to be called a variety & be designated by a greek letter. When I was at systematic work, I know I longed to have no other difficulty (great enough) than deciding whether the form was distinct enough to deserve a name; & not to be haunted with undefined & unanswerable question whether it was a true species.¹² What a jump it is from a well marked variety, produced by natural cause, to a species produced by the separate act of the Hand of God. But I am running on foolishly.— By the way I met the other day Phillips, the Palæontologist,¹³ & he asked me “how do you define a species?”— I answered “I cannot” Whereupon he said “at last I have found out the only true definition,—‘any form which has ever had a specific name”!

I am infinitely obliged to you for your offer (if you can ever find time, & how much overworked you seem to be) of considering again a list of close species, such as Hooker would perhaps lump together: you could not do me a more essential service.¹⁴

If you do it, will you please take, if in your power, large & small orders as they come, for possibly there may be some difference in the rule in large natural & small broken families. I intend to go into this with Ledebour, as far as mere varieties are concerned.¹⁵ In all Ledebour & many other Floras, I find the rule universal of the large genera presenting most varieties.¹⁶ In the British Flora, by M^r Watsons aid,¹⁷ I have struck out the most trifling varieties & I find the rule holds good, as it also does with the forms which most British Botanists rank as species, but which some one Botanist has considered a variety. This rule, as I must consider it of the large genera varying most, I look at as most important for my work & I believe it to be the foundation of the manner in which all beings are grouped in classes &c, together with what I rather vaguely call my principle of divergence ie the tendency to the preservation from extinction of the most different members of each group.—¹⁸ But I am amusing myself by scribbling away all my notions without any mercy.

Forgive me, & believe | My dear Gray | Yours heartily obliged | C. Darwin

How I wish I knew what large, (for large it must be) Moth or Humble Bee visits & fertilises Lobelia fulgens in its native home: do you know any southern young Botanist who w^d look to this? I would cover a plant with a very coarse gauze cap, & then not a pod would set I believe. But by Jove I have broken my vow by a sort of question or request!