To Asa Gray 20 July 1
Down Bromley Kent
My dear Dr Gray
What you say about extinction, in regard to small genera & local disjunction, being hypothetical seems very just.2 Something direct, however, could be advanced on this head from fossil shells; but hypothetical such notions must remain. It is not a little egotistical, but I shd. like to tell you, (& I do not think I have) how I view my work. Nineteen years (!) ago it occurred to me that whilst otherwise employed on Nat. Hist, I might perhaps do good if I noted any sort of facts bearing on the question of the origin of species; & this I have since been doing. Either species have been independently created, or they have descended from other species, like varieties from one species. I think it can be shown to be probable that man gets his most distinct varieties by preserving such as arise best worth keeping & destroying the others,—but I shd. fill a quire if I were to go on. To be brief I assume that species arise like our domestic varieties with much extinction; & then test this hypothesis by comparison with as many general & pretty well established propositions as I can find made out,—in geograph. distribution, geological history—affinities &c &c &c.. And it seems to me, that supposing that such hypothesis were to explain general propositions, we ought, in accordance with common way of following all sciences, to admit it, till some better hypothesis be found out. For to my mind to say that species were created so & so is no scientific explanation only a reverent way of saying it is so & so. But it is nonsensical trying to show how I try to proceed in compass of a note. But as an honest man I must tell you that I have come to the heteredox conclusion that there are no such things as independently created species—that species are only strongly defined varieties. I know that this will make you despise me.— I do not much underrate the many huge difficulties on this view, but yet it seems to me to explain too much, otherwise inexplicable, to be false. Just to allude to one point in your last note, viz about species of the same genus generally having a common or continuous area; if they are actual lineal descendants of one species, this of course would be the case; & the sadly too many exceptions (for me) have to be explained by climatal & geological changes. A fortiori on this view (but on exactly same grounds) all the individuals of the same species shd. have a continuous distribution. On this latter branch of the subject I have put a chapter together, & Hooker kindly read it over:3 I thought the exceptions & difficulties were so great that on the whole the balance weighed against my notions, but I was much pleased to find that it seemed to have considerable weight with Hooker, who said he had never been so much staggered about the permanence of species.—4
I must say one word more in justification (for I feel sure that your tendency will be to despise me & my crotchets) that all my notion about how species change are derived from long-continued study of the works of (& converse with) agriculturists & horticulturists; & I believe I see my way pretty clearly on the means used by nature to change her species & adapt them to the wondrous & exquisitely beautiful contingencies to which every living being is exposed.
Thank you much for what you say about possibility of crossing of the grasses: I have been often astounded at what Botanists say on fertilisation in the bud: I have seen Cruciferæ mentioned as instance, which every gardener knows how difficult it is to protect from crossing!
What you say on Papilionaceous flowers is very true; & I have no facts to show that varieties are crossed; but yet (& the same remark is applicable in a beautiful way to Fumaria & Diclytra as I noticed many years ago) I must believe that the flowers are constructed partly in direct relation to the visits of insects; & how insects can avoid bringing pollen from other individuals I cannot understand.5 It is really pretty to watch the action of a Humble -Bee on the scarlet Kidney Bean, & in this genus (& in Lathyrus grandifloris) the honey is so placed that the Bee invariably alight on that one side of the flower towards which the spiral pistil is protruded (bringing out with it pollen) & by the depression of the wing-petal is forced against the Bee’s side all dusted with pollen. N.B if you will look at bed of scarlet Kidney Bean you will find that the wing-petals on the left-side alone are all scratched by the tarsi of the Bees.6 In the Broom the pistil is rubbed on centre of back of Bee &c. &c.— I suspect there is something to be made out about the Leguminosæ which will bring the case within our theory;7 though I have failed to do so.
Our theory will explain why in vegetable & animal kingdom the act of fertilisation even in hermaphrodites usually takes place sub-jove, though thus exposed to the great injury from damp & rain.8 In animals in which the semen cannot, like pollen, be occasionally carried by insects or wind; there is no case of land-animals being hermaphrodite without the concourse of two individuals.
But my letter has been horribly egotistical: but your letters always so greatly interest me; & what is more they have in simple truth been of the utmost value to me.
Your’s most sincerely & gratefully | C. Darwin
Believes species have arisen, like domestic varieties, with much extinction, and that there are no such things as independently created species. Explains why he believes species of the same genus generally have a common or continuous area; they are actual lineal descendants.
Discusses fertilisation in the bud and the insect pollination of papilionaceous flowers. His theory explains why, despite the risk of injury, cross-fertilisation is usual in the animal and vegetable kingdoms, even in hermaphrodites.