WCP4424

[1]

Broadstone, Dorset.

Februar^y.. 28^th. 1904

Prof. E. B. Poulton

My dear Poulton

I received your "Address" yesterday, & yesterday evening I read it through with great interest & pleasure; and this morning I will give you the few critical remarks that occur to me.

The main part of it is a most excellent account of the subject of "species" and viewed at various epochs. The chief thing that strikes me here, is, how true was Darwin’s remark that evolutionary ideas would make practically no difference in of our descriptions of them ^species, & in our viewing them as real entities, but only in our mode of regarding them fundamentally. Even among [2] Darwinians we still have "lumpers" and "splitters", and individual problems of species, sub-species, races, varieties &c remain much as they were.

I was much interested in several of your quotations from "More Letters" for, since I received them I have been so much occupied with other work & other subjects, that I have not yet found time to read them.

Curiously, I have just been reading Max Müllers "Old Lang Syne" & noticed how little he understood Darwin’s work, and how weak was his argument from "language" with which he thought he had quite floored poor Darwin, when he listened to him so patiently, & did not reply!

Now for the great problems of self-fertil[isatio]n[,] hybridity &c.

1. As to Heterostyled plants, I cannot believe, as you seem to argue, that while the great fertility of legitimate crosses has been produced through selection, the infertility of the illegitimate crosses has been merely [3] an incidental result of their isolation. We must look to the beginning of this strange set of adaptations, when the functions of all the ♂ & ♀ organs in each flower were alike. We must suppose some variation in amount of fertility of the crosses effected through particular anthers & stigmas, and all variations tending to increase this divergence, and to limit it to the proper variations in lengths of stamens & pis[t]ils, would have been selected, and during this process, any extra sterility of the one cross w[oul]d have been as important as an extra degree of fertility of the other cross.

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2. Your remark at top of p.47[?], seems to me quite untenable. For if, at the beginning, there were no "injurious results" in self-fertilisation, why did special adaptations for x fert[ilisatio]n ever arise? There could have been no motive-power — no sufficient reason, except danger to the species by deficient fertility, or unadaptability

3. If the infertility of illegit[imate] crosses in Heterostyled plants were an incidental [4]¹ result, it should not be rigid; that is, in some such plants we should find all degrees of fertility in illegitimate crosses. I do not know whether this has ever been found.

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4. Though I quite agree with you that time may be essential to the production of infertility between marked varieties, & that Huxley’s argument is therefore invalid; there are also two other points to be considered.

(a) In a very minute fraction of known species is there any proof that even the closest species (yet quite distinct) are always infertile when crossed. The cases I have adduced at pp.159-163 of my Darwinism, renders it probable that there is no such general law.

(b) But I cannot believe that time alone would incidentally lead to sterility, without perfect isolation and for enormous period. Wherever there has not been such isolation selection must have acted during the initial stages to prevent swamping by intercrossing. I consider Darwin’s belief that selection [5]² could not act to produce infertility between incipient species, of no value because it appears to have been founded wholly on the opinion of Geo. Darwin that it was not mathematically possible. But I feel sure that the opinion of a mathematician who has not carefully taken account of all the biological conditions is valueless. And two mathematical friends (one interested in biology) have assured me that my mathematical argument at p.181-2 of my Darwinism, is sound, while neither Darwins G. Darwin nor any one else has proved its fallacy. But I admit it is not rigid & would act only under certain (probable) conditions & then but slowly — Given ample time it would produce ample effect. It is in fact a vera causa, & if so gets over the difficulty.

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4. [sic] I think the cases quoted by me (above referred to ^{Darwinism p.160,}) do prove that there is a physiological evil result in close interbreeding without selection, — but that with continual [6] natural selection, (as there is always usually is [sic] in nature) there is no evil result whatever. But, when from any adverse conditions, a species is hard pressed, diminishes in numbers, and because restricted to a narrow area, there is not sufficient scope for natural selection to act, and any variations tending to facilitate crosses of the more unrelated and unlike individuals becomes important. On reading through again my discussion of the cases of self-fertilised plants which you refer to, it seems to me that it renders the whole subject tolerably intelligible, — but you refer to pp.321-26 — whereas the following pages on to p.332 — are even more important as showing how the principle suggested actually works in nature.

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5. My conclusion on the whole subject is, that the most probable original cause of differentiation of sex, is (as Weismann I think maintains) the constant production [7] of sufficient variability essential for evolution to work with; and, that the benefits of cross-fertilisation are fundamentally the same — the production of those constant and ample variations by which each species is — in the first place kept up to the highest standard of life-maintenance, and in the second is always ready to become modified in accordance with modified conditions.

This great principle really is at the root of all these problems, & explains all the wonderful diversity in nature. It shows which why plants — individually fixed to one spot — have either enormous powers of seed-disposal, or extraordinary arrangements for cross-fertilisation, both tending to increase variability up to the full degree that is required.

And I think it also explains that most wonderful phenomenon of insect-transformations from the vermiform, almost stationary, type, to the highly mobile winged creatures that have become the most dominant of living things! Has it [8]³ ever been suggested ^before, that the development of winged insects is the exact correlative of the complex structure of orchids, and labiates, and peas, — of downy and winged and hooked, and dust-like seeds — all alike for the purpose of diffusing the individual in all directions, crossing them with each other in every possible degree, & thus keeping up the fundamental essential for evolution — variability!

In an old Scrap-book I have come across a photo[graph] of a pupa & leaf sent me by Darwin with a holograph letter⁴. I cut it out & send it to you, as you no doubt have books of such things. It wants clearing of gum & remounting.

Fred Birch was delighted with your kindness to him in every way. To avoid the wet season in Guiana he is going first to Trinidad, where Mr Kaye told is [sic] there is fine collecting country. As Trinidad is a centre of trade for the Orinooko[sic], I recommended him to make all enquiries about that almost unknown region, for future use.

Yours very truly| Alfred R. Wallace [signature]