LETTER 189. TO A.R. WALLACE. Down, January 22nd, 1866.

LETTER 189. TO A.R. WALLACE. Down, January 22nd, 1866.

I thank you for your paper on pigeons (189/1. "On the Pigeons of the Malay Archipelago" (The "Ibis," October, 1865). Mr. Wallace points out (page 366) that "the most striking superabundance of pigeons, as well as of parrots, is confined to the Australo-Malayan sub-region in which...the forest-haunting and fruit-eating mammals, such as monkeys and squirrels, are totally absent." He points out also that monkeys are "exceedingly destructive to eggs and young birds."), which interested me, as everything that you write does. Who would ever have dreamed that monkeys influenced the distribution of pigeons and parrots! But I have had a still higher satisfaction, for I finished your paper yesterday in the "Linnean Transactions." (189/2. "Linn. Soc. Trans." XXV.: a paper on the geographical distribution and variability of the Malayan Papilionidae.) It is admirably done. I cannot conceive that the most firm believer in species could read it without being staggered. Such papers will make many more converts among naturalists than long-winded books such as I shall write if I have strength. I have been particularly struck with your remarks on dimorphism; but I cannot quite understand one point (page 22), (189/3. The passage referred to in this letter as needing further explanation is the following: "The last six cases of mimicry are especially instructive, because they seem to indicate one of the processes by which dimorphic forms have been produced. When, as in these cases, one sex differs much from the other, and varies greatly itself, it may happen that individual variations will occasionally occur, having a distant resemblance to groups which are the objects of mimicry, and which it is therefore advantageous to resemble. Such a variety will have a better chance of preservation; the individuals possessing it will be multiplied; and their accidental likeness to the favoured group will be rendered permanent by hereditary transmission, and each successive variation which increases the resemblance being preserved, and all variations departing from the favoured type having less chance of preservation, there will in time result those singular cases of two or more isolated and fixed forms bound together by that intimate relationship which constitutes them the sexes of a single species. The reason why the females are more subject to this kind of modification than the males is, probably, that their slower flight, when laden with eggs, and their exposure to attack while in the act of depositing their eggs upon leaves, render it especially advantageous for them to have some additional protection. This they at once obtain by acquiring a resemblance to other species which, from whatever cause, enjoy a comparative immunity from persecution." Mr. Wallace has been good enough to give us the following note on the above passage: "The above quotation deals solely with the question of how certain females of the polymorphic species (Papilio Memnon, P. Pammon, and others) have been so modified as to mimic species of a quite distinct section of the genus; but it does not attempt to explain why or how the other very variable types of female arose, and this was Darwin's difficulty. As the letter I wrote in reply is lost, and as it is rather difficult to explain the matter clearly without reference to the coloured figures, I must go into some little detail, and give now what was probably the explanation I gave at the time. The male of Papilio Memnon is a large black butterfly with the nervures towards the margins of the wings bordered with bluish gray dots. It is a forest insect, and the very dark colour renders it conspicuous; but it is a strong flier, and thus survives. To the female, however, this conspicuous mass of colour would be dangerous, owing to her slower flight, and the necessity for continually resting while depositing her eggs on the leaves of the food-plant of the larva. She has accordingly acquired lighter and more varied tints. The marginal gray-dotted stripes of the male have become of a brownish ash and much wider on the fore wings, while the margin of the hind wings is yellowish, with a more defined spot near the anal angle. This is the form most nearly like the male, but it is comparatively rare, the more common being much lighter in colour, the bluish gray of the hind wings being often entirely replaced by a broad band of yellowish white. The anal angle is orange-yellow, and there is a bright red spot at the base of the fore wings. Between these two extremes there is every possible variation. Now, it is quite certain that this varying mixture of brown, black, white, yellow, and red is far less conspicuous amid the ever-changing hues of the forest with their glints of sunshine everywhere penetrating so as to form strong contrasts and patches of light and shade. Hence ALL the females--one at one time and one at another--get SOME protection, and that is sufficient to enable them to live long enough to lay their eggs, when their work is finished. Still, under bad conditions they only just managed to survive, and as the colouring of some of these varying females very much resembled that of the protected butterflies of the P. coon group (perhaps at a time when the tails of the latter were not fully developed) any rudiments of a prolongation of the wing into a tail added to the protective resemblance, and was therefore preserved. The woodcuts of some of these forms in my "Malay Archipelago" (i., page 200) will enable those who have this book at hand better to understand the foregoing explanation."), and should be grateful for an explanation, for I want fully to understand you. How can one female form be selected and the intermediate forms die out, without also the other extreme form also dying out from not having the advantages of the first selected form? for, as I understand, both female forms occur on the same island. I quite agree with your distinction between dimorphic forms and varieties; but I doubt whether your criterion of dimorphic forms not producing intermediate offspring will suffice, for I know of a good many varieties which must be so called that will not blend or intermix, but produce offspring quite like either parent.

I have been particularly struck with your remarks on geographical distribution in Celebes. It is impossible that anything could be better put, and would give a cold shudder to the immutable naturalists.

And now I am going to ask a question which you will not like. How does your journal get on? It will be a shame if you do not popularise your researches.

LETTER 190. A.R. WALLACE TO CHARLES DARWIN. Hurstpierpoint, Sussex, July 2nd, 1866.

I have been so repeatedly struck by the utter inability of numbers of intelligent persons to see clearly, or at all, the self-acting and necessary effects of Natural Selection, that I am led to conclude that the term itself, and your mode of illustrating it, however clear and beautiful to many of us, are yet not the best adapted to impress it on the general naturalist public. The two last cases of the misunderstanding are: (1) the article on "Darwin and his Teachings" in the last "Quarterly Journal of Science," which, though very well written and on the whole appreciative, yet concludes with a charge of something like blindness, in your not seeing that Natural Selection requires the constant watching of an intelligent "chooser," like man's selection to which you so often compare it; and (2) in Janet's recent work on the "Materialism of the Present Day," reviewed in last Saturday's "Reader," by an extract from which I see that he considers your weak point to be that you do not see that "thought and direction are essential to the action of Natural Selection." The same objection has been made a score of times by your chief opponents, and I have heard it as often stated myself in conversation. Now, I think this arises almost entirely from your choice of the term "Natural Selection" and so constantly comparing it in its effects to Man's Selection, and also your so frequently personifying nature as "selecting," as "preferring," as "seeking only the good of the species," etc., etc. To the few this is as clear as daylight, and beautifully suggestive, but to many it is evidently a stumbling-block. I wish, therefore, to suggest to you the possibility of entirely avoiding this source of misconception in your great work (if not now too late), and also in any future editions of the "Origin," and I think it may be done without difficulty and very effectually by adopting Spencer's term (which he generally uses in preference to Natural Selection)--viz., "survival of the fittest."

This term is the plain expression of the fact; Natural Selection is a metaphorical expression of it, and to a certain degree indirect and incorrect, since, even personifying Nature, she does not so much select special variations as exterminate the most unfavourable ones.

Combined with the enormous multiplying powers of all organisms, and the "struggle for existence" leading to the constant destruction of by far the largest proportion--facts which no one of your opponents, as far as I am aware, has denied or misunderstood--"the survival of the fittest" rather than of those who were less fit could not possibly be denied or misunderstood. Neither would it be possible to say that to ensure the "survival of the fittest" any intelligent chooser was necessary; whereas when you say Natural Selection acts so as to choose those that are fittest, it IS misunderstood, and apparently always will be. Referring to your book, I find such expressions as "Man selects only for his own good; Nature only for that of the being which she tends." This, it seems, will always be misunderstood; but if you had said "Man selects only for his own good; Nature, by the inevitable 'survival of the fittest,' only for that of the being she tends," it would have been less liable to be so.

I find you use the term "Natural Selection" in two senses: (1) for the simple preservation of favourable and rejection of unfavourable variations, in which case it is equivalent to "survival of the fittest"; and (2) for the effect or change produced by this preservation, as when you say, "To sum up the circumstances favourable or unfavourable to Natural Selection," and again, "Isolation, also, is an important element in the process of Natural Selection." Here it is not merely "survival of the fittest," but change produced by survival of the fittest, that is meant. On looking over your fourth chapter, I find that these alterations of terms can be in most cases easily made, while in some cases the addition of "or survival of the fittest" after "Natural Selection" would be best; and in others, less likely to be misunderstood, the original term may stand alone.

I could not venture to propose to any other person so great an alteration of terms, but you, I am sure, will give it an impartial consideration, and if you really think the change will produce a better understanding of your work, will not hesitate to adopt it.

It is evidently also necessary not to personify "Nature" too much--though I am very apt to do it myself--since people will not understand that all such phrases are metaphors. Natural Selection is, when understood, so necessary and self-evident a principle, that it is a pity it should be in any way obscured; and it therefore seems to me that the free use of "survival of the fittest," which is a compact and accurate definition of it, would tend much to its being more widely accepted, and prevent it being so much misrepresented and misunderstood.

There is another objection made by Janet which is also a very common one. It is that the chances are almost infinite against the particular kind of variation required being coincident with each change of external conditions, to enable an animal to become modified by Natural Selection in harmony with such changed conditions; especially when we consider that, to have produced the almost infinite modifications of organic beings, this coincidence must have taken place an almost infinite number of times.

Now, it seems to me that you have yourself led to this objection being made, by so often stating the case too strongly against yourself. For example, at the commencement of Chapter IV. you ask if it is "improbable that useful variations should sometimes occur in the course of thousands of generations"; and a little further on you say, "unless profitable variations do occur, Natural Selection can do nothing." Now, such expressions have given your opponents the advantage of assuming that favourable variations are rare accidents, or may even for long periods never occur at all, and thus Janet's argument would appear to many to have great force. I think it would be better to do away with all such qualifying expressions, and constantly maintain (what I certainly believe to be the fact) that variations of every kind are always occurring in every part of every species, and therefore that favourable variations are always ready when wanted. You have, I am sure, abundant materials to prove this; and it is, I believe, the grand fact that renders modification and adaptation to conditions almost always possible. I would put the burthen of proof on my opponents to show that any one organ, structure, or faculty does not vary, even during one generation, among all the individuals of a species; and also to show any mode or way in which any such organ, etc., does not vary. I would ask them to give any reason for supposing that any organ, etc., is ever absolutely identical at any one time in all the individuals of a species, and if not then it is always varying, and there are always materials which, from the simple fact that "the fittest survive," will tend to the modification of the race into harmony with changed conditions.

I hope these remarks may be intelligible to you, and that you will be so kind as to let me know what you think of them.

I have not heard for some time how you are getting on. I hope you are still improving in health, and that you will now be able to get on with your great work, for which so many thousands are looking with interest.