Discusses Natural Selection.
A typical letter in English and signed by author.
Missing words at the start of the second paragraph.
An original MS
Pages with text: 5
Typewritten with handwritten annotations.
Transcriber: Lord, Annette
Transcription date: July 27, 2012
Scrutiny: 15/01/2013 - Catchpole, Caroline;
Signed off: no
Monadnock, New Hamp[shire]
July 22, 1905
My dear Dr Wallace, --
All winter I have been thinking a great many things to you, all the more as I have during these months been very much with you, by reading (strange to say, for the first time) your delightful Malay Archipelago, and much of your writings on protective coloration. I was positively lonesome at having to part from you at the end.
[wording covered up], it is the laws of optics to which the visible parts of animals must defer if they are to serve those animals in the life struggle, and as you have yourself pointed out, the parallel development of hunter and hunted, makes the success of each sure to hang, in ever so many encounters, upon very small differences, and differences in mutual visibility quite as much as in any other thing.
Let a man stand among swarming insects where their background, all about him has the usual jungle-diversity, and try to catch one of them with his hand. He will soon discover that he instinctively tries for the most visible one. Hundreds of them are visible, but amidst all his difficulties, he will be forced to seek the most visible at the moment of seizing. Just at this moment the color-coalition of one of these insects with his background, or even that of a part of him, will decide his fate and save him. My point is that just at the last moment the question is of visibility. I am well aware [] [2 at top of page] that you heartily agree to all this.
A skunk may get very near his small prey by scent, but doubtless he would seldom catch it the more alert kinds if he were blind. [Word crossed out and overwritten] They would always jump away at the last moment. There is such a difference between almost catching and catching! For these reasons it is precisely the circumstances which attend this last moment that are most worth studying for explanations of animals’ colors and patterns.
To save my eyes, I am taking the liberty of sending you a letter I wrote C Hart Merriam about the skunks. If you will kindly take the trouble to let me know that you expect to be at Parkstone, I wish also to send you a winter landscape made wholly of the feathers of a blue jay, or rather of the skin, i.e. patches of it re-arranged, to show that winter being theis birds’ exposed time, amidst our deciduous tree-landscape, bare of leaves, he is a winter picture of wonderful perfection. In this picture every detail of the jay’s surface, and every (which means, as well, of course, every pattern,) appears in full operation.
I have done somewhat the same with the colors of a bird of paradise, to show the same thing, that all brilliant birds are precisely related to their habitant [sic] as the enclosed wall-paper bird is to the wall-paper he fits in and that there is no such thing, save in a cabinet, as a conspicuous bird. This too (the bird of Paradise sketch) I will send you, if you please, after I have shown everything to the A.O.U, in Nov[ember].
This wall-paper bird, or any so-called conspicuous bird is, even without regard to his background, less conspicuous than if he were monochrome, being cut into separate entities, and when he gets into the place you cut him out of, he is gone!
All this has been fragmentarily observed by many naturalists, but strange to say, never perceived as the universal truth. This bird of paradise sketch is made wholly of the colors of the bird and is approximately true to Nature, but in the forest, as you and I know, there is a super-added bath of green light. For this reason, this scene, bird and all, should be seen through moderately green glass.
The green glass will convert the yellow light places and the similar bird of P[aradise] plumes to a representation of the brightest places in the higher foliage. I feel that [] [3 at top of page] you will agree, that a function so absolute as this effacing of the fronts of skunks’ and badgers’ looming forms, (see photo’s [sic]) as they approach their prey on the surface of the ground (especially in view of the fact that hunting by scent makes them need time, ) and the corresponding effacing of the rears of the fleeing animals, deer, hares, antelopes etc. just when the cougar, or the smaller enemy, would make one last spring; a function so plainly coming at the most critical point in each animal’s life, is therefore proved to be the function. Of course, any organ or organization has all the uses that Nature can make of it, but there are still the pivotal ones. These photographs show the famous deer-buttocks and skunk-top-white to be, among the most perfect of all the multitudes of devices, all accomplishing the one end: viz., that the spectator seems to see through the wearer to the background, so that there appears to be only a space, where there is, really, an animal. These white card photo’s [sic] show clearly that it is useless to discuss the function of any animal patterns without full knowledge as to the direction at which they are beheld when in operation, since to look at them, near, from a point one inch lower than they, brings them against the sky, and one inch higher, against the earth. So that even among small forest birds, the habit of getting food mainly from over-head, as perhaps one of our vireos does, could make him need a totally different coloration from that required by a neighbor in the same tree who picked things most often from beneath him.
I feel that my photos show that no considerations less exact than these have any bearing on such questions. This skunk and deer business throws new light on gull’s white heads, etc. They fear little from predatory birds, etc. and when seen against the sky, these white heads, like the skunk’s, are the least conspicuous, and in fact, often invisible, by the shrimp, etc. which they pluck from the shallows and which would dodge away, if possible.
All the revelation of actual concealment-functions of so-[] [4 at top of page] called conspicuous patterns, removes more and more of the ground for the hypothesis of mimicry, in such things as butterflies and snakes.
The pattern of a South American Batesian Mimic Butterfly is the most perfect I can conceive for oftenest effacing the insect, as it moves about in the alternating sunlight and shadow with ever varying backgrounds, so that now it is its black that doesn’t show, now its yellow, etc. Our Copperhead snake is an absolutely marvellous picture, every color note perfect past all human power to imitate, of dead leaves. On any rotund forms, [t]his is only possible, of course, by means of the counter-gradation of shadowing. What is it to mimic a device that so magically conceals, annihilates the wearer, what but to shaowre the benefits of the device! Yet, I could show that every snake or butterfly mimicked, is just as perfectly effaced by its color in his habitat, as the Copperhead or this wall-paper bird.
Of course, I need not say to you that Nature has to make, as it were, composite photographs of these animals’ backgrounds true only to their average, but in this way they become truth itself, -- actual art! And, in fact, is it not very true that people have so far too much rested this protective coloration question on whether it is possible to find or see the protected individual? The case is quite other. Nature is one great heaving, surging, mass of life, wherein each predator, as his hunger mounts up to the point for over-coming his inertia, looks about him for the easiest means of dining, and [word crossed out and overwritten] three of the factors in his resultant action are the relative edibility, and relative catchability, and the relative alluringness as to simple conspicuousness, of the various animals he sees about him.
William Brewster says it is useless to try to keep white pigeons among his flock at Concord, Mass. Hawks weed them out. Now a pigeon is not child’s play for a hawk to catch, and the white just as surely condemns the wearer to greater danger, because he can be more un- [] [5 at top of page] erringly struck at in the air, precisely as one finds, in catching a white insect among dim ones. The case is on a different basis, the question being simply, what coloration grants a species the greatest number of escapes from conspicuousness or the greatest number of occasions when one of its individuals escapes detection altogether.
Hence, in those cvast tropical forests a sufficiently successful effacer can help a species to so thrive as to flood the whole region and furnish hordes of individuals to be constantly in full sight, over-flowed out of their protective habitat. If this is even the case, the birds of the region might, (iIs it not so?) having become accustomed to fail to secure these insects when they were dodging about in and out of the thick shelter of leaves and of sunlight and shadow, have come to regard them as not part of their food, and seldom touch them. I noticed in Trinidad that fly catching birds seldom attempted to catch anything swift.
I trust that I don’t presume too much in offering you so long a letter.
1. This is a letter from Abbott H Thayer.
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