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description, and if neither Darwin nor myself had hit upon “Natural Selection," I might have spent the best years of my life in this comparatively profitless work. But the new ideas swept all this away. I have for the most part left others to describe my discoveries, and have devoted myself to the great generalizations which the laborious work of speciesdescribers had rendered possible. In this letter to Bates I enclosed a memorandum of my estimate of the number of distinct species of insects I had collected up to the time of writing—three years and a half, nearly one year of which had been lost in journeys, illnesses, and various delays. The totals were as follows :

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It was while waiting at Ternate in order to get ready for my next journey, and to decide where I should go, that the idea already referred to occurred to me. It has been shown how, for the preceding eight or nine years, the great problem of the origin of species had been continually pondered over, and how my varied observations and study had been made use of to lay the foundation for its full discussion and elucidation. My paper written at Sarawak rendered it certain to my mind that the change had taken place by natural succession and descent-one species becoming changed either slowly or rapidly into another. But the exact process of the change and the causes which led to it were absolutely unknown and appeared almost inconceivable. The great difficulty was to understand how, if one species was gradually changed into another, there continued to be so many quite distinct species, so many which differed from their nearest

allies by slight yet perfectly definite and constant characters. One would expect that if it was a law of nature that species were continually changing so as to become in time new and distinct species, the world would be full of an inextricable mixture of various slightly different forms, so that the well-defined and constant species we see would not exist. Again, not only are species, as a rule, separated from each other by distinct external characters, but they almost always differ also to some degree in their food, in the places they frequent, in their habits and instincts, and all these characters are quite as definite and constant as are the external characters. The problem then was, not only how and why do species change, but how and why do they change into new and welldefined species, distinguished from each other in so many ways; why and how do they become so exactly adapted to distinct modes of life; and why do all the intermediate grades die out (as geology shows they have died out) and leave only clearly defined and well-marked species, genera, and higher groups of animals.

Now, the new idea or principle which Darwin had arrived at twenty years before, and which occurred to me at this time, answers all these questions and solves all these difficulties, and it is because it does so, and also because it is in itself self-evident and absolutely certain, that it has been accepted by the whole scientific world as affording a true solution of the great problem of the origin of species.

At the time in question I was suffering from a sharp attack of intermittent fever, and every day during the cold and succeeding hot fits had to lie down for several hours, during which time I had nothing to do but to think over any subjects then particularly interesting me. One day something brought to my recollection Malthus's “Principles of Population," which I had read about twelve years before. I thought of his clear exposition of “the positive checks to increase ”— disease, accidents, war, and famine—which keep down the population of savage races to so much lower an average than that of more civilized peoples. It then occurred to me that these causes or their equivalents are continually acting in the

case of animals also ; and as animals usually breed much more rapidly than does mankind, the destruction every year from these causes must be enormous in order to keep down the numbers of each species, since they evidently do not increase regularly from year to year, as otherwise the world would long ago have been densely crowded with those that breed most quickly. Vaguely thinking over the enormous and constant destruction which this implied, it occurred to me to ask the question, Why do some die and some live? And the answer was clearly, that on the whole the best fitted live. From the effects of disease the most healthy escaped ; from enemies, the strongest, the swiftest, or the most cunning ; from famine, the best hunters or those with the best digestion ; and so on. Then it suddenly flashed upon me that this self-acting process would necessarily improve the race, because in every generation the inferior would inevitably be killed off and the superior would remain—that is, the fittest would survive. Then at once I seemed to see the whole effect of this, that when changes of land and sea, or of climate, or of foodsupply, or of enemies occurred—and we know that such changes have always been taking place—and considering the amount of individual variation that my experience as a collector had shown me to exist, then it followed that all the changes necessary for the adaptation of the species to the changing conditions would be brought about; and as great changes in the environment are always slow, there would be ample time for the change to be effected by the survival of the best fitted in every generation. In this way every part of an animal's organization could be modified exactly as required, and in the very process of this modification the unmodified would die out, and thus the definite characters and the clear isolation of each new species would be explained. The more I thought over it the more I became convinced that I had at length found the long-soughtfor law of nature that solved the problem of the origin of species. For the next hour I thought over the deficiencies in the theories of Lamarck and of the author of the “ Vestiges," and I saw that my new theory supplemented these views and obviated every important difficulty. I waited anxiously for the termination of my fit so that I might at once make notes for a paper on the subject. The same evening I did this pretty fully, and on the two succeeding evenings wrote it out carefully in order to send it to Darwin by the next post, which would leave in a day or two.

I wrote a letter to him in which I said that I hoped the idea would be as new to him as it was to me, and that it would supply the missing factor to explain the origin of species. I asked him if he thought it sufficiently important to show it to Sir Charles Lyell, who had thought so highly of my former paper.

The subsequent history of this article is fully given in the “Life and Letters," volume ii., and I was, of course, very much surprised to find that the same idea had occurred to Darwin, and that he had already nearly completed a large work fully developing it. The paper is reprinted in my “Natural Selection and Tropical Nature," and in reading it now it must be remembered that it was but a hasty first sketch, that I had no opportunity of revising it before it was printed in the journal of the Linnean Society, and, especially, that at that time nobody had any idea of the constant variability of every common species, in every part and organ, which has since been proved to exist. Almost all the popular objections to Natural Selections are due to ignorance of this fact, and to the erroneous assumption that what are called " favourable variations” occur only rarely, instead of being abundant, as they certainly are, in every generation, and quite large enough for the efficient action of “survival of the fittest" in the improvement of the race.

During the first months of my residence at Ternate I made two visits to different parts of the large island of Gilolo, where my hunters obtained a number of very fine birds, but owing to the absence of good virgin forest and my own illhealth, I obtained very few insects. At length, on March 25, I obtained a passage to Dorey Harbour, on the north coast of New Guinea, in a trading schooner, which left me there, and called for me three or four months later to bring me back to Ternate. I was the first European who had lived alone on this great island; but partly owing to an accident which confined me to the house for a month, and partly because the locality was not a good one, I did not get the rare species of birds of paradise I had expected. I obtained, however, a number of new and rare birds and a fine collection of insects, though not so many of the larger and finer kinds as I expected. The weather had been unusually wet, and the place was unhealthy. I had four Malay servants with me, three of whom had fever as well as myself, and one of my hunters died, and though I should have liked to have stayed longer, we were all weak or unwell, and were very glad when the schooner arrived and took us back to Ternate, Here wholesome food and a comfortable house soon restored us to good health.

When I unpacked and examined my collections I found that the birds I had obtained were very numerous and beautiful, and as my journey and residence in New Guinea had created much interest among my numerous Dutch friends in Ternate, I determined to make a little exhibition of them. I accordingly let it be known that I would be glad to see visitors on the next Sunday afternoon. I had a long table in the verandah which I had covered with new “trade" calico, and on this I laid out the best specimens of all my most showy or strange birds. There were numbers of gorgeous lories, parrots, and parrakeets, white and black cockatoos, exquisite fruit-pigeons of a great variety of colours, many fine kingfishers from the largest to the most minute, as well as the beautiful raquet-tailed species, beautiful black, green, and blue ground-thrushes, some splendid specimens of the Papuan and King paradise-birds, and many beautiful bee-eaters, rollers, fly-catchers, grakles, sun-birds, and paradise-crows, making altogether such an assemblage of strange forms and brilliant colours as no one of my visitors had ever imagined to exist so near them. Even I myself was surprised at the beauty of the show when thus brought together and displayed on the white table, which so well set off their varied and brilliant colours.

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