“I hope it is a satisfaction to you to reflect--and very few things in my life have been more satisfactory to me--that we have never felt any jealousy towards each other, though in one sense rivals. I believe that I can say this of myself with truth, and I am absolutely sure that it is true of you.” CHAPTER XII. THE GROWTH OF WALLACE’S CONVICTIONS ON EVOLUTION AND DISCOVERY OF NATURAL SELECTION--BORNEO 1855--TERNATE 1858. We have already seen in the earlier part of this volume, the gradual development of the theory of Natural Selection in the mind of Darwin, and the long succession of experiments and observations which he undertook before he could bring himself to publish anything upon the subject, as well as the conditions which forced him to a hurried publication in the end. It is of the deepest interest to compare with this the account which Wallace has given us of the mental process by which he arrived at the same conclusions. This deeply interesting personal history has only been known during the last few years; in 1891 Wallace republished his “Essays on Natural Selection” in one volume, combined with “Tropical Nature,” and he has added (on pp. 20, 21) the following introductory note to Chapter II., viz. the reprint of his Linnean Society Memoir “On the Tendencies of Varieties to depart indefinitely from the Original Type.” The note is here reprinted in full:-- “As this chapter sets forth the main features of a theory identical with that discovered by Mr. Darwin many years before but not then published, and as it has thus an historical interest, a few words of personal statement may be permissible. After writing the preceding paper [“On the Law which has Regulated the Introduction of New Species”] the question of _how_ changes of species could have been brought about was rarely out of my mind, but no satisfactory conclusion was reached till February 1858. At that time I was suffering from a rather severe attack of intermittent fever at Ternate in the Moluccas, and one day, while lying on my bed during the cold fit, wrapped in blankets, though the thermometer was at 88° Fahr., the problem again presented itself to me, and something led me to think of the ‘positive checks’ described by Malthus in his ‘Essay on Population,’ a work I had read several years before, and which had made a deep and permanent impression on my mind. These checks--war, disease, famine and the like--must, it occurred to me, act on animals as well as man. Then I thought of the enormously rapid multiplication of animals, causing these checks to be much more effective in them than in the case of man; and while pondering vaguely on this fact there suddenly flashed upon me the _idea_ of the survival of the fittest--that the individuals removed by these checks must be on the whole