In the interesting preface to the reprint of the famous paper On the Tendencies of Varieties to depart Indefinitely from the Original Type, Mr. Wallace recites the several researches which he made in quest of that "form" till, when lying ill with fever at Ternate, in February, 1858, something led him to think of the "positive checks" described by Malthus in his Essay on Population, a book which he had read some years before. Oddly enough, therefore, the honours lie with the maligned Haileybury Reverend Professor of Political Economy in furnishing both Darwin and Wallace with the clue. The "positive checks"--war, disease, famine--Wallace felt must act even more effectively on the lower animals than on man, because of their more rapid rate of multiplication. And he tells us, in the prefatory note to a reprint of his paper, "there suddenly flashed on me the _idea_ of the survival of the fittest, and in the two hours that elapsed before my ague fit was over I had thought out the whole of the theory, and in the two succeeding evenings wrote it out in full and sent it by the next post to Mr. Darwin," asking him, if he thought well of the essay, to send it to Lyell. This Darwin did with the following remarks: "Your words have come true with a vengeance--that I should be forestalled.... I never saw a more striking coincidence; if Wallace had my MS. sketch written out in 1842, he could not have made a better short abstract! Even his terms now stand as heads of my chapters. Please return me the MS., which he does not say he wishes me to publish; but I shall, of course, at once write and offer to send to any journal. So all my originality, whatever it may amount to, will be smashed, though my book, if it will ever have any value, will not be deteriorated, as all the labour consists in the application of the theory." Darwin came out well in this business. For to have hit upon a theory which interprets so large a question as the origin and causes of modification of life-forms; to keep on turning it over and over again in the mind for twenty long years; to spend the working hours of every day in collection and verification of facts for and against it; and then to have another man launching a "bolt from the blue" in the shape of a paper with exactly the same theory, might well disturb even a philosopher of Darwin's serenity.