INTRODUCTORY NOTE TO CHAPTER II IN PRESENT EDITION 
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 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° 
F., 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 on man. Then I thought of the enormously rapid multi- 
plication of animals, causing these checks to be much more 
effective in them than in the case of man; and while ponder- 
ing 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 inferior to those that 
survived. In the two hours that elapsed before my ague fit 
was over I had thought out almost the whole of the theory, 
and the same evening I sketched the draft of my paper, and 
in the two succeeding evenings wrote it out in full, and sent 
it by the next post to Mr. Darwin. Up to this time the only 
letters I had received from him were those printed in the 
second volume of his Life and Letters, (vol. ii. pp. 95 and 108), 
