140 THE WONDERFUL CENTURY. CHAP. xm. 



fits, while again considering the problem of the origin 

 of species, something led me to think of Malthus' Essay 

 on Population (which I had read about ten years before), 

 and the " positive checks " war, disease, famine, acci- 

 dents, etc. which he adduced as keeping all savage 

 populations nearly stationary. It then occurred to me 

 that these checks must also act upon animals, and keep 

 down their numbers; and as they increase so much faster 

 than man does, while their numbers are always very 

 nearly or quite stationary, it was clear that these checks 

 in their case must be far more powerful, since a number 

 equal to the whole increase must be cut off by them 

 every year. While vaguely thinking how this would 

 affect any species, 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. Then, considering the varia- 

 tions continually occurring in every fresh generation of 

 animals or plants, and the changes of climate, of food, of 

 enemies always in progress, the whole method of specific 

 modification became clear to me, and in the two hours of 

 my fit I had thought out the main points of the theory. 

 That same evening I sketched out the draft of a paper; 

 in the two succeeding evenings I wrote it out, and sent 

 it by the next post to Mr. Darwin. 1 I fully expected it 

 would be as new to him as it was to myself, because he 

 had informed me by letter that he was engaged on a 

 work intended to show in what way species and varie- 

 ties differ from each other, adding, " my work will not 

 fix or settle anything." I was therefore surprised to 

 find that he had really arrived at the very same theory 

 1 These two papers are reprinted in my " Natural Selection and 

 Tropical Nature." 



