43 6 BIOLOGY AND ITS MAKERS 



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 



Fig. i 20. — Alfred Russel Wallace, 1823-1913. 



sse 

 of 



the enormously rapid multiplication of animals, causing the 

 checks to be much more effective in them than in the case 

 man; and while pondering vaguely on this fact, there sud- 

 denly flashed upon me the idea of the survival of the fittest — 

 that the individuals removed by these checks must be on the 



