428 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 
Fic. 120.—ALFRED RussEL WALLACE, BORN 1823. 
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 sud- 
denly flashed upon me the idca of the survival of the fittest-— 
that the individuals removed by these checks must be on the 
