46 
lations of what would happen if the principle were 
carried out without any let or hindrance. 
“A single cod-fish has been known to lay six million eggs within 
a year. If these eggs were all to become adult cod-fishes, and the 
multiplication were to continue at this rate for three or four years, 
the ocean would not afford room for the species.”—(Fiske. Outlines 
of Cosmic Philosophy, vol. z'z'., pp. 11-12.) 
With respect to the aphis—the “green blight” of the 
gardeners, with which most of us are more or less 
familiar, Mr. Theodore Wood says that a second genera 
tion may enter into the world within two or three days 
of the first, and that the fifteenth generation, if no 
destruction took place, would amount to— 
68,122.318,582.951,682.301,000.000,000.000,000. 
“ Even slow-breeding man has doubled in twenty-five years, and 
at this rate, in less than a thousand years, there would literally 
not be standing-room for his progeny. . . . The elephant is 
reckoned the slowest breeder of all known animals, and I have 
taken some pains to estimate its probable minimum rate of natural 
increase. It will be safest to assume that it begins breeding when 
thirty years old, and goes on breeding till ninety years old, bringing 
forth six young in the interval, and surviving till one hundred 
years old. If this be so, after a period of from 740 to 750 years, 
there would be nearly nineteen million elephants alive descended 
from the first pair.”—(Origin of Species, p. 57.) 
These illustrations will enable us to understand what 
the fact of increase in a geometrical ratio would be, if 
it were realised in the organic world. But we must 
remember that this tendency is never, or very rarely, 
realised. The law of geometrical increase is arrested 
more or less by other principles which keep it in check; 
so that what we have to reckon with is a potential, 
rather than an actual, increase in a geometrical ratio. 
If we consider the conditions which would be necessary 
to secure the actual increase, we shall see at once how 
very improbable it is that it will be often realised.