47 
“ There is no exception to the rule that every organic being 
naturally increases at so high a rate that if not destroyed the 
earth would soon be covered by the progeny of a single pair.”— 
(Origin of Species, p. yi.) 
But there is great virtue in that “if”: nor is this the 
only condition necessary. Professor Huxley has calcu 
lated that a single plant would occupy every available 
spot of the globe before the end of the ninth year: but 
of course this must take place under peculiarly favourable 
and well-nigh impossible conditions. We must suppose 
that there are no rivals, and that the dry land of the 
globe consists of the same kind of soil and has the same 
kind of climate, and that the conditions are everywhere 
the same and exactly suited to the plant. If no organ 
isms were prematurely destroyed, if a species had no 
rivals, if external conditions were uniformly favourable, 
if-all available spheres of life on this globe were accessible, 
then indeed we might see an increase in a geometrical 
ratio—until the earth could hold no more. There is 
surely great virtue in an “if”! but as a whole “litany 
of ifs ” would not avail to realise the dream of un 
checked fertility, it is rather a work of supererogation to 
enter upon elaborate calculations of a strictly hypothetical 
increase, which can never possibly take place on this 
earth of ours. 
Mr. Wallace has a curious way of speaking of organic 
increase in a geometrical order. He seems to consider 
that it is possible that it should take place in connection 
with a fixed population :— 
“ As all wild animals increase in a geometrical ratio while their 
actual numbers remain on the average stationary, it follows that 
as many die annually as are born.”—(Contributions. p. jop.) 
“ We must never for an instant lose sight of the fact of the 
enormously rapid increase of all organisms, which has been illus 
trated by actual cases, given in our second chapter, no less than