18 THE DARWINIAN HYPOTHESIS 1 
live at the expense of some other animal or plant, 
but the very plants are at war. The ground is 
full of seeds that cannot rise into seedlings; the 
seedlings rob one another of air, light and water, 
the strongest robber winning the day, and ex- 
tinguishing his competitors. Year after year, the 
wild animals with which man never interferes are, 
on the average, neither more nor less numerous 
than they were ; and yet we know that the annual 
produce of every pair is from one to perhaps a 
ON appa dpia, Salis 
million young; so that it is mathematically certain — 
that, on the average, as many are killed by natural 
causes as are born every year, and those only escape 
which happen to be a little better fitted to resist 
destruction than those which die. The individuals 
of a species are like the crew of a foundered ship, ; 
and none but good swimmers have a chance of 
reaching the land. 
Such being unquestionably the necessary con- 
ditions under which living creatures exist, Mr. 
Darwin discovers in them the instrument of natural 
selection. Suppose that in the midst of this in- 
cessant competition some individuals of a species 
(A) present accidental variations which happen to — 
fit them a little better than their fellows for the 
struggle in which they are engaged, then the 
chances are in favour, not only of these individuals 
being better nourished than the others, but of 
their predominating over their. fellows in other 
ways, and of having a better chance of leaving 
