On Some Interactions of Organisms . 
9 
crease beyond the highest possible limit, but will reach it 
and there stop. The average amount of food will there- 
fore be less than it might be if the species dependent upon 
it did not oscillate — and, the food being less, the average 
number of the species itself must be smaller. Our problem 
is, therefore, to determine how these innumerable small 
oscillations, due to imperfect adjustment, are usually 
kept within bounds — to discover the forces and laws 
which tend to prevent either inordinate increase or de- 
crease of any species, and also those by which widely os- 
cillating species are brought into subjection and reduced 
to a condition of prosperous uniformity. We may know 
in general that such laws and forces are constantly at 
work, and that the tendency of things is towards this 
healthful equilibrium, because we see substantially such 
an equilibrium widely established and steadily main- 
tained through long periods of time, notwithstanding the 
great number and kaleidoscopic variability of the forces 
by which each species is impressed. But this idea will 
repay more detailed elucidation. We will notice, first, 
some of the checks upon injurious oscillations arising out 
of the laws of the individual organism, and afterwards 
those which are brought to bear upon it from without. 
It will at once be seen that, in any case, the maladjust- 
ments possible are of only two kinds — the rate of repro- 
duction in the species must be either relatively too small 
or relatively too great. If it be relatively too small, if the 
species bring forth fewer young than could mature, on 
the average, under existing circumstances, whatever may 
be the oscillations arising, they will tend to disappear with 
the disappearance of the species. The average numbers 
of such a species being, in the most favorable event, less 
than they might be, it will be at a certain disadvantage in 
the general struggle for existence — it will eventually 
yield to some more prolific species with which it comes in 
competition. If, for any reason, its rate of multiplication 
be or become too high, the law of the antagonism between 
individuation and genesis will constantly tend to bring it 
within the proper limit. Reproduction being more active 
than is necessary, the individual force and activity will 
be less than it might be — the species will be at a disad- 
