1906. Moffat. — The Struggle for Existence, 
97 
case — it does not really matter whether the individuals of this 
or that species suffer from other perils besides scarcity of 
necessaries or not. That is, it does not matter except to the 
mere individual. An animal may be very largely exposed to 
the ravages of beasts and birds of prey ; but these ravages, 
unless they are on such a scale as would in a few years exter- 
minate the animal, will have no other effect than to ease the 
situation for the survivors by slackening the competition 
among them ; so that, in the next season of scarcity, fewer 
will die, and, when that season is over, there should be the 
same total number of individuals living as if the beasts and 
birds of prey had taken none. 
The same may be said of other forms of peril to which 
animal life is undoubtedly exposed. For example, birds when 
on their migration suffer many calamities, the weaker species 
often dying of fatigue, while those of stronger flight, like the 
swallow, however fairly they get over their journey in an 
average season, must now and then be overtaken by tempests 
in which case, of course, the destruction of life is enormous 
But this sort of destruction does not tend to affect the per- 
manent numbers of the species. There is still, in every 
average j-ear — according to our high-water mark conception — 
a margin left over of birds that must die from competitive 
causes ; and the fewer the storms destroy the greater must be 
the mortality among the survivors, so that next year the 
numbers will still be the same as if there had been no storm. 
In an exceptional year, of course, the destruction might be so 
great that no competition among the survivors would be 
necessary; but even in that case, if we accept Darwin's'law as 
to the nature of the limit to multiplication, the loss would very 
soon be made up, probably in the course of the next breeding 
season. Whenever the numbers fall below the high-water 
mark, competition is practically suspended until they have 
reached it again ; and this, on Darwin's supposition, will in 
the case of any but a very slow-breeding species occur very 
soon. 
Now, Dr. Weismann's highly original views on this subject 
are conveyed in his interesting essay on the " Duration of 
lyife," from which it appears plain that he looks on every 
species of animal as limited in its numbers by the very set of 
A 4 
