The idea which permeates Darwin’s work is certainly one of real competition going on within each animal group for food, safety, and possibility of leaving an offspring.  He often speaks of regions being stocked with animal life to their full capacity, and from that overstocking he infers the necessity of competition.  But when we look in his work for real proofs of that competition, we must confess that we do not find them sufficiently convincing.  If we refer to the paragraph entitled “Struggle for Life most severe between Individuals and Varieties of the same Species,” we find in it none of that wealth of proofs and illustrations which we are accustomed to find in whatever Darwin wrote.  The struggle between individuals of the same species is not illustrated under that heading by even one single instance:  it is taken as granted; and the competition between closely-allied animal species is illustrated by but five examples, out of which one, at least (relating to the two species of thrushes), now proves to be doubtful.(32) But when we look for more details in order to ascertain how far the decrease of one species was really occasioned by the increase of the other species, Darwin, with his usual fairness, tells us: 

“We can dimly see why the competition should be most severe between allied forms which fill nearly the same place in nature; but probably in no case could we precisely say why one species has been victorious over another in the great battle of life.”

As to Wallace, who quotes the same facts under a slightly-modified heading ("Struggle for Life between closely-allied Animals and Plants often most severe"), he makes the following remark (italics are mine), which gives quite another aspect to the facts above quoted.  He says: 

“In some cases, no doubt, there is actual war between the two, the stronger killing the weaker. but this is by no means necessary, and there may be cases in which the weaker species, physically, may prevail by its power of more rapid multiplication, its better withstanding vicissitudes of climate, or its greater cunning in escaping the attacks of common enemies.”

In such cases what is described as competition may be no competition at all.  One species succumbs, not because it is exterminated or starved out by the other species, but because it does not well accommodate itself to new conditions, which the other does.  The term “struggle for life” is again used in its metaphorical sense, and may have no other.  As to the real competition between individuals of the same species, which is illustrated in another place by the cattle of South America during a period of drought, its value is impaired by its being taken from among domesticated animals.  Bisons emigrate in like circumstances in order to avoid competition.  However severe the struggle between plants—­and this is amply proved—­we cannot but repeat Wallace’s remark to the effect that “plants live where they can,” while animals have, to