But is this analogy valid? It is from the vegetable and animal kingdoms that man’s food is drawn, and hence the greater strength of the reproductive force in the vegetable and animal kingdoms than in man simply proves the power of subsistence to increase faster than population. Does not the fact that all of the things which furnish man’s subsistence have the power to multiply many fold—some of them many thousand fold, and some of them many million or even billion fold—while he is only doubling his numbers, show that, let human beings increase to the full extent of their reproductive power, the increase of population can never exceed subsistence? This is clear when it is remembered that though in the vegetable and animal kingdoms each species, by virtue of its reproductive power, naturally and necessarily presses against the conditions which limit its further increase, yet these conditions are nowhere fixed and final. No species reaches the ultimate limit of soil, water, air, and sunshine; but the actual limit of each is in the existence of other species, its rivals, its enemies, or its food. Thus the conditions which limit the existence of such of these species as afford him subsistence man can extend (in some cases his mere appearance will extend them), and thus the reproductive forces of the species which supply his wants, instead of wasting themselves against their former limit, start forward in his service at a pace which his powers of increase cannot rival. If he but shoot hawks, food-birds will increase, if he but trap foxes the wild rabbits will multiply; the honey bee moves with the pioneer, and on the organic matter with which man’s presence fills the rivers, fishes feed.