§ 12. Limit of the food supply. These myriads of seeds seeking for a chance to germinate, these myriads of young in every species seeking to survive, can not possibly grow to maturity. Even the slow-breeding elephant, with a period of gestation of three years, and producing one calf at a birth, would cover the entire earth and leave no standing room in a few centuries if every calf born could live to maturity. In how much briefer time would the fast-breeding animals and insects cover every foot of the earth! The limit of the food supply alone would prevent this. This has been demonstrated repeatedly when herbivorous animals have been placed on an island from which they could not escape, and where there were no large beasts of prey. This demonstration was made on an enormous scale when the rabbit was introduced into Australia, that peculiar and long isolated continent containing none of the rabbit's ancient enemies. The rabbits increased and devastated great areas, and tho they have been hunted, trapped, and poisoned by the millions, and great numbers of them have died of starvation outside the wire fences erected to stop their progress, they still continue to be a pest. If there were no other limit earlier interposed, this ultimate limit of the food supply would quickly check the increase of any form of animal life.

§ 13. Eater and eaten. The destruction of one kind of animal by another limits numbers in another way. The number of lions is limited by the number of their prey in the region where they roam. The number of deer, therefore, is limited in two ways, by the amount of their food and by the number of lions which catch the deer. The more numerous the lions, the fewer the deer; the fewer the deer, the greater the supply of vegetable food; as the pressure increases on one side, it decreases on the other, until an equilibrium is reached. Some carnivorous animals will in times of great hunger eat the weaker members of their own species, even their own young. The actual limitation here is thus not starvation, but violence induced by hunger.

Geology tells the story of a slow and steady change that has gone on in the earth and in the species of animals that inhabit it. History records some rapid changes due to convulsions of nature or to interference by man with the natural conditions. But the usual condition is an equilibrium of numbers, long maintained. Tho each species of animal has a capacity for unlimited multiplication, throughout nature each keeps its customary place, changing little despite its efforts to increase and to crowd into the habitat of other species.

§ 14. Features of the biologic stage. Every species of animals thus presents the problem of the adjustment of numbers to environment.3 Among wild animals this adjustment is in the biologic or instinctive stage, which is characterized by these features: (a) A physiological factor, the physical capability of developing reproductive cells, and of nourishing and protecting them up to the time that they become separate living beings through various processes in the oviparous and viviparous animals, (b) A psychological factor, the instinct of reproduction impelling to the realization of this physiological factor, (c) An absence of any knowledge or understanding of the relation between the instinct and the birth of offspring, and consequently the lack of any attempt to restrain or regulate the birth rate, (d) "The physiological maximum birth rate," being the number of births relative to the number of individuals capable of reproduction, that results from the unhindered operation of the two prime factors, physiological and psychological, (e) A certain degree of parental care after birth, normal to each species, to help the young through the early period of life, (f) The survival of the individuals thereafter depending on their inherent strength, vigor, and habits of life (including gregariousness and cooperation), and on the objective conditions of accidents, disease, food supply, rivals, and enemies.

3 This is sometimes for convenience called the problem of "population," altho this is taking liberties with the derivation from populus, people.

§ 15. Primitive populations in the biologic stage. The long life of the human race on this globe has been spent almost entirely in this instinctive stage of population. In many savage tribes when first visited by European travelers, the physiological maximum birth rate seems to have been nearly attained. In some tribes it was well nigh normal that a woman of forty years of age had given birth to twenty children - yet those tribes had only a stationary population. Every Esquimau girl is married in her 'teens and carries a baby on her back each summer, yet the population of Esquimaux does not increase. To the simpler native peoples even to-day the nature of birth is a mystery (paragraph (c) above). A recent scientific observer of the Australian tribes found them still in this state. Every girl is married, and every widow is remarried within six weeks after the death of her husband. This is the biologic stage of population, remarkable in that with a maximum birth rate the total population is either stationary or merely rhythmically changing.

Few human societies known to us are so primitive that they have not passed this stage, but many societies have risen only little above it. In most savage tribes, where starvation, disease, and war are constantly at work, the difficult task is to maintain the population. The birth rate is enormous, but few of those born arrive at maturity. It would be hazardous to tribal existence under these conditions to limit the birth rate. The custom of the adoption of captives from hostile tribes is wide-spread, because the efficiency - the very survival -of the tribe depends on keeping up its number of warriors.

§ 16. War and the pressure of population. War is the normal condition of most primitive tribes. Its cause usually appears to be standing feuds and ancient enmities, but the deeper and abiding economic cause is the struggle for hunting grounds, for pasturage, and for control of natural resources. When resorting to war as the rude remedy for over population, mankind is hardly above the animals, who fight for food against other species of animals or against their own kind. Hunting, fishing, or pastoral people, or those in the earlier stages of agriculture, require a large area for a small population. Distant excursions and frequent forays, when food fails, develop rival claims to favored districts, and war is the only settlement. Fighting under these conditions is an activity of such economic importance that much of the energy of the tribe must be strenuously given to it. The ceaseless loss of life in savage wars is almost incredible to modern minds. The successive invasions of the Roman Empire by the Teutonic tribes, and the later inundations of medieval Europe by the fierce pastoral tribes of central Asia, were undoubtedly due to the increase of population and the outgrowing of resources by these barbarian peoples, or to the failure of their food supplies because of seasonal or of climatic changes.

Note

Definitions. Statics (status, state, stationary) is that phase of a science which has to do with an equilibrium which must result in time from the existing group of forces, operating in unaltered magnitude. Dynamics (dynamic force, movement) is that phase which has to do with the changes in process as the result of new or stronger or weaker forces, which are more or less permanently unsettling the static equilibrium and are carrying the point of normal equilibrium itself to higher or lower levels. The terms static and dynamic in economics, therefore, may be applied to forces, prices, equilibriums, problems, situations, and economies (altho the forces may meet with increasing resistance that at length puts a limit to their effects, as the resistance of a spring balance checks the weight at a certain point). The change may be either progressive or retrogressive, and a higher or a lower level may be reached and maintained until some quite different force coming from another direction is operative. There are changes that in a brief view appear to be cumulative, which on longer study are seen to be rhythmic. Again and again men have been forced to revise their judgments, either hopeful or discouraging, of current tendencies, after time had enabled them to see a larger segment of the curve of change returning to its former level.