The mode of the existence of units is defined by a multitude of conditions. There are, on the one hand, inherited conditions, resulting from the adaptation previously created during thousands of years, not only in one of the genetic units, but in all the genetic units which entered into the process of crossing within the given unit; and on the other hand, present conditions of milieu, in which the unit is living. The milieu is not a simple one: it consists of conditions beyond the control of man, which may be called primary milieu; conditions created by man, which are essentially a product of culture, or secondary milieu; and conditions which are formed by other ethnical units in the midst of which the unit is living, called here tertiary, or interethnical, milieu. Every ethnos adapts itself to the complex of milieus with its aptitudes resulting from the accumulation of physical peculiarities and experience transmitted through tradition. Yet the ethnos itself forms one of the elements of the milieu, and it is partly responsible for the existence of the interethnical milieu — it is a part of a system. The ethnos is thus a result of equilibrium which exists between the phenomena. Therefore the ethnos, regarded as an isolated phenomenon, is a mere and dangerous abstraction.
From the observation of facts one comes to the idea that the existence of ethnoses is conditioned and regulated by a system of equilibrium. The internal equilibrium of the ethnos is defined by its number (population), its degree of adaptation expressed in its culture, and the physical adaptation and territory occupied. When symbolized, it is ω = q/TS, where ω is the constant of ethnical equilibrium, q is the number of the population (with corrections as to the age and sex), S is the biological adaptation in the form of culture and functional power, T is the territory (with the corrections as to the utility, latitude, altitude, climate, etc.) [12].
The unit may exist only on condition of the preservation of equilibrium — the constant of ethnical equilibrium. If there is any change in the elements forming this equilibrium, the impulse of variation of other elements will appear. Positive and negative impulses may also naturally appear, for the elements may increase and decrease. For instance, the decrease of territory may produce either a positive increase of S or a decrease of population; the decrease of population may result in a decrease of territory, and a decrease of culture, or one of them, and so on; so that the preservation of ethnical equilibrium is a source of permanent variations of elements. I say permanent, for there are at least two conditions which are permanent sources of variations of one of the elements of equilibrium. These conditions are: a prompt change of climatic conditions and their periodical fluctuations, to which the unit must adapt itself; and there is an interethnical and inter-species pressure coming out of the neighbouring ethnoses and other animals. In fact, the interethnical milieu also forms a system of equilibrium. I will now give a rough instance. Let us suppose that an ethnos is in the process of numerical increase. It thus needs some new territory for the surplus of population. The spreading of the population is met with the opposition on the part of other ethnoses, so it may take the form of war, which requires a certain technique for defense which again implies a certain complication of the economical and social organization. The pressure on the part of neighbours also takes a form of cultural influence in its various aspects.
The opposition to the pressure must be equal to the pressure felt by the ethnos, if the latter wants to preserve its existence and territory; and it must be higher than the pressure, if it tends to spread over the territories occupied by neighbours or wants to imply the adoption of its own cultural elements or the whole complex. So an independent existence of an ethnos may be realized on the condition of maintaining a constant equilibrium formed by the opposing pressure of an ethnos to the pressure of all neighbouring ethnoses. However, since the changes which occur in one of the ethnoses result in the change of its internal equilibrium and ethnical value, the interethnical equilibrium will always vary, which implies adaptation and variations in ethnoses. In this way, the interethnical pressure forms an almost constantly acting impulse of variations of ethnical equilibrium, whence result variations of elements constituting this equilibrium. The interethnical pressure is one of the greatest sources of variations, as it is in other animal species competing and cooperating between themselves. Without interethnical pressure the ethnos is doomed to «vegetation.» We know practically no ethnoses living beyond the interethnical pressure. The cases of extinct Tasmanians and living Eskimos are instances of isolated groups observed by travellers, but there is no little doubt that prior to their discovery they lived under the pressure of their former neighbours. Here it may be noted that, although the ethnos always tends to avoid interethical pressure, it cannot successfully survive without this pressure, when meeting other ethnoses which are under interethnical pressure.
The cultural variations, as implied by internal causes (e. g., increase or decrease of population), or external causes (e. g., interethnical pressure), appear either slowly or promptly. They may be maintained during a shorter or longer period with equal or varying intensity. These reactions on the change of ethnical and interethnical equilibrium depend on the ability of the ethnos to react on milieu. Yet, in the process of adaptation, the ethnos may accept various ways of self-defence; e. g., it may change its physical features, its culture, or it may increase its number, or reject by force any pressure, etc. All depends on the way and degree of adaptability and self-consciousness of the unit.
The changes require a certain effort, psychic and mental, which is proportional to the impulses of variation. Yet the tension felt by the ethnos depends upon the period in which the changes occur and the ability of reacting. With the increase of interethnical pressure, and with the increase of impulses of variations, the tempo of changes increases. It is thus natural that the shorter the period in which changes occur, the higher the tension. As a matter of observation, the tempo of variations is always increasing, for the impulses of variations and interethnical pressure are always increasing. It is sufficient to remember that the powerful factor of interethnical pressure — population pressure — is always increasing. If at a certain moment it attains such a velocity that the possible tempo of variations cannot be sufficient for assuring the maintenance of equilibrium, the interethnical clash occurs and the equilibrium breaks down. The increase of tempo of variations is one of the most characteristic features of the present phenomena, but it does not go parallel with the increase of the possibilities of reactions amongst the ethnos, so that it menaces the existence of the ethnoses more than ever before. In fact, the dissolution, absorption, re-dissolution, and re-absorption of the ethnoses is so common that the new changes sometimes may be observed during a man's life.
12. In spite of the great simplicity of the nature of this equilibrium in ethnoses, and in spite of the simplicity of a series of logical consequences resulting therefrom, it has never been systematically analysed. Early work on the problem of population and correlation of cultural and other phenomena characteristic of the ethnos in 1912 led me to the idea of binding this relationship into the simple formula shown above. It may here be noted that the idea of such a relationship was formulated during my first travelling in Siberia when I saw a series of ethnical groups showing the same kind of equilibrium, but existing under different conditions. The field observation of other groups during following expeditions (1913-1918) has strengthened the impression of actuality of such a relationship, which was naturally supported by well-known facts from historic records, and by observations of other travellers. In the courses of lectures delivered in the University of Vladivostok (1918-1922, with an interruption) I applied the theory of ethnos for the analysis of ethnical relations. In 1922 I formulated it in a published form («Place of Ethnography Amongst the Sciences and Classification of Ethnoses,» Vladivostok, 1922, in Russian), and in the same year expounded it in a special work devoted to the variations of ethnical and ethnographical phenomena («Ethnos. Fundamental Principles of Variations of Ethnical and Ethnographical Phenomena,» Shanghai, 1923, actually published at the end of 1922). Two chapters of this work were translated into English and published in 1924 («Ethnical Unit and Milieu,» Edward Evans & Sons, Shanghai, 1924), which received a certain circulation and was reviewed in several leading periodicals (e. g., in Nature, London, La Giographie, Paris, and others). This theory has also been developed from the biological point of view in my new work «The Process of Physical Growth,» which will soon be published. My hope that the criticism might help me in my further work has not yet been realized. By way of some encouraging reviews, one of my critics has, I think bona fide, declared my theory to be a kind of «mysticism»; and another, who happened to be still less prepared for accepting it, styled it as «une farce.» On the other hand, I find that in 1924 R. Pearl («Studies in Human Biology,» Baltimore, p. 567, et seq.) put as the basis of his theory the relationship between the density and culture as a postulate, and A. Lotka («Elements of Physical Biology,» Baltimore) in 1925 touched upon this idea in his study of equilibria. Unfortunately, these two authors did not develop further consequences. In the same order of ideas are Schmoller's calculations of the density of population in its correlation with the economic system. F. Boas, in his recent work («Anthropology,» in «Encyclopaedia of Social Scieces,» New York, 1930), formulates thus: «The density of population is determined both by cultural achievements and by environment»; furthermore, a «correlation between density of population and diversity of cultural traits may be observed,» and «political organization depends upon the size of social units and upon the density of population» (id., pp. 99, 100). Indeed, in this deterministic form, which calls to mind the methods correlated with the old conceptions of «evolution» and «progress,» economical determinism, etc., F. Boas's treatment of this equilibrium is extremely confusing and undesirable. As a matter of fact, social systems, and particularly political organizations, are functions of adaptation, and we have many examples of entirely different social systems and political organizations amongst the ethnoses who have the same density and the same political systems are found amongst the ethnoses possessing a different density of population. The question thus cannot be so simplified. From the above-quoted facts it may be seen that the idea of such an equilibrium is already «in the air.»