Living is a confused thing at best, and a thorough understanding either of human nature or of social phenomena is hardly possible until some phases of the actual interfunctioning of the forces analytically studied by the various human sciences has been mastered. Hence this section, in which (1) the constitution of the germ plasm, (2) organic needs, and (3) social continuity are discussed in order to exhibit a few of the interconnections empirically exhibited by "physical," "biological," and "sociological" factors.

(1) The constitution of the germ plasm. According to contemporary biological theory, the direct line of biological connection between parents and children is through the germ cells of the parents. The assemblage of traits which the child receives from his parents-i.e., his heredity-is held to be determined by the precise constitution of the germinal materials which they contribute to his being. Into the nature and extent of this determination we must now inquire.

It has been established that carry within their germ cells nuclei minute material particles, and that these particles (which are usually called "determiners") in some as yet unknown manner affect the course of biological development. Whether two germ cells ever contain exactly the same complement of determiners is not known; but it seems beyond question that the general make-up of the germ plasm as respects determiners differs very widely from person to person, if not from germ cell to germ cell within the same person. The specific heredity of an individual, then, depends on the nature of the germinal materials furnished by its parents, and on the manner in which these materials combine at the moment of fertilization. The determiners act upon each other according to laws whose nature was first indicated by studies made on the common vegetable pea by Gregor Mendel, an Austrian monk; and the science of biology was entirely revolutionized as a result of the discovery of his work in 1900, after it had lain fallow for thirty-five years in an obscure scientific periodical.2 While no description of the complicated processes involved need be offered here, the following observations are pertinent to

the point in hand: (a) all bodily traits exhibited by an individual (as for instance the color of his eyes, shape of his nose, length of his fingers, etc.) apparently possess an indispensable biological basis in determiners (or groups of determiners) derived from the germ plasm of one or both parents; (b) determiners corresponding to each bodily trait exhibited by an individual must be present in the germ cells which eventually mature within the body of that individual, though all of the determiners responsible for all of the bodily traits will seldom if ever be present in any single germ cell; (c) determiners for other traits than those exhibited in the body of the individual will also be present in his germ cells when they finally mature, and under appropriate conditions may therefore be inherited; (d) for reasons that remain obscure, from time to time there appear in the germ plasm new determiners (or combinations of determiners) capable of yielding new inheritable traits. These new traits are called mutations.

To the contemporary biologist the line of hereditary descent is from germ cell to germ cell, each fertilized ovum eventually producing new germ cells whose nature is almost completely unaffected by what happens to all the other cells in the course of their development.* Or, to answer the old question about the chicken and the egg, the egg comes first, and produces both the chicken and additional eggs, which have in turn the power of producing yet other chickens and eggs. The chicken, as Samuel Butler was fond of putting it, is only an egg's way of making other eggs. From the biological point of view it is often legitimate to regard the body as merely the carrier of the germ plasm.

Heredity is often erroneously conceived of as furnishing the raw materials of growth and development. These processes, however, as we have seen, are metabolic; growth does not come about through the mere expansion of already existing structures, but through the intake and assimilation of

*The discontinuity between the germ cells and the body is not absolute, since certain conditions in one or both of the parents (as alcoholism or syphilis) are capable of affecting the germ plasm. In addition, evidence of varying degrees of authenticity is accumulating in favor of the inheritance of acquired characters in certain very specific instances.3

materials furnished by the environment. The world is thus built into the developing organism, while at the same time the organism is built into the world. The structure and functioning of a developed human being is as much an expression of "outside" physical and social forces as it is of "inside" hereditary and organic conditions. Heredity may be regarded as furnishing the limits within which individual development, as elicited by the social and physical environment, takes place. No study yet made, however, has disclosed the exact limit of biological capacity of any individual with respect to any single trait. As a matter of fact, no satisfactory enumeration of distinct biological traits seems possible at the present time so far at least as the human being is concerned. An increasing body of evidence tends to show that the germ plasm does not contain single simple determiners which press relentlessly on to the development of specific bodily traits, provided the environmental conditions. be favorable; but rather that these traits are caused by the coworking of comparatively large numbers of determiners under the precise environmental conditions present at the time when the traits in question begin to appear. Under different conditions the same set of biological determiners would produce a different individual. It is clearly unwise, therefore, to regard heredity as an entity or force when it is taken in abstraction from a supporting and eliciting environ

ment.

From the above it appears that the environment is effective in helping to determine the direction of biological development. Is the constitution of the germ plasm itself ever altered by environmental pressures? This is a very different question. Modern biologists practically without exception have held that the germ plasm lives its own life in an almost complete (if not splendid) isolation, and that its nature remains unchanged, or almost entirely so, irrespective of the life history of the individual in whom it resides. A group of individuals, from the biological point of view, might rather be considered as an aggregate of germ plasms incidentally carried in separate persons than as a collection of persons. The persons may be what they are largely or

even entirely because of environmental influences (these biologists would say), but the germinal materials they carry within their bodies are quite beyond the reach of external influences.

It is not necessary to assume that the physical and social environment has a direct influence on the germ plasm in order to show that biological "determiners," no less than the bodies in which they are found, are responsive to environmental pressures. The group is able to affect the germ plasm indirectly, by processes of selection. Any social activity which picks its participants will turn the trick, provided the selected group also shows a higher or a lower birth rate than the average for the time and place. For, as we have seen, the presence of bodily traits in the members of a group is an index to the presence of germinal determiners in the germ plasm of the members of that group; and a higher or lower birth rate for that group will therefore tend, if the environmental situation remains constant, to perpetuate or to destroy the group, with its germinal determiners.

Many social arrangements have precisely this effect. Perhaps the most obvious instances are to be found where persons belonging to certain restricted groups are either discouraged or prohibited from having children. Members of religious orders in many societies are in this position, as are teachers in our own culture. Alterations in the constitution of the germ plasm of a group are also achieved whenever a selected, group of persons is subjected to an unusually high death rate during the years when its members are still biologically fertile. This happens in our society in the case of those who go to war, as likewise with respect to those who live in unfavorable social environments or engage in dangerous occupations.

The cases cited by no means exhaust the instances where the social environment indirectly determines the biological constitution of the group. The selection of bodily traits among the young when at all severe inevitably means the selection of germ plasm, since the traits which make their appearance in the body, and are selected, also go to make up the determiners in the germ plasm (together, of course, with

those traits which according to the laws of heredity fail to appear in the body). And the group is continually engaged in this process of selection, according to canons and standards which differ widely from place to place. Rules and understandings always exist which determine how groups and individuals shall come to meet each other; who shall marry whom, and under what conditions; how many children there shall be, and at what times in the parents' life cycles; which children shall be favored, and in what ways; etc. Who shall be born and who shall live and come to maturity, and under what conditions, are thus not pure questions of biology. These matters also depend on the prevailing social arrangements, and on the ideas current in the group at any given time. The infant is not only born helpless and immature into a social group. In a very real sense he is born of the group. He is its child quite as truly as he is the child of his parents.

We are beginning to see that the chief biological difference between the germ plasm and the body is that the former includes within itself the possibility of a considerable number of traits not actually displayed in the body. This means that every new generation offers a new deal, so that it is really in part possible for the group to decide whether the new hand shall be played in the same old way. Neither the individual nor the group, however, has done much up to the present so far as the conscious and deliberate selection of biological traits to be exhibited by the coming generation is concerned. It is to be doubted whether we possess sufficient detailed information at the present time to carry out any extensive program of eugenics, or efforts to improve our biological stock. In breeding out traits which were regarded as undesirable, as, for example, certain neurotic tendencies, we might find ourselves committed to the extinction of other associated qualities of great social importance, as perhaps some kinds of artistic ability. No very positive measures seem feasible in the present state of our knowledge. At the same time, some students of the subject have suggested that the human stock might be improved by discouraging childbearing among: (a) the feeble-minded and others of less intelligence; (b) the