i. Cultural DiffusionRobert Heine-Geldern
ii. The Diffusion of InnovationsTorsten Hägerstrand
iii. Interpersonal InfluenceElihu Katz
Diffusion means the spread of culture from one ethnic group or area to another. Various definitions have been proposed in order to distinguish between diffusion and acculturation; the difference is one of continuity and intensity of contact. Acculturation generally involves prolonged contact of whole culture complexes and may be unilateral or bilateral.
Diffusionism in ethnological theory
As early as the fifth century b.c., Herodotus noted examples of diffusion, but it was the discovery of America that stirred intellectual discussion and speculation. Had the cultures of the New World developed independently, or had they been imported from the Old World? From the sixteenth to the eighteenth century numerous authors supported the diffusionist view, but their more or less naive writings, based on totally insufficient data, did not carry conviction. The prevailing trend in European science favored a theory of natural laws, which were thought to govern human progress and to produce similar results in the various regions of the earth. These ideas were clearly formulated in the eighteenth century and culminated in the nineteenth century in the evolutionist school of anthropology. At the same time truly scientific treatises on the diffusion of culture traits began to appear. One of the first was Alexander von Humboldt’s brilliant attempt to prove the Asiatic origin of the Mesoamerican calendric systems. Even the evolutionists did not deny that diffusion had played a certain role in the development of culture, although they minimized its importance. One of the most prominent, Edward Tylor, wrote several excellent papers in which he demonstrated the diffusion of various culture traits.
Around 1890 a reaction appeared in Europe and America against the logical inconsistencies of the evolutionist theory. Franz Boas in the United States, Gabriel Tarde in France, and Friedrich Ratzel in Germany stood up as its critics, all of them stressing the importance of diffusion. Scandinavian archeologists showed that the development of the Bronze Age in Europe was influenced by cultures of the Near East and the Mediterranean regions. They thus started a trend which ever since has been important in prehistoric research. Fritz Graebner (1911) wrote the first systematic treatise on the theory of diffusion, and many important studies were made tracing the diffusion of single traits, such as the plow, whole complexes of metallurgical technique, and the spread of basic cosmological ideas and corresponding religious practices. The most important studies of the processes of diffusion, however, were made by American anthropologists. It is to them, even more than to Graebner, that we owe the theoretical foundations for the appraisal of diffusion in its various aspects.
The processes of diffusion
Although whole cultures may spread as a result of the migration of their bearers, a culture is practically never adopted by other ethnic groups without considerable change and selection of traits. This applies also to diffusion on a minor scale. Whether a particular trait is accepted depends not only on its utility to the borrowers but even more on whether or not it can be integrated into the receiving culture. The borrowing of more elaborate utensils and techniques and of sophisticated ideas presupposes a complex socio-cultural level on the part of the borrowing people. Nomadic hunters may turn with relative ease to some kind of primitive shifting agriculture but will hardly be inclined to prepare permanent fields with all that this implies with regard to change in mode of life. The diffusion of elements of social structure encounters greater difficulties than that of material or religious traits. Among some peoples of southeast Asia and among the Tuareg of the Sahara, matrilineal forms of society, although unorthodox from the point of view of Islamic law, survived even conversion of these people to Islam. In general, however, the conversion to one of the higher religions is invariably accompanied by the acceptance of numerous other culture traits—such as script, types of behavior, modes of dressing and housing, laws, and forms of government—and is one of the most potent factors in diffusion. Prestige, too, plays an important role. Traits have been borrowed merely for the sake of prestige, even though they are detrimental to the borrowers’ hygiene or economy. The adoption of European clothing by peoples in the tropics is a case in point.
Negative selection, i.e., the rejection of certain cultural items, may be due to their incompatibility with firmly established customs, with the prevailing social structure, or with religious tenets and usages. Mere habit and the addiction to the traditional way of doing things are no less powerful sources of resistance to innovations. Frequently, however, no particular reason can be detected that could explain why one foreign trait was accepted and another not. In many instances “traits spread erratically and unpredictably” (Dixon 1928, p. 120).
The more traits a people has already borrowed from another, the easier will be the acceptance of additional traits. Traits that at first were rejected may then be adopted since they no longer conflict with those of the receiving culture, which has already been modified. Occasionally, the diffusion of even a single culture trait may have far-reaching consequences. The introduction of firearms, for instance, necessitated a change in the type of warfare, and this, in turn, affected the social structure of Europe. When the Tanala in Madagascar borrowed from their neighbors the trait of planting rice on irrigated terraces and abandoned the slash-and-burn type of shifting agriculture, a complete transformation took place, not only of their rules of land tenure, but of their social and political organization (Linton 1936, pp. 348–354).
Borrowed elements of culture usually undergo some kind of change or adaptation. We need only think of the innumerable variations, from tribe to tribe, when techniques of pottery-making, metallurgy, and weaving have been diffused. Gothic art was not the same in Germany and Italy as in France, nor was the Hindu and Buddhist art of Java identical with that of India from which it was derived. When the Greeks adopted the old Semitic alphabet, they adapted it to their own language, and new changes took place when the alphabet was transferred to the various peoples of Europe. When a myth spreads from one area to another, details may be lost and new ones may be added to or substituted for the original ones.
Stimulus diffusion. In many instances it is not the actual culture trait that is adopted by the borrowing people but merely the principle on which it is based. This process has been termed “stimulus diffusion.” It must have played an important role in the spread of agriculture and animal domestication. The domestication of the reindeer by Siberian tribes, for instance, was almost certainly due to some aquaintance with the horse and cattle breeding of their southern neighbors. Members of illiterate tribes in Africa, Asia, and America who knew of the existence of the European or Arabic alpha-bets created new systems of writing for their respective languages. The development of Egyptian hieroglyphics probably resulted from some knowledge of the Babylonian script of the Jemdet Nasr period, even though the actual characters of each script are completely different.
Agents of diffusion. The kind of traits transferred from one people to another depends largely on the agents of diffusion—those giving and those taking. The traits will differ according to whether the agents are priests, medicine men, traders or artisans, men or women. Men’s societies and rituals, weapons, methods of hunting and warfare with the concomitant religious and magical practices, such as scalping or head-hunting, can, of course, be disseminated only from men to men. Very often the relative conservatism of women has contributed considerably to cultural diffusion. Where inter group marriage is practiced, the women hold on to their native customs and will transmit them to their children. This is bound to further the diffusion of techniques of pottery and weaving, of ornamental designs, of myths, etc., occasionally even of languages. In some instances the acceptance of new culture traits has been due to the initiative of one prestigious person.
Diffusion may be the result of deliberate actions on the part of the donors. This applies to missionaries of whatever religion and to the founders and promoters of nativistic cults and movements. Conquerors and colonial powers furthered, or even enforced, the adoption of their laws, customs, and techniques. However, even in such cases diffusion was frequently reciprocal. We need only cite the adoption of maize, tobacco, rubber, etc., by the Europeans in America or the flood of Oriental influences that reached Europe as the result of the British occupation of India. If the conquerors were relatively few in number and the culture of the conquered superior to that of the conquerors, the rate of diffusion was occasionally reversed, with the result that the conquerors were more readily assimilated by the conquered, abandoning even their own language and eventually losing their ethnic identity. This happened, for instance, to the Langobards in Italy.
The deliberate initiative of the borrowers may be no less important than that of the donors. In the mid-twentieth century Asians and Africans who study in Europe or America and take home their acquired knowledge are among the principal agents of diffusion. Similar processes have no doubt contributed to the spread of ancient civilizations, even though literary evidence of this is scarce. The visits of Romans to Greece in order to study Greek philosophy and rhetoric, and the pilgrimages of Chinese scholars to India to study the tenets and monastic rules of Buddhism, are cases in point.
Diffusion versus independent invention
Whether the occurrence of similar culture traits among different peoples is due to diffusion or to independent invention and parallel development has been a perennial subject of anthropological discussions. In the past, anthropologists who favored the argument for parallelism referred to the “psychic unity of mankind” and to those natural laws thought to produce similar effects.
Where literate civilizations are concerned, the role of diffusion can usually be determined by historical research. There are still some moot cases— such as the question whether gunpowder and printing were invented independently in Europe or as the result of stimuli derived from China—but wherever we stand on firm ground it is apparent that the independent repetition of inventions has been exceedingly rare, particularly when compared to the enormous effects of diffusion.
Where written sources are not available, the solution of problems of diffusion is frequently more difficult. Independent invention can be proved only rarely, and perhaps never with regard to immaterial culture traits or where perishable materials are concerned. We can be sure that the fine pressure-flaking of stone tools was invented independently in northwestern Australia and not derived from that of the Solutrean culture, since nothing of the kind has been found in the intermediate areas. Cases like this are exceptions. In general we can only try to demonstrate the probability of diffusion, and if this proves impossible, leave the question unanswered. The following criteria of diffusion, first formulated by Graebner (1911), are still applied, with only minor variations, by most anthropologists interested in the subject: the more complex a culture trait is, the more secondary traits it contains that are not essential to its function (criterion of form), and the more similar the traits (criterion of quantity) shared by two areas, the more likely it is that the presence of these traits is due to diffusion.
Loss of traits. In Graebner’s opinion these principles were valid also in the case of discontinuous distribution of traits. Boas and others were reluctant to admit diffusion except where contiguous areas were concerned. There are, however, numerous explanations that can easily account for gaps in the distribution of related culture traits. We need not even refer to those famous and frequently cited cases—the disappearance of the bow, of pottery, and of boatbuilding on several Oceanic islands. These were isolated incidents and of little importance. Of greater significance is the fact that any major culture change, whether due to internal development or to diffusion, is not only bound to add new culture traits but to result in the elimination of others. We need only think of all the appliances, customs, and types of behavior that within a lifetime are replaced by others and become obsolete, but which still survive in marginal areas. This process of elimination has been occur-ring since the Paleolithic. Above all, it was the spread of the higher civilizations, and of Christianity, Buddhism, and Islam, that ripped apart formerly uninterrupted areas of archaic culture traits.
Head-hunting may serve as an illustration. In the Old World during the nineteenth century head-hunting was largely restricted to southeast Asia and Oceania and to some tribes in Africa. Here was a case that clearly seemed to warrant the assumption of independent parallel development. The picture changes, however, when we consult the archeological record, or ancient literature. We shall find that head-hunting was practiced in vast regions of Europe, from the Iberian Peninsula to southern Russia. There are many indications of its having been practiced by tribes in central Asia, and if we extend our research further back in time, we shall find traces of head-hunting in pre-dynastic Egypt and in the ancient Near East. Obviously, the two regions in which head-hunting was found in modern times, even though thousands of miles apart, were mere remnants of an area stretching from the Atlantic Ocean eastward to the Pacific where head-hunting was practiced.
Closing the gaps in distribution. Occasionally, archeology helps to bridge gaps between widely separated areas. For example, a special type of harp, with a boat-shaped body, is found in west and central Africa, in Burma, and in Siberia. This puzzling distribution would seem to defy any attempt to explain it as the result of diffusion had not archeological discoveries shown that the same type existed in ancient Babylonia, Egypt, and India.
In considering the possibility of diffusion the time factor should never be forgotten. Such a custom as that of perforating the lower lip and inserting a plug, found among some tribes in Africa and the Americas, may very well have spread from continent to continent and then disappeared from most of its former area with the passage of time. On the other hand, gaps in the distribution of traits may occasionally be due to rapid migrations. When, in the sixteenth century, a group of the Tupi-Guarani covered the thousands of miles from the Atlantic coast of Brazil to the Andes in ten years and, in the eighteenth century, a Kalmuk horde took nine months for its migration from the Volga to Mongolia, they cannot have left many traces on their way. Such rapid migrations have frequently been observed in historic times. There is no reason why this should not have occurred in prehistoric periods as well. Finally, we must not forget that wherever boatbuilding and navigation were sufficiently developed arts, peoples separated by the sea were in a certain respect neighbors. Given the necessary means of transportation, the same applies to peoples separated by deserts.
Complex traits. In summary, we may conclude that the geographical distance between two similar culture traits, be it ever so great, does not in itself suffice to disprove diffusion, and that in such instances, too, we must rely primarily on the criterion of form. Very simple inventions may, of course, have been made more than once. However, inventions of weaving, of the various metallurgical processes, or of intricate calendrical systems were not single events but the results of whole series of innovations and improvements. The probability of such a series having been repeated in more or less the same order and with similar results is practically nil.
Some reservations must be made with regard to social phenomena, such as sib and kinship systems, marriage rules, totemism, chieftainship, priesthood, etc. There can be no doubt that in these respects, too, diffusion played an important role, but we do not yet know to what extent social trends and psychological factors may occasionally have produced similar, but unconnected, results. The subject has not yet been studied sufficiently on a world-wide basis. Therefore caution in asserting or denying the diffusion of specific social traits is advisable.
The following examples may serve to illustrate some kinds of major problems concerning diffusion that are of anthropological interest.
Megaliths. The widespread distribution of megalithic monuments in the Old World stimulated many fantastic and unsound speculations. In recent times, however, the relevant problems of diffusion have been carefully studied, particularly with regard to areas in Africa, Asia, and Oceania where such monuments are still raised and where their religious and social basis survives. It now appears certain that the custom of erecting megaliths belongs to a socioreligious complex characterized by emphasis on an ancestor cult and genealogy, by wealth and fertility rites, animal sacrifice, and rank-conferring rituals that are thought to ensure for the souls of the performers or recipients a better lot in the hereafter. The original center from which this complex spread has not yet been determined. It lay probably in the Mediterranean area, possibly in Palestine and the surrounding regions, where megalithic monuments have been dated to the fourth millennium b.c. In some instances the megalithic complex spread as a result of migrations, in others by slow diffusion from tribe to tribe. In studying its various aspects, we are dealing with a prehistoric religious and social movement, which over thousands of years spread throughout an area reaching from the Atlantic coast of Europe to Oceania.
Trans-Pacific diffusion. More than any other problem of diffusion, the question of trans-Pacific relations between the Old World and the New agitates anthropologists. It is crucial to all of anthropological thought. The proof of parallel development could lie in determining whether or not similar textile and metallurgical techniques, calendrical systems, art styles, etc., originated independently in Asia and America. The inescapable conclusion would be that what happened this one time could have taken place in other instances as well. The results of everything written since Ratzel and Boas in order to disprove independent parallel development would be jeopardized. We cannot base our theories on two contradictory sets of principles.
In recent years the problem has been studied systematically by comparing whole archeological complexes, circumscribed by area and date, both in the New World and in the Old. It is now known that art styles appeared in America not only in the same sequence as comparable ones in Asia, but even at approximately the same dates, and that other correspondences, such as those in calendrical and cosmological systems or in metallurgy, fit into this chronological pattern. This cannot be accidental. There were no movements of whole populations from Asia to America, nor colonial settlements like those of the Europeans after Columbus. Arguments in favor of the independent development of ancient American civilizations that were based on the absence of Old World crops and various aspects of technology are thus less compelling. Chinese records make it clear that at the periods in question ocean-going vessels were available both in eastern and southern Asia, vessels that could not have encountered greater difficulties in crossing the North Pacific than the clumsy Manila galleons of the sixteenth and seventeenth centuries. In summary, we are justified in stating that as matters stand America offers no exception to the rule according to which close similarities between complex cultural phenomena are the results of diffusion.
The historic role of diffusion
Diffusion has always had a catalytic function in sociocultural development. “The comparatively rapid growth of human culture as a whole has been due to the ability of all societies to borrow elements from other cultures and to incorporate them into their own” (Linton 1936, p. 324). Moreover, the necessity of integrating newly acquired elements into one’s cultural heritage creates new problems, which demand new solutions and thereby engender new ideas. It was the opportunity for relatively rapid interchange of inventions and ideas between a number of local cultures that made possible the birth of the oldest civilizations in the Near East. It was stimuli emanating from these oldest civilizations which started the chain reaction that eventually resulted in the emergence of one civilization after the other through the whole of world history (Heine-Geldern 1956). Obviously, the cultures of marginal peoples least exposed to diffusion, such as the Australians, Tasmanians, and Fuegians, have remained the most primitive known in modern times.
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Any society can be looked upon as forming an ordered system in which all individuals and all pieces of material equipment, including land, are component parts, linked together in a multitude of ways. Such a system may quite possibly remain in a stable state for a long period of time, in the sense that economic, social, and cultural activities are carried on over days, seasons, and years according to a fixed rhythmical pattern with an invariable structure and a stereotyped distribution of roles. Changes take place only as quantitative adjustments owing to changes in size of population.
If in a subregion of the system a hitherto unknown element is introduced, say, for example, a new technical device, a new way of allotting social roles, or a new cultural manifestation, this event constitutes a perturbation that under certain conditions may be transmitted out into the surrounding regions and propagate itself until eventually the whole system has become permeated and at the same time to some degree transformed. A permeation of this kind, either partial or total, is known as a diffusion of innovation.
In some parts of the world and in certain pre-historic or historic periods, more sweeping instances of diffusion of innovation obviously have been rather unusual occurrences. On the other hand, in present-day Western societies, diffusion of innovation is in the regular course of things, and the whole social system is oriented toward constant change.
Diffusion of innovation as a social phenomenon has been noted by scholars and other observers since antiquity, and a large amount of information on specific cases is available. More is, however, known of the results of diffusional processes than of the processes in action, for the obvious reason that processes of this kind are extremely hard to observe. Since the time of Friedrich Ratzel the traditional way of studying diffusion, from the large-scale point of view, has been to compare the spatial distribution of cultural traits by the aid of maps. As a result of research work in this tradition, a set of national atlases of folk culture has been produced in Europe, each containing a wealth of suggestive information on preindustrial cultural relationships.
In recent decades there has been a growing interest in the study of modern instances of diffusion, and scholars have increasingly taken advantage of the fuller supply of quantitative data and the possibilities of immediate observation of ongoing processes. No doubt such studies can lead to results that also throw light on how diffusion took place earlier in history. One approach toward the dif-fusion process focuses on the characteristics of the acting individual and his reactions to his immediate environment. Another approach is more concerned with the social system as a whole. In the tradition of cultural history and cultural geography various macroconcepts come into the foreground, such as growth curves, centers of innovation and centers of spread, channels of diffusion, barriers to diffusion, cultural boundaries, and regional differences in receptivity. The diffusion of innovations will be discussed in terms of these organizing concepts.
Diffusion of innovation, as seen in its systemwide context, undoubtedly tends to show a series of recurring traits. The most easily observed pattern, when statistical information is at hand, is the curve of cumulative growth (Pemberton 1936; Sorokin 1937–1941). If the number of individual adopters of innovations—or in some cases such more relevant units as villages, cities, and firms— are measured over time, an S-shaped curve normally appears. This curve shows a slow take-off stage of varying length, an intermediate stage of more rapid development, and a final stage of declining growth, which seems to approach a ceiling asymptotically. Different innovations run through this process with very different speed, and various degrees of symmetry and irregularity are noted. In particular, the initial stage may vary considerably in length.
The three stages of the growth curve can normally be shown to have recurring counterparts in the way the spatial distribution of adopters develops (Hágerstrand 1965a). In the initial stage, adopters are usually concentrated in a small cluster or a small set of clusters. In the intermediate stage, expansion likewise takes place in a pattern that indicates that a new adoption is more likely to occur in the vicinity of existing adoptions than farther away; sometimes a jump of unexpected length comes about, and with it a new center of dispersal may begin to function (Kniffen 1951a). The “neighborhood effect” creates an outward movement along a more or less sharply defined frontier (as ripples on the water), while at the same time the general density of adoption behind the frontier is continuously growing. A saturation stage may be reached in the central area of dispersal while the frontier is still advancing. Statistically, therefore, the total growth curve can be divided into a set of subcurves, showing time lags between them and also different rates of growth (Griliches 1957; Jones 1963).
The neighborhood effect, together with the total pattern of spatial growth, shows itself on many different scales. It is perhaps most clearly seen when the spreading trait concerns the rural population (Hägerstrand 1953; Griliches 1960). In such cases the diffusion tends to proceed in small steps, almost from farm to farm and from village to village. However, the extent of the neighborhood effect seems to be rather different in the United States in comparison with Europe, even for rural areas.
If the innovation under observation belongs to the modern urban scene, the process has to be viewed on a nationwide or even international scale before the same fundamental patterns of change are evident. The most important cities are usually strongly reflected in the initial stages of urban or general innovations; this means that the national capitals are usually early adopters, followed by metropolitan centers next in rank. In the following stages the neighborhood effect seems to become gradually dominating over hierarchical rank (Bowers 1937; Pemberton 1938). It must be stressed that there are still very few thoroughly analyzed cases of urban innovations; the picture just given refers to ongoing investigations and may have to be revised as information is accumulated.
Centers of innovation and diffusion
Not much is known either about the factors at work behind the appearance and persistence of centers of innovation and centers of spread. It seems to hold true that certain areas or points may function as such centers over very long periods of time, emitting wave after wave in a manner that is repetitious in the main lines even if details differ. As far as the “true” centers of innovation are concerned, it might be assumed that the cumulative principle of cultural development always is more easily at work in a few restricted areas than randomly throughout a population (Sauer 1952; Edmonson 1961). It might also be hypothesized that innovative individuals are continuously attracted to areas that seem to be able to make use of their talents. Paris as a center of fashion over a long period of time is an obvious example.
The cumulative principle of development
An innovation most often consists of a new combination of some pre-existing elements, and so it cannot come into being until these elements are at hand either as ideas or as hardware. The cumulative principle is most easily appreciated in the realm of material culture, but undoubtedly it also exists in immaterial culture. The gradual development of scientific theory is a case in point, but so also is the growing richness through time in modes of expression in the visual arts and music. Because of this principle, it did not help very much in practice that Leonardo da Vinci invented an aircraft or Charles Babbage a computer; the actual realization of these things as working innovations had to await the appearance of basic component parts before production and spread were possible. However, this combination of more basic elements into more advanced ones certainly does not take place everywhere with equal ease, and the incentive to make such combinations is also affected by spatial variables.
Choice of solution. Although a certain spectrum of simpler parts must exist and be known in order to allow a new step forward, it is by no means self-evident that more advanced tasks can be undertaken only in one way. Many solutions may be possible, and a selection may be made just randomly or because of certain conditions in a steering environment. As technological diversity increases, so also do the opportunities for choice between alternative technologies or between different permutations of technological elements.
The existence of a wide range of alternative technologies asserts itself in the various cultures, within which approximately the same basic tasks have been solved differently and with varying degrees of success. It is probably not correct to think of these alternative solutions as conscious selections from a known full set of possibilities, but rather as an unsystematic trial-and-error use of elements at hand. As seen in this perspective, a center of innovation is, then, a place or area where an unusual amount of technological elements or “building blocks”—for the time and area—are available, as well as a felt need for new combinations. It would, however, be an exaggeration to claim that very much is known about these problems.
Channels of spread
Centers of spread represent a somewhat different concept. These may be original centers of innovation, but more often they are only points where already existing innovations coming from the out-side first begin to penetrate a new region. In urban or general innovational movements, the larger cities tend to take on this function. Innovation in agriculture or industry shows various different systems of centers. In general, centers of spread remain stable over long periods of time, fulfilling a normative function for their surroundings.
Centers of spread are parts of the channels of spread. The nature of these channels is relatively well known, both through historical studies and modern quantitative analysis. Even today, when the sheer quantity of information pouring forth from the mass media may seem to make every-thing known equally well everywhere without much delay, the fact is that personal communication between pairs of individuals and direct observation are still the basic instruments for the diffusion of innovation. On second thought this is not so surprising, if one realizes that new things and ideas often look complicated to the novice and that therefore people have to be able to ask questions, take things in their hands, try them, and get a feeling for them in order to fully understand and adopt.
The exchange of information between individuals is a never-ending process; it is perhaps the most important ingredient in molding a society (or one might even say the whole human race) into one system of connected links. Everyone functions in that system as a sender, a receiver, and an amplifier. The influence that reaches an individual and the influence he can exert are both a function of his particular position in the network, a position that he is born into and subsequently can extend or change only to a certain degree. Most of the time the influences that travel through the links only reinforce the stable set of cultural traits that prevails in a particular subregion of the system; but occasionally—and today more and more often —an innovational flow will pass through and, if adopted, change the patterns of traits.
Spatial range of contacts
For most individuals, it seems that the links of personal communication are heavily restricted by distance. Few actual investigations of the spatial range of regular social contacts have been carried through. However, the few that exist indicate that among farming populations in Europe and Asia the probabilities of contact decrease at a rate steeper than the square of the distance (Hägerstrand 1953; 1965a). A minority of the population may be assumed to have wider contacts, but most of these are confined to the national area; very few have links with the international field. The reason for this is not so much the difficulty of movement as the existence of linguistic barriers. As the ability to understand and use different languages varies from country to country, so inevitably the flows of influences tend to show corresponding asymmetries.
The fact that in general the links of communication tend to be a decreasing function of distance accounts for the neighborhood effect noted in the diffusion of innovation. It also means that in any local area a growing pressure on nonadopters of an innovation builds up very quickly as the number of adopters grows. This is a process that can be simulated quantitatively and to a certain extent predicted, if the parameters of the links of social communication can be estimated (Hägerstrand 1965b).
Changes in the network
The observation that the spread of innovations from certain centers tends to follow repeatedly the same spatial course seems to indicate that the communication network has a very stable configuration over time. The frequency of contacts between areas and places remains very much the same through time, even though the individuals involved change. The structure of this network, which now can be seen only vaguely, deserves close study as to morphology and ways of change. That some change takes place is obvious. In the more developed parts of the world, the distances over which regular contacts occur is gradually increasing as the means of transportation improve. This change makes the neighborhood effect more diffuse today, in the pure spatial sense, as compared to the pattern observed in earlier times, when an innovation sometimes moved along a sharper front.
The observation that the speed of diffusion of innovation is accelerating should not be explained only in terms of spatially increasing links of communication. The growing diversification in the occupational composition of populations also has to be taken into account as an explanatory variable (Edmonson 1961). Many innovations, although important for the whole society in which they become introduced, nevertheless are of immediate concern only for a fraction of the total population. This situation may mean a very fast diffusion over a wide geographical area among those professionally engaged in the application of the innovation. At the same time the spread, in terms of the numbers of adopters, need not take place differently from a corresponding development in a larger population.
The notion of a rather stable network of communication links between individuals, and especially between populations in places and areas, makes it possible to explain the existence of cultural boundaries in at least two meaningful ways. The first and classic case is the cultural boundary that follows a barrier in the communication system, caused, for example, by physiography or gaps in the continuity of settlement. The second and more interesting case is the following. Influences that step by step move out from two different centers of spread located at a distance from each other are bound to meet along a line or zone in between. If the elements are mutually exclusive, as in religious affiliation or in the use of a certain dialect, then the flows will arrest each other. A cultural boundary will appear, remain in a fixed position, and become reinforced as long as the two competing centers retain the same position and strength (Weiss 1952).
If influences channeled through the links of social communication were the only determinants of the course of diffusion and the distribution of culture elements, then the cultural map would not be as complicated as it actually is. We also have to consider a quite different group of factors, which explain the differentials in resistance and receptivity toward innovational influences.
An aggregate of complicated circumstances causes keenness, hesitation, delay, or refusal to adopt innovations suggested by signals through the communication network. Part of the picture is, of course, the personal characteristics of individuals. Another part is the necessity for various time-consuming adjustments and preparations before an adoption can be fitted into preexisting procedures, habits, and value systems. Also, the cost involved in adoption of an innovation may slow down adoption, or the revenue expected from adoption may cause the opposite reaction (Griliches 1957; 1960).
Again, not much is known in any systematic way. One can observe, however, how resistance factors work when a spreading trait suddenly stops along a religious borderline or when the spread of a new crop dies off where soil is less suitable. A similar killing effect on the spread of new types of production has also resulted from the existence of a limitation on the market. When the market cannot absorb more, it becomes gradually more difficult for new producers to enter the business and take up the innovation; several instances of out-ward growth that came to a halt because of marketing difficulties can be cited for Europe. Cases in point that have been analyzed in some detail are the agglomeration of nursery gardens in Holstein, Germany (Briiggemann 1953) and of glass-making factories in Smaland, Sweden (Nordstrom 1962).
If a diffusional process fails to break through some area of resistance, this fact may sometimes create a shadow effect over a wider region, because the nonreceptive area does not send out a stimulus for further adoption in the way it could have if the innovation had moved straight through.
Reducing resistance to change
Diffusion of innovation is an all-important part of the economic growth in all countries but particularly so in those that need development. Thus a significant question is to find out how diffusion of innovation can be encouraged. Two methods of intervention present themselves; one refers to the pattern of communication and the other to the distribution of resistance to change.
It is probably not possible to influence the structure of communication in a society through outside action, and therefore the channels of spread must be taken as given. But knowledge about the pre-existing matrix of links would be useful, because it would make it possible to choose points of introduction of desirable innovations at the most efficient centers of spread. One method for locating such centers is to try to follow the course of some earlier innovations.
The receptivity factors are perhaps more open to moderately successful manipulation, at least as far as innovations in the economic field are concerned. It is well known that economic rewards can help to break down resistance to change. The notion of a stable and given network of social communication suggests that a response to subsidies or similar devices should be most powerful where the knowledge of the innovation is most widespread, that is, just outside the areas where it has already been adopted.
Barnett, Homer G. 1953 Innovation: The Basis of Cultural Change. New York: McGraw-Hill.
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Interpersonal influence is a term used by sociologists to refer to the role of intimate, interpersonal relations in the communication of information, influence, and innovation. Students of interpersonal influence have concerned themselves primarily with describing the ways in which networks of interpersonal communication intercept messages that originate in the mass media or elsewhere and the consequent effect on the formation of public opinion, the diffusion of innovation, and the like.
Some effort has been made to compare the workings of oral communication systems in traditional societies with the flow of interpersonal influence in modern society. These investigations have emphasized, relative to modern society, the formal situations in which influence is transmitted; the elite status, often based on ascription, which gives communicators their authority; the multiple spheres over which the same communicators exert influence; and, correlatively, the hierarchical and asymmetrical flow of such influence (Lerner 1958; Eisenstadt 1955). It follows that the flow of innovation is not very rapid in such societies and that acceptors of change are often deviant or marginal members, although the successful conversion of a formal leader is often sufficient to accomplish the conversion of an entire group (Barnett 1953, chapter 14). The rate of change is also limited by inter-group relations, since acceptance of an innovation across group boundaries is dependent on the character of social relations between the groups and on more mundane things, such as distance and physical barriers. The success of such professional advocates of change as traders, missionaries, colonial administrators, and, more recently, agents of technical assistance appears to be strongly determined by their personal relations with the target group, by their ability to understand and harness existing communications channels in an acceptable way, and by the compatibility of their message with extant values and vested interests. Alternatively, some professional agents of change have succeeded only by breaking apart the traditional structure or capturing and caring for groups of deviant souls. Altogether, though, the role of informal communication has probably been underemphasized in the study of traditional societies (Gluckman 1963).
The rise of egalitarian structures of interpersonal influence in modern societies has interested students of public opinion. Tarde (1901) went so far as to argue that conversation itself is essentially a modern phenomenon, and he described the way in which the intellectual salons of his day were able to effect changes in the art, politics, and general culture of French society. Speier (1950) has shown that the middle-class coffeehouses of seventeenth-century England were similarly influential. Contemporary equivalents of these institutions will readily suggest themselves; but the communication processes that they embody have not been much studied by sociologists [seeCreativity, article onsocial aspects].
Interpersonal influence and mass communication
Indeed, interpersonal influence seemed irrelevant at first to students of the media of mass communication. At the time empirical research on the effects of radio was begun, in the 1930s, it was widely thought that the mass media would exert a powerful and direct influence on thought and practice, the more so because society was conceived as a mass of atomized individuals alienated both from traditional institutions, such as church and guild, and from intimate contact with other people. Yet, empirical research has revealed that, at least in a democratic society, the mass media are far less potent than had been thought and, in themselves, are quite unable to effect radical changes of opinions, attitudes, and actions on subjects that “matter” (Klapper 1960). At the same time, one of the major discoveries of research on mass communications (just as it is one of the major discoveries of research on mass production) is the enduring and powerful influence of interpersonal relations, even in “mass society.” However, the role of interpersonal relations in transmitting (or retarding) the flow of influence and innovation is not the same now as it was in the past. While there are some kinds of messages that apparently travel with startling speed through interpersonal networks alone (Opie & Opie 1960), the central problem of communication and diffusion in modern society has to do with the nature of the linkages between networks of interpersonal relations, on the one hand, and the media of mass communication, on the other.
The two-step flow of communication. The discovery that “people” play a part in the mass communications process is, in a sense, a by-product of a study of the decisions made by voters during the U.S. presidential election campaign of 1940 (Lazarsfeld, Berelson, & Gaudet 1944). Employing the panel method of repeated interviews with the same people, the authors found that, despite the barrage of mass communications, there were remarkably few voters who had changed their minds during the course of the campaign. Those who did change their vote intentions, however, reported that other people, rather than the mass media, had influenced them.
An attempt was then made to locate people who had been influential on others. Study of these “opinion leaders” revealed that they had few personal or social traits that distinguished them from others. This suggested that such influence goes on in the course of everyday contacts among like-minded people who share similar characteristics. The influentials were different, however, in their greater exposure to the mass media. A “two-step flow of communication” was therefore hypothesized; the media were held to reach widely dispersed opinion leaders, who then passed on what they had learned to those for whom they were influential.
This hypothesis inspired a series of studies of the influence of different channels of communication, including interpersonal influence, on the purchase of consumer goods, the communication of political ideas, the adoption of a new drug by physicians, and the like. Taken together, these studies suggested that conversation with other people is generally more influential than the mass media in decisions to accept some new idea or practice; that people who influence others are typically close associates; that influentials “specialize,” for example, a woman who influences another in the decision to try a new food product will probably not be influential in the field of fashion; and that both partners to an influence transaction have to have a minimum level of interest in the subject before any influence is exchanged, but that the influential person is probably somewhat more interested. It also appeared that influentials are more exposed to “outside” sources, generally, but particularly to those sources—mass media, or particular institutions, or other people—that have direct bearing on their spheres of influence; that, despite this greater exposure, it is unusual even for an influential to report that one of the media of mass communication has been the major source of influence on his own decision; and that the function of interpersonal relations is not only to transmit information but to “legitimate” decisions (or to veto them), as well as to provide the kind of social support necessary for taking innovative risks (Katz 1957).
Re specification of the two-step flow hypothesis. Thus the studies mentioned above contributed to the specification of the two-step flow hypothesis by, on the one hand, exposing it as overly simple, but, on the other hand, confirming the validity of approaching the flow of influence and innovation via the interaction of mass media and interpersonal communication. As a direct result, two other things were also accomplished. First, there was effected a kind of convergence, or, at least, a growing mutual interest, among various traditions of study of the diffusion and acceptance of innovation that previously had not recognized any kinship. In particular, in departments of sociology and, to a certain extent, in schools of journalism, students of mass communication discovered, to everybody’s surprise, that they shared a set of problems with rural sociologists studying the diffusion and acceptance of new farm practices, with anthropologists studying the spread of culture and technology, and with folklorists, researchers in education, archeologists, geographers, and others (Katz, Levin, & Hamilton 1963). Second, this series of studies gradually led to the realization that the design of research on the diffusion of innovation needed revision.
The design of diffusion research
The 1940 voting study had departed from the traditional design of mass communications research in that it did not seek to locate the effect of a given message in a given population but, instead, sought to “reconstruct,” with the help of the respondent, the sources of information and influence that had gone into the making of a decision. It was this research procedure that made possible the discovery that interpersonal influence had a substantial part in the process of decision making. As the role of interpersonal influence became clearer, methods were developed for locating and studying influentials (Katz & Lazarsfeld 1955). And, gradually, the focus of research shifted from a concern with interpersonal influence as simply a channel of communication bearing on individual decisions, to a conception of interpersonal relations as networks of communication through which influence and innovation spread through society.
Diffusion, acceptance, and influence
With this conception in mind, a study was carried out of the diffusion of a new drug among physicians. This study employed the methods of sociometry to map the potential channels of interpersonal communication; in this way, it was possible to explore the extent to which the channels were actually utilized in the transmission of an innovation over time and to locate those points at which they were linked to “outside” sources of influence (Coleman, Katz, & Menzel 1957). Note that this concern with the process of “diffusion” (as distinct from a concern with the effects of mass communications or with the interlocking roles of mass media and interpersonal communication in the making of individual decisions) led also to the choice of a specific item for study (a new drug) and to a method for dating the acceptance of the item by each adopter [seeScience, article onscientific communication].
The components of the process called diffusion thus came into better focus. Diffusion could then be defined as the acceptance of some specific item, over time, by adopting units—individuals, groups, communities—that are linked both to external channels of communication and to each other by means of both a structure of social relations and a system of values, or culture. Rural sociologists studying the diffusion and acceptance of new farm practices arrived at much the same conceptions (Lionberger 1960), and it is noteworthy that the design of a study of the diffusion of hybrid seed corn (Ryan & Gross 1943) parallels, in a number of important respects, the just described, much later study.
This definition of the diffusion process makes it possible to point out some of the methodological problems in designing research on the role of inter-personal influence in diffusion and in discussing some of its findings. It is evident, first of all, that one must specify the kind of item one has selected for study. While the original formulation of the two-step flow hypothesis referred only vaguely to the flow of ideas, it is altogether clear, by now, that items of information must be distinguished from items that require changes of attitude (influence) or action (innovation). Various proposals have been made for classifying innovations in terms of such concepts as their communicability (how easily can their working be described), their pervasiveness (how many of the adopters’ roles are implicated), the amount of risk involved, and the like. The familiar distinction between “material” and “nonmaterial” items may be redefined in these terms (Menzel 1960). The important point, in the present context, is that different kinds of items are transmitted over different kinds of channels.
Second, the concept of “acceptance” must be given operational definition. Distinctions have been made between such concepts as “external conformity” and “internalized acceptance,” or between “compartmentalized acceptance” and “full fusion with previous values.” There is a noteworthy convergence here between students of acculturation and social psychologists concerned with change of opinions and attitudes (Spicer 1954; Kelman 1958). A related emphasis is to be found in recent writings in the field of rural sociology, where the process of acceptance is divided into stages, beginning with the stage of “awareness” of the innovation, and continuing through “interest,” “evaluation,” “trial,” and finally “acceptance” (Lionberger I960; Rogers 1962). While there is debate over the names and the number of stages, whether the stages are sequential in time and prerequisite to each other (thus constituting degrees, or levels, of acceptance), or whether they are simply different dimensions of decision making, which may be ordered differently or even concurrently (Mason 1964), it is now well established that the several media are differentially appropriate to different stages.
After characterizing the item selected for study, and giving an operational definition to what constitutes its acceptance, there remains the task of determining whether or not influence has taken place, and, if so, by what means. Most diffusion studies have relied on the respondent’s recall, aided by a detailed interview, of how (and perhaps when) he first heard of the item and what other sources he consulted prior to adopting it. In an attempt to obtain more valid data, other studies have preferred variations on this basic method. Thus, many studies have attempted to infer causal relationships from observed correlations between a respondent’s (usually self-reported) communications behavior and his innovative behavior. A typical finding is that farmers who have more frequent contact with the extension agent adopt new practices earlier (see, for instance, Emery & Oeser 1958). Another major set of studies is based on tracing the flow of “planted” messages, rather than relying on more nearly natural events (Dodd 1958).
Particularly problematic is the methodology of taking account of interpersonal influence within the design of the sample survey. In small communities, such as those of physicians or farmers, complete enumeration is possible; and sociometric methods can be readily adapted. To trace the spread of some new fashion in a metropolis, on the other hand, networks of interacting individuals must somehow be sampled. One way to do this is to select the usual kind of representative sample and then to build up a social “molecule” around each respondent.
Some functions of interpersonal influence
As for the functions, or the impact, of interpersonal communication, the first thing that must be said is that it is not a major source for the diffusion of noteworthy information. The function of the mass media is to provide a direct link between the public and the makers of news, the creators of fashion, or the producers of new products; inter-personal communication cannot compete with the mass media in this respect. The two-step flow hypothesis was understood as implying that opinion leaders relay information to others who are not exposed to the media, and, as a result, several studies were undertaken to prove that the vast majority of the American public learns about major news events directly from the mass media (Deutsch-mann & Danielson 1960). Interestingly, when an event is of such magnitude that early hearers run to tell others what they have heard, interpersonal channels do serve as a major source of information; the assassination of President Kennedy was such an event, and it is likely that upward of 50 per cent of the population first heard the news from other people (Greenberg 1964). Interpersonal communication may also play an informational role when an event is of importance to a small group of people, or where the mass media are under strict official control (Bauer & Gleicher 1953), or where the mass media are not yet fully accessible. Indeed, it appears that the two-step flow hypothesis, as applied to the diffusion of information, best fits developing areas, where some of those who are exposed to the mass media pass on what they have learned to “less active sections of the population,” who are otherwise unexposed and who do not relay the message further (Abu-Lughod 1963).
What is true for information about news events is also true for first information about technical innovations. Rural sociologists and others have found that the channel that makes for awareness of an innovation is typically a formal one—generally one of the mass media, or an institutionalized source such as a dealer or salesman, whose job it is to spread news of the innovation as quickly as possible to as many people as possible. But extremely few people adopt an innovation on the basis of awareness alone. At the stages of interest and evaluation, more personal sources, both formal and informal, take over; and the impersonal media become quite unimportant. The mass media “inform” decisions; interpersonal contacts “support” and “legitimate” them.
Effectiveness of interpersonal influence
Many writers have speculated about the reasons for the greater effectiveness of interpersonal influence. Interpersonal influence, it has been pointed out, is two-way communication; the audience can talk back and convince itself. It is flexible, in the sense that the communication can be adapted to the recipient’s particular situation. It is more trustworthy, because it is assumed to be motivated by the recipient’s interest rather than the personal or professional interest of the influential; one rarely gets advice not to do something from a professional agent of change, whereas friends and neighbors frequently give such advice. Interpersonal influence is typically embedded in casual conversation and is often a by-product of such conversations (which are gratifying in themselves), compared with the more “purposive” communications of formal sources of influence. Interpersonal influence is generally “local” and thus is more likely to be both instrumentally and normatively appropriate, under local community conditions; and, what is more, a local influential can be held directly accountable for his advice. By the same token, a person seeking to influence another can provide immediate reward or punishment for acceptance or the lack of it, whereas other communication media can rarely provide immediate reward or punishment.
Some of these attributes also characterize more formal and purposive interpersonal communicators, such as agricultural extension agents, salesmen, or community health workers. Or, to put the matter another way, formal sources of influence (particularly when these are also personal) may be perceived by some people as sufficiently trustworthy, sufficiently accessible, sufficiently normative (although these norms may be at odds with those of the local community), or sufficiently gratifying in themselves to motivate the acceptance of influence. This would seem to be the case for early adopters of technical innovation, in particular, but also for marginal members of a community who embrace the agent of change as a welcome companion. For most people, however, the word of a trusted friend or a respected colleague is a prerequisite to action.
Interpersonal influence and social change
It is incorrect, however, to infer from the role of interpersonal influence in the acceptance of social and technical change, whether in the field of diffusion or, say, in a field like group dynamics (Lewin 1947), that interpersonal influence is a channel that functions primarily in the service of change. Indeed, rural studies have shown that, under certain conditions, the more farmers one talks to the later one is likely to accept an innovation; and the same thing is true if one uses interpersonal channels to learn about an innovation for the first time (Wilkening, Tully, & Presser 1962; Copp, Sill, & Brown 1958). Studies of political communication have shown that while the mass media may motivate someone to change his political intentions, it is conversation that prevents the change (Deutsch-mann 1962). In fact, the mass media may be said to be most effective when interpersonal communication is inoperative for some reason, as when a topic is not sufficiently interesting or important to motivate discussion, when one finds oneself among others whom one prefers not to hear, when a topic is taboo, or when a totalitarian regime suppresses personal contacts (Klapper 1960). Otherwise, it may safely be said that the tendency of interpersonal influence is a conservative one. Since a person who is motivated by the mass media on a given subject is also more likely to discuss it with others, and since these others typically share his prior sentiments, interpersonal communication probably reduces the pace of change. Only when a communication or a proposed innovation is deemed compatible with group norms, particularly if the group has an over-all norm of “progressiveness” or “openness to change,” or when one’s consultant has already been won over, does interpersonal influence reinforce the message of change. In other words, whether interpersonal communication will result in a change of attitude or behavior depends partly on whom one talks with. But it should be borne in mind that the influential members of a group are also bound by group norms; while influentials in progressive groups have a higher rate of innovation, influentials in conservative groups lead in resisting change (Marsh & Coleman 1954).
The flow of interpersonal influence
In discussions of the flow of interpersonal influence, the central figure appears to be the natural leader or the opinion leader, in other words, the individuals to whom others look for advice. It is evident, from many studies, that such people exist; and while sociometric techniques are probably the most appropriate means for locating them, there is also some reason to believe in the validity of a self-designating technique whereby respondents are asked (in effect) whether they have recently influenced another person in some matter, or whether anyone has come to them for advice. Experience has shown that it is rare for more than 30 per cent of a population to answer such questions in the affirmative.
Characteristics of influentials
Whether influence is accepted from an influential who is precisely like the seeker, or from one who is different in some way, apparently depends on a number of factors. In modern societies, at any rate, influentials are more similar to those whom they influence and more specialized in the areas over which they are influential; influentiality is also less likely to be synonymous with the holding of formal office. The early studies of decision making in the realms of marketing, fashion, politics, and the like emphasized the fact that influentials were hardly distinguishable from those whom they influenced, at least as far as attributes of social status were concerned. Studies in the field of rural sociology have emphasized that farmers who are actively seeking information reach out beyond their own neighbor-hood and status levels to consult other farmers who are more competent than they, even though their access to the farmers they consider “best” may be limited by status disparities and clique boundaries. This behavior is characteristic of “progressive” communities, and particularly communities of professionals. Where the need for information and advice is less keenly felt, the source is likely to be found much closer to home (Blanckenburg 1964).
Competence and accessibility are not the only attributes of influential; strategic location, with respect to some relevant outside source, is another, as is the case with drivers of buses and trucks who bring news of the outside world to outlying villages in underdeveloped areas, or even up-to-the-minute market news in modern agricultural settings. This, of course, is simply a version of the two-step flow of communication that in more sophisticated guise takes the form of propositions such as the one that finds rates of diffusion in different communities related to the extent to which farmers in each community talk about farming with respected others who have more extensive contacts with the communications media than themselves (Coughenour 1964). In other words, communities in which interpersonal and mass media networks are more closely integrated are characterized by a more rapid rate of diffusion. In such communities, interpersonal networks are organized hierarchically in terms of competence and range of outside connections, although probably less so in terms of social class. The diffusion of a new fashion, to take a different example, probably proceeds through even more homogeneous channels, although this does not preclude the possibility that the chains of interpersonal contact link up, at key points, with those of a higher social class. The fact that most individuals follow the lead of their closest associates does not necessarily contradict the hypothesis (Tarde 1890) that fashion “trickles down” through society.
Chains of communication
It is important to emphasize that influentials and influences are not usually very different from each other, nor do they constitute isolated dyads. Instead, they are better conceived as part of a long chain of interpersonal connections that embraces large segments of a community, or even a nation. In fact, it is very likely that the concepts of “opinion leader” and “influential” have been overstressed—the more so because it is almost impossible to single them out as a distinguishable target audience. The more basic stress should be placed on intimate interpersonal relationships and their function as channels of communication and as anchorage points for group norms.
For instance, given an undifferentiated population, communicating freely and continually with one another, it is possible to specify mathematically the properties of the growth curve that would describe the flow of innovation. Deviations from the expected curve may result from differentiation, and thus from the restricted access of certain people to each other; or they may reflect external sources of influence (such as the mass media) impinging on the network at more than one point. Such mathematical models have long been of interest to diffusion researchers (Tarde 1890; Chapin 1928; Dodd 1958; Coleman 1964; Hagerstrand 1965). It has even been suggested that the neolithic era must have been characterized by this kind of homogeneous population and, consequently, that there was an essentially uninterrupted, world-wide spread of innovations moving at a constant rate (Edmonson 1961).
Differential activation of communication networks
It should also be noted that a social structure of interacting individuals typically includes many different networks of communication that are differentially activated by different topics. For example, the drug study referred to earlier found that the network of professional relations among physicians was particularly active early in the history of the new drug, whereas the network of friendship relations among physicians began to transmit information and influence only after the drug was better established (Coleman, Katz, & Menzel 1957). An attempt to replicate the same study in a large city suggested that only the professional network, but not the friendship network, was active; this implies that the size of a community may affect the degree of overlap and specialization, as well as the different functions, of different networks of inter-personal relations. A parallel example may be found in the fact that different social classes employ different kinds of networks for transmitting similar communication content; this is the case with lay networks of referral and advice giving in the seeking of medical help (Freidson 1961). By the same token, the culture of a community defines the differential appropriateness of different interpersonal channels for the different sorts of communication; in a traditional society, for example, channels reserved for sacred communications are violated by the transmission of secular communications (Eisenstadt 1955).
Creation of new networks. Sometimes people go outside their interpersonal networks to send or receive influence. One way of looking at revolutionary change, for example, as compared with changes in fashion or technology, is to examine the extent to which new networks are created for the transmission of influence. Each successive fashion tends to travel through the same networks, simply succeeding the fashion that came before. Revolutionary change, on the other hand, may often be characterized as both a disruption of the traditional networks in which individuals have been embedded and as the creation of new channels of communication. Another occasion on which individuals may go beyond their traditional networks of communication is during disasters or other types of major catastrophe. The death of President Kennedy, for example, found people telling the news to total strangers on the street—and discussing it with them (Greenberg 1964; Greenberg & Parker 1965). interpersonal communication to think of how much It is a good illustration of the latent functions of more than mere information was being conveyed in these conversations.
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"Diffusion." International Encyclopedia of the Social Sciences. . Encyclopedia.com. (November 20, 2017). http://www.encyclopedia.com/social-sciences/applied-and-social-sciences-magazines/diffusion
"Diffusion." International Encyclopedia of the Social Sciences. . Retrieved November 20, 2017 from Encyclopedia.com: http://www.encyclopedia.com/social-sciences/applied-and-social-sciences-magazines/diffusion
Diffusion is an important process for bodily function. Important substances, such as oxygen and carbon dioxide, not only need to diffuse within a particular fluid volume but need to diffuse from one bodily compartment to another across barriers, where generally diffusion will be slower than within a fluid. Consider the position in the lungs; oxygen from the air has to diffuse across the walls of the alveoli and of the capillaries within the lungs to reach the blood, and then across the walls of the red cells to reach the haemoglobin. Fortunately it combines with the haemoglobin to form oxyhaemoglobin, thus maintaining a steep concentration gradient. At the same time carbon dioxide, released from the venous blood, needs to diffuse in the opposite direction, down its concentration gradient, into the lungs, in order to be exhaled. As the transit time of blood in the lungs is just a few seconds, the diffusive process needs to be rapid. (If, for example, the lungs are filled with thick, viscid mucus, as in bronchiectasis or cystic fibrosis, then the diffusive process is impaired and full oxygenation will not occur). Conversely, when oxygenated blood arrives at the tissues the conditions are such that oxygen is released and needs to diffuse into the cells to maintain tissue respiration, whilst carbon dioxide, a product of tissue respiration, needs to be loaded into the blood for conveyance back to the lungs.
Diffusion is similarly important in the absorptive processes in the gut. The purpose of digestion is to break down complex molecules into simple ones such as sugars, fats, and peptides. The lining of the gut wall has many specialized transporters to take the breakdown products into the cells and to transfer them to the blood, for delivery to tissues where they can be used as a source of energy, stored, or used for growth and repair. However, to arrive at the transporters the products of digestion need to diffuse from the gut contents, through the aqueous stationary layer closest to the lining of the gut, to reach the transporters. Diffusion therefore is a universally important process affecting every aspect of living tissue. A single living cell is a hive of activity. Substances produced within the cell which are important for its normal functioning may be produced at one site but then interact with another part of the cell, which they reach by diffusion, moving from high concentration to low by way of thermal motion, an inherent physical property.
Alan W. Cuthbert
"diffusion." The Oxford Companion to the Body. . Encyclopedia.com. (November 20, 2017). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/diffusion
"diffusion." The Oxford Companion to the Body. . Retrieved November 20, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/diffusion
diffusion, in chemistry, the spontaneous migration of substances from regions where their concentration is high to regions where their concentration is low. Diffusion is important in many life processes. It occurs, for example, across the alveolar membrane of the lung, which separates the carbon-dioxide-rich blood from the oxygen-rich air. Oxygen diffuses across the membrane and becomes dissolved in the blood; carbon dioxide diffuses across the membrane into the air.
The spontaneous redistribution of a substance is due to the random motion of the molecules (or atoms or ions) of the substance. Because of the random nature of the motion of molecules, the rate of diffusion of molecules out of any region in a substance is proportional to the concentration of molecules in that region, and the rate of diffusion into the region is proportional to the concentration of molecules in the surrounding regions. Thus, while molecules continuously flow both into and out of all regions, the net flow is from regions of higher concentration to regions of lower concentration. Generally, the greater the difference in concentration, the faster the diffusion.
Since an increase in temperature represents an increase in the average molecular speed, diffusion occurs faster at higher temperatures. At any given temperature, small, light molecules (such as H2, hydrogen gas) diffuse faster than larger, more massive molecules (such as N2, nitrogen gas) because they are traveling faster, on the average (see heat; kinetic-molecular theory of gases). According to Graham's law (for Thomas Graham), the rate at which a gas diffuses is inversely proportional to the square root of the density of the gas.
Diffusion often masks gravitational effects. For example, if a relatively dense gas (such as CO2, carbon dioxide) is introduced at the bottom of a vessel containing a less dense gas (such as H2, hydrogen gas), the dense gas will diffuse upward and the less dense gas will diffuse downward. It is true, however, that at equilibrium the two gases will not be uniformly mixed. There will be some variation in the density and composition of the gas mixture; at the top of the vessel the gas mixture will be slightly less concentrated, and there will be a slight preponderance of molecules of the less dense gas. These differences, which are due to gravity, are almost impossible to measure in the laboratory, although they interact with other factors in determining the distribution of gases in planetary atmosphere.
Diffusion is not confined to gases; it can take place with matter in any state. For example, salt diffuses (dissolves) into water; water diffuses (evaporates) into the air. It is even possible for a solid to diffuse into another solid; e.g., gold will diffuse into lead, although at room temperature this diffusion is very slow. Generally, gases diffuse much faster than liquids, and liquids much faster than solids. Diffusion may take place through a semipermeable membrane, which allows some, but not all, substances to pass. In solutions, when the liquid solvent passes through the membrane but the solute (dissolved solid) is retained, the process is called osmosis. Diffusion of a solute across a membrane is called dialysis, especially when some solutes pass and others are retained.
"diffusion." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (November 20, 2017). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/diffusion
"diffusion." The Columbia Encyclopedia, 6th ed.. . Retrieved November 20, 2017 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/diffusion
Diffusion is the movement of molecules from a region of high concentration to one of low concentration. If you have ever opened a bottle of cologne or perfume, you have witnessed diffusion. Molecules of the scent escape from the container, where they are present in very high concentration. They spread outward in every direction to regions where they are in low concentration. Your nose is able to detect the smell of the cologne or perfume even if you are quite a distance from the bottle that has been opened.
Diffusion occurs in all states of matter: solid, liquid, and gas. It occurs rapidly enough to be observable in a reasonable period of time, however, only in liquids and gases.
You can demonstrate diffusion easily in your home. Fill a glass with water. Then add 10 drops of ink (any color) to the water very carefully. The ink sinks to the bottom of the glass because it is more dense than water. Place the glass in a place where it will not be disturbed and make observations of it every day. Over time, the colored ink at the bottom of the glass spreads upward. It moves from a region of high concentration to one of low concentration.
Eventually, the water in the glass is the same shade: a grey, light blue, or pink throughout. The original black, blue, or red ink has been diluted with water to produce the paler shade. Diffusion eventually stops because no region of high ink concentration remains. The concentration of ink and water is the same throughout the glass. That rule applies to all cases of diffusion. When differences in concentration no longer exist, diffusion stops.
Osmosis is diffusion through a membrane. The membrane acts as a barrier between two solutions of different concentration. One substance (usually water) travels from an area of high concentration to one of low concentration. Osmosis can be compared to the examples of diffusion given above involving perfume and ink. In those cases, no barrier was present to separate perfume from air or ink from water. Diffusion took place directly between two materials.
In contrast, a barrier is always present with osmosis. That barrier is usually called a semipermeable membrane because it allows some kinds of materials to pass through, but not others.
The most familiar example of osmosis through a semipermeable membrane may be a living cell. Cells contain semipermeable membranes
that act something like a plastic baggy holding cell contents inside. The cell membrane is not a solid material, however, but a thin sheet containing many tiny holes. (Imagine a self-sealing sandwich bag—its surface dotted with minuscule holes—then filled with water.) The holes allow small molecules and ions (such as molecules of water and sodium ions) to pass through, but trap larger molecules (such as proteins) inside the cell.
[See also Dialysis ]
"Diffusion." UXL Encyclopedia of Science. . Encyclopedia.com. (November 20, 2017). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/diffusion-1
"Diffusion." UXL Encyclopedia of Science. . Retrieved November 20, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/diffusion-1
Some diffusionists sought to prove that all human culture originated in one place and spread out from there by diffusion. The similarities between Mayan temples and Egyptian pyramids led anthropologists like W. Perry (1887–1949) and Elliot Smith (1871–1937) to argue that Egypt was the fount of human culture (see, for example, W. J. Perry , The Growth of Civilization, 1926
Anthropology has largely moved away from this debate, seeing most cultural traits in disparate areas as having developed independently, and criticizing the diffusionists for extracting cultural artefacts from their context. For example, although the Mayan temples and Egyptian pyramids share a similarity of form, they have completely different religious functions. Some of the original interests of the diffusionists have continued to be pursued by the American historical school of anthropology. See also GALTON'S PROBLEM.
"diffusion." A Dictionary of Sociology. . Encyclopedia.com. (November 20, 2017). http://www.encyclopedia.com/social-sciences/dictionaries-thesauruses-pictures-and-press-releases/diffusion
"diffusion." A Dictionary of Sociology. . Retrieved November 20, 2017 from Encyclopedia.com: http://www.encyclopedia.com/social-sciences/dictionaries-thesauruses-pictures-and-press-releases/diffusion
1. Movement of molecules or ions from a region of higher to one of lower solute concentration as a result of their random thermal movement. For example, ions diffuse through a solution or melt towards growing crystals as their incorporation into the solid phase reduces their concentration in the immediately adjacent liquid.
2. (in crystals) (a) Self diffusion involves the movement of a unit of a given composition through a crystal lattice of the same composition. (b) Volume diffusion, the movement of atoms or ions through the crystal lattice. It includes simple self diffusion and more complex situations where ions of a certain species migrate through a lattice containing a variety of ions of different sizes or charges and in various configurations. Self diffusion leads only to change in shape or texture, volume diffusion leads to changes in composition.
"diffusion." A Dictionary of Earth Sciences. . Encyclopedia.com. (November 20, 2017). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/diffusion
"diffusion." A Dictionary of Earth Sciences. . Retrieved November 20, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/diffusion
dif·fu·sion / diˈfyoōzhən/ • n. the spreading of something more widely: the diffusion of Marxist ideas. ∎ the action of spreading the light from a light source evenly so as to reduce glare and harsh shadows. ∎ Chem. the intermingling of substances by the natural movement of their particles: the rate of diffusion of a gas. ∎ Anthropol. the dissemination of elements of culture to another region or people. DERIVATIVES: dif·fu·sive / -siv/ adj. ( Chem. ).
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"diffusion." A Dictionary of Nursing. . Encyclopedia.com. (November 20, 2017). http://www.encyclopedia.com/caregiving/dictionaries-thesauruses-pictures-and-press-releases/diffusion
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"diffusion." Oxford Dictionary of Rhymes. . Encyclopedia.com. (November 20, 2017). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/diffusion
"diffusion." Oxford Dictionary of Rhymes. . Retrieved November 20, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/diffusion