Luhmann explained that the theory of evolution provided a mechanism for overcoming problems of circularity in Durkheim's theory of society by isolating motivations from the mechanisms of change. .However, Luhmann's explanation left some unanswered questions concerning just exactly how the theory of evolution accomplishes this isolation. For example, how does this theory explain the mechanisms which drive the individual actions of people so that they develop into a society?

To begin with, the major mechanism for Luhmann's theory of society is differentiation. Social differentiation has normally been seen in teleological terms, particularly by Functionalists. By using a complex hierarchical approach to social structure we can visualize the kinds of social change which Luhmann brought out in a way that avoids that teleology. As a result, as Luhmann made explicit, one aspect of evolution which is critical to the development and change in complex systems is that it takes place only over a period of time. Also, in an extremely important break with the functionalist tradition, Luhmann not only recognized the role of chance in the evolution of social systems, he provided this unique description of the mechanism.

If we conceive of systems as open-systems-in-environments, structural changes have to presuppose non-coordinated events in systems and environments. Non-coordinated events are contingencies in themselves both with respect to their coincidence and their conjunctive causality. The contingent coincidence contingencies (and this is a plausible definition of chance) may lead to structural changes given the conditions stated by the theory of evolution.

Or course this represents a substantial, though necessary, change from the accepted Darwinian paradigm. The traditional mechanisms of evolution cannot account for structural change except as optimal modifications in response to environmental stress. In those terms change is adaptation, a logical, serial, series of events which mates the species and its niche into an optimum coexistence. In order that we might realize what kind of change Luhmann is mentioning, we need to examine two different kinds of serial change, a markov chain, and a random walk.

The traditional view of evolutionary change is much like a Markov chain. Each transformation is the logical outcome of an encounter between tile organism and its environment. Given a similar organism facing the same environmental forces the path will always remain identical. We can consider a Markov chain then, the generalization of serial rational change. A random walk, on the other hand represents a condition of non-rationality because the choice of outcomes is irrelevant to the rationality in the system. Each transformation can be represented by a machine the output state space of which is very large with a relatively even probability distribution. In this case the outcome of any single transformation is not predictable because the choice is ultimately determined by factors that are outside the system. The path of the ant on Simon's beach, on the other hand, represents an example of both kinds of serial change operating in tandem. Any attempt to analyze the ant's path in rational terms must end in frustration because once a system includes non-rational elements the rationality of the system becomes irrelevant.

Perhaps this will be clearer if we consider these simple points. Any transformation with an output state space greater than one and with an even (flat) probability distribution represents an element of non-rationality (This is quite different from a stochastic system where the probabilities fall into some form of a standard bell curve). This is true even though no matter which of the possible outcomes is chosen, that choice will be rationally determined. This is simply a property of flat probability distributions Returning to Luhmann's description of the role that chance plays in structural change in evolution theory, if we have a number of parallel serial processes in communication and in the same temporal sequence then the prediction of the simultaneous occurrence of two states is impossible. It is a matter of a choice from among equally probable states by two different processes each of which includes some non-rational elements.

Ecologist Edward Kormondy brought out an interesting example of this kind of change which would defy the analysis by normal evolutionary rules. They were studying a particular species of aphids called top-feeding aphids because of their habit of feeding on the top of the leaves of certain bushes. There were no aphids known or encountered that fed on the bottoms of the leaves. During the process of the study a number of aphids were found going under the leaves. Several generations later they had evolved into a new species of bottom feeding aphids (a new species is determined by their biological incompatibility with the old population, that is they could no longer mate with the top feeders). Since was no shortage of leaves and no excess population, the only reason why these aphids went to the bottom of the leaves was that they happened to wander there and some of them evidently liked it so well they stayed. This could happen only because there was enough variety in the feeding habits of the aphids that some of them could not only be successful in this new niche but actually because they preferred it to the old one. No logical argument utilizing only the known habits of top feeding aphids could predict the emergence of this new species. Population biologists of course, are not surprised by this because they have long been acquainted with the many roles that variety plays in the evolution of communities such as these. It should be a short step, then to realizing the added variety possible in human society where in addition to environmental pressures and the variety of possible outcomes due to non-rationality, you have the element of free choice, or as Luhmann put it;

But environments do not consist exclusively of various other systems. They also contain (and this is extremely important) the chance to seek or avoid relations with other systems.

We can add also, the possibility of rational choice, but not the necessity. Thus the choice of seeking or avoiding relations with other systems will include those we have been discussing. It will also include choices forced upon us, or at least influenced, by the environment. Since social structure are the sets of stable relations that emerge out of the interactions that occur between the members of a social system, such structures will be determined both by the chance encounters of non-rational choices and by the inevitable encounter of rational outcomes.

In a completely rational evolutionary system, a Markov chain, the system will tend toward the condition which is optimum for the environment it senses around it. However, Social systems exist in a sea of excess variety. The only variety that they can be aware of is that which they are dealing with directly. We need to recall that through the mechanisms of complex organization the system is in communication with only a limited portion of the total variety in the environment. Thus, the external unsensed variety amounts to a pool of possible non-rational decisions which the people who make up the system must contend with in a future that includes decisions concerning difficulties they have never before experienced.

Thus, we have two sources of internal variety, arbitrary choices among equally probable possibilities and encounters between the outcomes of separate transformations occurring over a period of time to different members of the social system. These serve as a reservoir of possible reactions to unfamiliar environmental stimuli Successful stable patterns which emerge from the interaction of these processes with the variety encountered in the systems environment serve as the source of social differentiation Without the added variety obtained through chance and non-rational choice, individual members of the system would always react to their environment through mechanisms that would tend to maintain the original structure. In other worlds a Markov chain. And, since under some kinds of environmental pressure that structure might turn out not to be viable, such a restriction would be flirting with extinction.

From these underlying mechanisms of change we can describe how differentiation emerges and changes. Society is a complex system. The lowest levels are derived from the interactions between the individuals that make up the society and their independent worldviews. Each person is an independent actor and must make all his social judgments from the viewpoint of his own personal picture of his society and the world it exists in. Since he is in communication with many of his contemporaries he is aware of what has worked for others as well as for himself He is also a product of his past and of the assumptions generally held by those he considers his family and peers. Separate stable and autonomous patterns of interaction emerge which constrain those activities of the members which the individual associates with each particular social system. This stability is derived from the individuals sense of what is "correct", or what seems to work. It is strengthened by the simultaneous concurrence of a number of members of the society.`

System differentiation, Luhmann said, is "Replication, within a system, of the difference between a system and its environment." He explains that in differentiated systems, we can find two environments, the external environment common to all subsystems and the internal environment of each. Differentiation, then, is the replication of the interface between the system and its environment in each of the subsystems. Our complex systems approach sees each subsystem as a semi-autonomous whole in itself integrating not with the environment of the total system but with a selected portion of that environment including such other subsystems as are appropriate by abstracting out that part of the total environment that has a meaningful effect on the subsystem. It can accomplish this because the outer environment itself is complex and it too can be related to according to semi-autonomous levels of activity.

If this seems confusing it is because the mechanisms which can create and sustain the kind of relations these descriptions require for their fulfilment have never been articulated. The active element in this kind of complex relation is always the individual. Each person exists in a pragmatic world of his own creation. A world evolved in the cognitive mechanisms of his brain out of the serial immediate interactions with a real world that exists outside, a world he has a limited knowledge of. Each individual is in communication with a number of other individuals. In this pragmatic world conceptions about the outer world are developed in two ways. First from the direct serial interactions between the individual and the real world, and second from the impressions he gets of the world from those he is in communication with. The temporal effects for the two processes are quite different. The serial interactions take place in a chronological time. There is a continuity with important or startling events marking off identifiable dates. Communications with others on the other hand, tend to modify conceptions in a time that may not be relevant to the calendar. Changes of conceptions through serial interactions evolve slowly. In stable societies, or for that matter in the more stable portions of any society, many generations may pass before any noticeable change takes place Emergent change through the parallel interaction of interpersonal communication will often take place dramatically.

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