While systems theory—as was shown in the previous chapter—may clarify some conditions of the theory of evolution, evolutionary theory is able to describe how systems evolve from their environment and integrate parts of their environment. In principle, it needs to be emphasized that evolution is, strictly speaking, not a process. The evolution of religion can be described as a process, however, only with hindsight, in the sense that later conditions are prerequisites for earlier ones in scientific reconstruction—in contrast to pure chronology, but according to a retrospective genealogy. “Yet there is little scientific benefit from that. The idea of process may be suitable as a framing idea for narratives, yet all attempts have failed to determine precisely how such a process is structured” (Luhmann 2013a, 159). This applies for attempts to determine developments via natural laws, as well as for phase models and (new) dialectic developmental theories. The theory of evolution, too, is occasionally understood as a process theory—but in a misleading way. Seen from a logical perspective, the differentiation of the three evolutionary mechanisms of variation, selection and (re)stabilization (selective retention) is a circular structure: First, the term variation already presumes stabilization (what should something vary from, if not from something stable [= as identity] prerequisites?). Second, the differentiation of the three mechanisms itself is the result of evolution. “The task of theory is to clarify unplanned structural changes, and thereby the ‘morphogenetic’ construction of complex systems (or with Darwin, the diversification of species). […] Every treatment of morphogenetic questions in evolutionary theory has to pay particular attention to how forms of variation and forms of selection are separated. That is the special hallmark of evolutionary theories today—and not, for instance, periodizations concerned with progress” (Luhmann 2013a, 152.182). As for the space-time continuum, both the expansion of structural complexity and the structural changes must be taken into consideration.

The theory of religious evolution is neither a simple copy of nor a successor to the theory of socio-cultural evolution, because variation, selection and (re)stabilization (retention) of religion always proceed within the evolving and self-reproducing religious system. Nor is socio-cultural evolution identical to biological evolution (Winter 1984; Campbell 1965; Lumsden and Wilson 1985; Richerson and Boyd 2005, 191–236). The different kinds of evolution are related to each other in a metaphorical way (Maasen, Mendelsohn, and Weingart 1995). The metaphorical relation allows the comparison regarding equal/unequal. The possibility to apply elements of biological theory of evolution to the theory of societal evolution is based on a isomorphism between organic evolution and socio-cultural co-evolution, and equally, religious evolution is isomorphic towards socio-cultural evolution. (1) A isomorphism between the different kinds of evolution is given, if evolution is conceptualized as “the accumulation of changes in the organization of successive systems, caused by the differential survival of replicating units of information”(Winter 1984, 68). To adequately transfer elements of the general theory of evolution to the evolutionary theory of religion, the differentiation between the evolutionary dimensions of the physical, organic, mental, and social as well as within the social the societal internal differentiation—amongst others differentiating religion—must be taken into consideration. The social possesses an emergent eigenstate compared to mental processes (Lohse 2011)—as it is the case with consciousness (2) compared to other mutually coordinated neurophysiological processes as its environmental correlate (3), and between organic compared to physical processes (Kauffman 1995, X). (4) The eigenstate of each evolutionary dimension means that interdependence is interrupted.

A theory of religious evolution, which is held in the perspective of a sociologically focused study of religion, must take its starting point with societal evolution. In this perspective, religion differentiates itself from society and becomes a societal subsystem, without turning into anything other than a socio-cultural issue. From there, religion receives an outstanding societal significance. (5) The take-off of societal evolution consists of the externalization of natural (physical, chemical as well as organic) and mental processes to then system-internally designate them other-referentially and process the respective information self-referentially. The societal syntax is based on the semiotic differentiation of signification, signifier, and signified, because: “Societies would never have gotten under way if people had not learned to distinguish between words (self-reference) and things (other-reference)” (Luhmann 2013a, 21). Among other societal subsystems, religion differentiates itself from societal processes. This differentiation is only possible based on the general theory of evolution, which is structured, among others, through the following distinctions:

Only if these distinctions—among others—are taken into account within the theory of religious evolution, it can be understood why and how religion refers to them in its own semantics (for instance, as dualism, holism, attempt to overcome those distinctions, etc.).

Social differentiation establishes via topic-based, situational, and institutional differentiation as well as—regarding societal structure—via segmental, stratificational and, eventually, functional differentiation. For these kinds of differentiation, too, it is true that, from a historical point of view, they are not to be understood as an altering sequence, but rather as layers overlapping each other (6), and that, from an epistemic perspective, the respective previous ways of differentiation through the succeeding arrive at (reinforced) reflection. The reconstruction of the previous kinds of differentiation must, therefore, have their starting point in today’s functional differentiation and proceeds by exposing the evolutionary early forms of differentiation, which are still in force under the conditions of functional differentiation.

Taking the autopoiesis of societal evolution into consideration, i. e. the issue that society only evolves from society and reproduces only from society, “[n]either preexisting fundamental human needs nor social functions are therefore useful starting points for evolutionary explanations” (Luhmann 2013a, 154). Human needs and social functions are instead relevant for the connectivity of new developments and thus for problems of evolutionary stabilization. The same applies to religious evolution. In the perspective of functional differentiation, religion has indeed a societal function, but this does not apply to the same extent for its genesis and not at all for its evolving self-description. Furthermore, it seems reasonable for religion, under the conditions of attribution towards persons as correlates of functional differentiation, to react to mental needs other-referentially. But this does not apply to the same extent for historical development and explains even under modern conditions nothing, or if at all, only indirectly something about religion's other-referential conditions of performance.

The theory of religious evolution draws on the three evolutionary mechanisms of variation, selection, and (re)stabilization. However, in difference to the biological usage of the theory of evolution, its application in the study of religion refers variation to religious operations (i. e. particular communication), selection to religious structures (expectations, regularities, standardizations, etc.), and restabilization to the relation between the religious system and its environment. Operations, structures, and systems cannot, of course, occur independently from each other (therefore the theory of evolution is necessarily circular). But Evolution proceeds based on the differentiation of the three mechanisms. The formation of the religion-specific code transcendent/immanent and the selections within the religious system, based on this code, can only be understood if the differentiation of the evolutionary mechanisms of variation, selection and stabilization are taken into consideration. Operations are always a matter of communication; they are events that have no duration. Variation can only be the matter, if communication is registered as unexpected and/or divergent. This is usually (as already at the early stage of societal evolution) ascribed to the situation and remains without consequences. In the case that variations indicate structural patterns, which diverge from the usual, the question of positive or negative selection will be raised. Topics can then be framed by religious meaning or fall out of that framework, if other interpretations are communicated successfully. (7)

Religion co-evolves with societal evolution, which in turn is a co-evolution to psychic, organic, and physical evolution. Religion is not—however: metaphysically, ontologically, or epistemically—a priori given, as religion unfolds from societal evolution. Yet it is a socio-cultural reality sui generis, i. e. it cannot be traced to anything than itself in its emergence, reproduction, and further development, as it is also the case with other societal subsystems. (8) Consequently, it is the task of the theory of religious evolution to describe religion in both its autonomy and as a societal function.