The general theory of evolution is based on prerequisites that it cannot control itself, but which can be clarified with the help of systems theory. This particularly applies to the reconstruction of the distinction and coordination of the three evolutionary mechanisms of variation, selection and (re)stabilization (selective retention) (Mayr 1982). “While evolutionary theory distinguishes variation, selection, and restabilization, it also assumes stability (the state of being restabilized) with the idea of Variation.(1) In addition, it builds this distinction into a systems theory, presupposing that a distinction to a system’s environment can only be distinguished with a system” (Luhmann 2013a, 151). To clarify: differentiation does not mean isolating separation, according to which the distinguished elements have nothing to do with each other. Differentiation, on the contrary, means that the distinguished components reciprocally refer to each other. Differentiation, as an interruption of interdependence, is the enabling foundation for interaction. (2) “Systems theory begins with the unity of the difference between system and environment. The environment is a constitutive feature of this difference, thus it is no less important for the system than the system itself” (Luhmann 1995c, 212). The study of religion reconstructs the religious system by focussing it in difference to other objects. The religious system as the object of the study of religion empirically constitutes itself via the difference system/environment and therefore gains identity, based on which it becomes identifiable. It is, therefore, a question of the difference from a difference.

Based on second-order cybernetics, the newer systems theory highlights that for each system there is a non-specific environment, within which only noise prevails for the system, as well as a system-specific environment. With respect to meaning-constituting systems (Sinnsysteme, i. e., psychic and social systems) this means: “An environment functioning for a system is […] necessarily a two-part reconstruction of the environment itself, it is horizon and transcendence, expectation and disappointment, selection and risk, order and disorder. It is only on this basis that an interest in the environment can develop, that there can be attempts at influence and correction be given, and learning processes evolve” (Luhmann 1982, 16). Moreover, the systemic difference consists of the unity of the distinction between self-reference and other-reference so that the difference of system/environment occurs twice: “as difference produced through the system and as difference observed in the system” (Luhmann 2012, 19). As a result, a double input-output-process occurs, which can be modeled as follows (Figure 1):

A system constitutes and reproduces itself as a system-environment-difference through output 1 (externalization), which the system processor 1 initiates from. In systems theory, this process is called autopoiesis (Maturana and Varela 1980). In terms of the reconstruction of religion this means: Religion evolves and reproduces from religion itself—and from nothing else. From a system-theoretical point of view, religion is thus a sui generis issue, without turning to anything else than a socio-cultural issue based on historical development. (3)

Apart from the first processor, the system requires a second one, because: “[…] self-reference on the level of basal processes is possible only if at least two processing units that operate with information are present and if they can relate to each other and thereby to themselves” (Luhmann 1995c, 138). By means of the second processor, which enables selection, the system draws energy from either the system-specific, or, mediated by the system-specific environment, from the unspecific environment in the form of input 1 and transfers it, whilst possibly filtering noise, via input 2 into system-specific information. (4) This process corresponds to Gregory Bateson’s understanding of information as “a difference which makes a difference” (Bateson 1987, 276, 321 et pass.). Eventually, the system produces a new output. This output is partially released as output 2 into the environment, i. e. is not processed further by the system. Otherwise, the output generates the starting point for the reproduction of the system-internal difference between the system and environment in the form of output 1. Input 1 and output 2 are localized at the crossover between the unspecific and the system-specific environment. (5)

The religious system, too, has a system-specific and a non-specific environment. Anything that religion observes as non-religious but interprets in a religious way is a part of the system-specific environment; i. e. religion projects its own pattern onto the environment and then selectively takes the environment into the system, for instance, as cosmological and/or social disorder, as ‘false’ cognitions (disbelief, superstition, atheism, magic, folk religion, etc.), or considered ethically as behavior deviating from divine commandment and prohibition, (6) but also as a legitimation of the status quo, or as with dignity provided freedom of the observed environment. In ancient societies, the distinction between the religious system and the system-specific environment was sacred/profane; a distinction which is comparatively strongly tied to the physically semioticized space. (7) This restricts the possibility of variation of religious communication, but, on the other hand, makes answering the social question of where religious communication can be carried out easier, and therefore increases the chance of follow-on operations: Physical places including their objects (buildings, squares, ritual objects) are provided with religious meaning and function as a “material anchor” (Hutchins 2005) for religious communication. The evolutionary distinction of transcendent/immanent increases the spectrum of variation based on rising deterritorialization. From here, the development of religious-semantic spaces which tend to be independent of physical space, but make metaphorical reference to it, as well as renewed material embodiment and territorial relocation, is possible (Glei and Jaspert 2016). In the functionally differentiated society, the distinction between the religious system and its system-specific environment is religious/secular; however, this distinction may sometimes considerably vary semantically (Burchardt, Wohlrab-Sahr, and Middell 2015). The distinction religious/secular regulates the relationship between religion and other social subsystems such as politics, economy, law, science, education, arts, health, or social aid. It only makes sense to speak of, for example, secular law or secular science, if law and science are to be distinguished from religion, but thereby still are related to religion, or, conversely, if religion refers—positively or negatively—to law and science. The three pairs of distinctions (sacred/profane, transcendent/immanent, and religious/secular) are in a relation partially to a historical process (in the sense of overlapping, and not replacement!) and partially in an epistemic relation. Due to the historical occurrence of the respective following distinction, the respective preliminary distinction comes into (reinforced) reflection (Schulze 2015, 124–147). The reconstruction of the distinctions transcendent/immanent and sacred/profane starts with today’s distinction of religious/secular and proceeds by unfolding the evolutionary layers that have been formed earlier, but which are still in force today. (8)

Religion has no relation to the unspecific environment. The unspecific environment of every system “contains no information. The environment is as it is” (Foerster 1984, 263). The non-specific environment can only come into question from an outside observation, for instance, in the study of religion. It is an empirical question of concrete historical research to determine what belongs to the system-specific and what to the non-specific environment of religion. There are two relevant criteria for the scientific consideration of the unspecific environment within the study of religion: as environmental conditions (being possibly ecological, physiological, and psychological substrates of religion), and as a take-off for the emergence of religion. The unspecific environment is only relevant for scientific research on religion if the emergence of religion can be reconstructed by means of respective observations. For the description of the varying, selective and (re)stabilizing proceeding of religion itself, the unspecific environment is of no relevance. The difference between unspecific and system-specific environment of religion is relevant for the discussion about the question whether religion adopts to its environment or is to be understood as an evolutionary by-product. For example, those communicatively addressed religious experiences, which have certain neurophysiological and corresponding behavioral patterns as environmental correlates, can prove themselves during evolution. However, correlation does not necessarily only mean adaption (Bulbulia 2004a⁠ , 2004b ; Alcorta and Sosis 2005 ; Sanderson 2008⁠ ; McNamara 2009, 248⁠ ; Sosis 2009⁠ ; Rossano 2010, 151⁠ ; Heimola 2013), but also at least selection, which ex-post turns out to be successful and therefore is an evolutionary by-product (Kirkpatrick 1999 , 2006 ; Boyer 2003⁠ ; Atran and Norenzayan 2004 ; Pyysiäinen and Hauser 2010 ; Norenzayan et al. 2016). But even if religion is understood as an adaptation to the environment, its autonomy in the form of religious concepts, experiences and practices must be subject to the basis on which it can adapt to its environment (Kunz 2009). In order to avoid unilateral causality assumptions, it makes sense to distinguish between adaptive religious elements and religious elements as accidental evolutionary by-products and to reckon with both possibilities (Voland 2009). (9) Advantages of the selection of religiously coded experiences in connection with general socio-cultural and psychic evolution are often scientifically seen in the fact that religion is based on the release of endorphins(Dunbar, Barrett, and Lycett 2005, 166) and the messenger dopamine (Previc 2006; Wilson 2014, 89), or by means of specific ethological and psychological-cognitive patterns such as group adherence(Sosis and Kiper 2014), providing an especially pertinent reference to the physiological, psychic and social environment. However, in their own right, physiological, and psychological processes of this kind are not necessarily concerned with religiously determined experiences and communicatively ascribed behavioral patterns, and the mentioned process only explain extra-religious factors and consequences. A pronounced religiosity may also display high statistical correlations with fertility rates (Frejka and Westoff 2008⁠; Weeden, Cohen, and Kenrick 2008; Zhang 2008; Blume 2009). But this connection is only then part of religious evolution if the social form of the family, of parenthood and offspring, is attributed a specific religious sense—be it related to humans or with regard to gods and goddesses (regarding Christian religion, cf., for example, Böhm et al. 1995; Jacobs 1999;Jacobs and Krawiec 2003; Albrecht and Feldmeier 2014;Reynolds and Witte, Jr. 2007; religious-historically spanning:Nielsen 1922, 68–144; Browning, Green, and Witte, Jr. 2006;Nissinen and Uro 2008). The same applies for determined correlations between religion and subjective well-being (Witter et al. 1985; Emmons 1999; Joshi, Kumari, and Jain 2008; Baker 2011), mental health (Hackney and Sanders 2003; Gilbert 2011), the feeling of happiness (Ferriss 2002), group solidarity (Voland 2009, 15), and cooperation (Bulbulia and Frean 2010⁠; Norenzayan 2013)—especially under the conditions of subsistence economy (Peoples and Marlowe 2012). This may all be of use for the environment of religion. However, a particularly efficient form of coping with undetermined contingency based on the code transcendent/immanent is the distinct feature of religion within socio-cultural evolution, differentiated from other societal processes that cope with contingency determined respectively, for instance through law, technology, and insurance. The religious coping of undetermined contingency may include family, well-being, health, group solidarity, cooperation, as well as other elements, by means of analogies and providing these topics with specific religious meaning. Only if this happens, can factors such as those mentioned belong to religious evolution. From there, religion can serve as a component of socio-cultural evolutionary performances for other societal subsystems and social forms as well as psychic systems in the form of offering sense and realize the societal function of coping with undetermined contingency, in difference to determined contingency that other societal subsystems deal with (e. g., by means of law, technology, and insurance).

The distinction between unspecific and system-specific environment correlates with the distinction between system-environment-relations and system-system-relations. “Reference to the ‘environment’ contributes nothing to system operations. ‘The environment’ gives no information. It is only an empty correlate of self-reference. If we are dealing with system-system relations, however, indicatable entities do occur in the environment. In this case, too, the system cannot cross its boundaries operationally (if it did it would have to operate in the environment), but it can observe, that is to say indicate what specific states of affairs in the environment (other systems) are specifically relevant for it. In the relationship between system and environment, the system operates universalistically, in the form of a crosssection of the world. In relations between systems, it operates specifically, in certain, contingent modes of observation” (Luhmann 2013b, 10). The transition between the unspecific and the system-specific environment of religion is mediated via other systems. For each system, as mentioned, a specific environment exists. Economics, for instance, observes its specific environment based on the system-internal distinction paying/not paying. This distinction, in principle, belongs to the unspecific environment of religion, but may also become relevant for religion, if relations between religion and economy are taken into consideration. In this case, economic processes get into the system-specific environment of religion and can be encoded system-specifically, for instance, by observing usury as sinful and therefore prohibiting interest, (10) or conversely, viewing profit as a sign of divine election(Weber [1930] 1992).

The output released into the environment by the religious system may be ignored, rejected, or accepted as an offer of sense by other societal subsystems and psychic systems through transferring the noise into respective system-specific information. The religious system, however, has no direct influence on either its specific or, above all, its unspecific environment. The specific environment of the religious system is relevant to the study of religion, if the religious system refers to it, namely only then, if the religious system operates other-referentially with regard to other societal subsystems (for example, as political religion) and psychic systems (such as person-related religion with self-disciplining impacts or in the form of subjectification).

Religion, as a societal subsystem, has three system references: The relation of the religious system to the comprehensive societal system (function), the relation to other societal subsystems (performance; German: Leistung), and the relation to itself (reflection) (Luhmann 1982, esp. 56) (Figure 2). There is no hierarchy of any of the three system references over the others. In a functionally differentiated society, every societal subsystem—including religion—has to consider all of them synchronically. Otherwise, it would collapse.

The acceptance or rejection of performance and function belong to the specific environment of the religious system. They are other-referentially observed by religion and may be taken into reflective consideration. The system itself also consists of three levels (Salthe 1985), which in literature are labelled differently, such as “the level of interest” (the system), “the level without” (the system environment) and “the level within” (the components of the system) (Patten 1975), or as the “composition” of the system, its “environment” and its “structure”(Bunge 1979). From those three system levels, the three references, according to Niklas Luhmann, are the self-reference, the other-reference, and the system reference. But how can the differentiation of religion be understood? This question can be approached from an evolutionary theory perspective, which is the topic of the following chapter.