In 2009, I was invited to Indianapolis to give a public lecture on the evolution of religion. The lecture was part of a yearlong lecture series celebrating the 150th anniversary of the publication of Darwin’s On the Origin of Species. The lecture series, which sought to educate the public about the reach of the evolutionary sciences, covered topics including medicine, warfare, sex differences, diet and so forth. At the time I was one of a handful of evolutionarily trained scholars studying religion. The others must have been busy on the day the organizers had scheduled the lecture; hence I found myself in Indianapolis.

The spacious and ornate lecture hall had seating for well over a thousand people and was more appropriate for a production of Hamlet or Hamilton than a lecture by an unknown anthropologist. I am usually nervous before lectures, even lectures to a small room of undergraduates, and there were plenty of reasons to be anxious about this lecture. The hall had a blinding stage light that prevented me from actually seeing the audience (the venue was thankfully only half full) and in my blindness, I feared that while pacing, as is my wont while lecturing, I would inadvertently fall off the eight-foot-high stage. Of even greater concern though was my topic: discussing the evolution of religion, especially among lay audiences, can be treacherous territory. It is one thing to argue about Intelligent Design with the faithful; it is another matter entirely to inform those same people that evolution designed their faith.

Despite my apprehensions, the talk went well, or so I thought. I offered a historical survey of the evolutionary study of religion, beginning with Darwin’s own insights on religion through David Sloan Wilson’s Darwin’s Cathedral, which had been published a few years earlier. I then presented a few of my own studies that had shown how religions are particularly effective at generating social cohesion, which some have argued is an adaptive benefit of religion. Overall, quite innocuous stuff. Religious people are well aware that their communities are tightly bonded and cohesive; if an evolutionary anthropologist thinks that is adaptive, so be it.

Following the lecture, those who had questions were instructed to stand in line in front of a centrally located microphone. The first question, from an elderly man, began “I’ve been listening to you talk for an hour and I haven’t understood a word you’ve said.” I was stunned and my stomach felt like it had been dropkicked off the roof of a skyscraper. I am self-aware enough to know whether a lecture has been dynamic or disastrous and I knew my lecture was somewhere in the middle. Not my best effort, but it had been passable, and certainly comprehensible. The elderly man continued, “How can you talk about the evolution of religion? I am a Christian and my religion hasn’t changed for 2000 years.” I was stunned for a second time.

I muddled through a response, which was probably as incomprehensible to this man as my lecture had been. I tried to explain that his inability to perceive change in his own religion highlighted one of religion’s most extraordinary features: its ability to adapt to local socioecological conditions while adherents experience partaking in an eternally consistent and changeless tradition.

Anthropologist Roy Rappaport argues in his magnum opus, Ritual and Religion in the Making of Humanity, that religions achieve this sleight of hand through a hierarchy of religious discourse. He claims there is an inverse relationship between the material specificity of a religious claim and the durability of the claim. Religious ideas are hierarchically organized within communities and at the apex of a community’s conceptual hierarchy is what Rappaport refers to as ultimate sacred postulates, such as the Shahada, Shema, or Vandana Ti-sarana for Muslim, Jewish, and Buddhist communities respectively. Rappaport describes ultimate sacred postulates as unfalsifiable and unverifiable because they lack material specificity. They are highly resistant to change, although because of their ambiguity they may be reinterpreted anew each generation. However, below ultimate sacred postulates in the religious hierarchy are various cosmological axioms, ritual proscriptions, commandments, directives, social rules and other religious assertions that do experience varying levels of change, depending on their material specificity.

Religious rules adjust and transform all the time but such changes are understood by those who experience them as an intensification of acceptance. Religions rarely invalidate the old completely; change occurs by adding to previous practices and beliefs and elaborating upon them, while other beliefs and practices slip away unnoticed. Once sacralization is internalized, it is indeed very difficult to convince adherents that something consecrated is no longer holy. Hence, when undergoing change, religions often retain the most sacralized elements and augment them. Missionaries often retain the dates of pagan celebrations, Jewish prayers appear in the Catholic Mass, and in Micronesia, where I’ve conducted fieldwork, they have held onto their pantheon of gods and ancestral spirits by incorporating them into the Biblical myths that are now prominent in their lives.

Rappaport’s hierarchy of religious discourse also offers us a definition of religious extremism and an understanding of why it is so dangerous. Extremism occurs when low-level directives and social rules are attributed the sanctity – that is, the unquestionableness – of ultimate sacred postulates. When claims such as the sun revolves around the earth or social rules that deny women the opportunity to drive, divorce, or delve sacred texts become highly sanctified it impedes the ability of these rules to adapt to new social, political, ecological, and economic conditions. Religious systems that lose their adaptability become dangerous to the societies in which they exist, and to themselves, because they absolutize the relative. Under extremist regimes, for example, social rules about attire, food consumption, or gender roles can become more sanctified than life itself. In other words, extremism can turn the hierarchy of religious discourse upside down. Rappaport suggests that religions that oversanctify social rules are unsustainable. To survive, religions must adapt and religious extremism impedes adaptive flexibility, although we currently have little understanding of how long extremist groups can endure in spite of their tendency to ossify social rules. Tragically, even if such groups are ephemeral, many of them seem intent on destroying others as they destroy themselves.