How can conservative and progressive Christian denominations churches be so different from each other, despite sharing the same sacred text? For the same reason, that skin and liver cells can be so different, despite sharing the same DNA.

A common critique leveled against a religion such as Christianity is that it can be used to justify anything, from forgiveness and altruism to intolerance and aggression. The implicit assumption is that if Christians had more integrity, they would be more consistent in their behavior, such as always turning the other cheek and practicing the Golden Rule.

As soon as we begin thinking about religion from an evolutionary perspective, this critique is revealed as silly and wrong-headed. No organism is programmed by its genes to “do X”. Even bacteria have been programmed by their genes to “do X in situation 1; do Y in situation 2…”; in other words, to be behaviorally flexible (also called phenotypic plasticity).

The same point can be made for the process of development. Virtually all of the cells in your body share the same DNA, yet they are very different from each other—your skin cells, your liver cells, and so on. How is this possible? Because each specialized cell type expresses only a subset of the genes shared by all cells. The branch of biology that studies patterns of gene expression is called epigenetics.

By now it has been shown beyond a shadow of a doubt that most enduring religions are not mindless superstitions but sophisticated systems of belief and practice that adapt human groups to their environments. This is how Emile Durkheim portrayed them over a century ago, but it has taken until now for it to become a scientific consensus.1,2 Since modern religions are a product of cultural evolution (built upon a psychological foundation provided by gene-culture co-evolution), there must be mechanisms of cultural inheritance and expression that are functionally equivalent to genetics and epigenetics.

In a recent study published in the journal Religion, Brain, and Behavior, we took this seriously by comparing sacred texts to genomes and the invocation of selected passages to gene expression.3 Beginning with the first comparison, sacred texts bear an intriguing resemblance to genomes. Both are replicated with a high fidelity and even have a hierarchical and segmented structure. The Protestant Christian Bible, for example, is segmented into 66 books, which in turn are divided into chapters and verses.

For a sacred text to influence behavior, it must be invoked in some sense. Passages must be brought to mind and interpreted in a way that relates to the current circumstances of the community of religious believers.

This is what happens during every Sunday sermon, but approaching it more explicitly from a cultural evolutionary perspective can add considerable insight. Accordingly, we explored how Protestant Christian congregations with diametrically opposed beliefs use their shared sacred text. We needed an unambiguous binary trait to simplify analysis so we chose same-sex marriage as a polarizing issue. We selected three conservative and three progressive churches that were clearly divided on this subject. This included one progressive and one conservative United Methodist church, one progressive and one conservative Baptist church, one progressive Congregationalist church, and one conservative Evangelical church. The progressive and conservative UMC churches were located within ten miles of each other in the same small city in upstate New York.

We collected as many sermons from each of these churches as we could find, regardless of what those sermons were about, and counted which books of the Bible each sermon cited. Just as differences in gene expression are often visualized in the form of “heat maps” (the brighter the color, the more the gene is being expressed), we can create a heat map for the expression of books in the bible by the six churches. The results show a clear “family resemblance” between the three conservative churches (top) and the three progressive churches (bottom), which can be quantified and shown to be highly statistically different from each other.

Pronounced differences also existed at the level of chapters within books and verses within chapters. All things considered, there was very little overlap in the sections of the Bible invoked by the conservative and progressive churches, and this difference was much stronger than denominational differences. For example, the conservative UMC church was more similar to the conservative Baptist and Evangelical churches in other states than the progressive UMC church less than ten miles away in the same city.

Invoking a given passage is only half the story of biblical expression. The other half is how the passage is interpreted. To examine differences in interpretation, we compared the texts from sermons that discussed one of the few verses that were frequently cited by both conservative and liberal churches-- John 3:16 (“For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life”). The progressive churches tended to interpret this passage as signifying God’s unconditional love, but the conservative churches tended to provide other interpretations. One went so far as to say that when this passage is interpreted in the context of other passages, it shows that God does not love everyone equally or even at all. When the text from sermons interpreting John 3:16 was run through a word analysis program 4, conservative pastors used a significantly higher frequency of words connoting anger.

With our colleague, Taylor Lange, we conducted a similar analysis on another polarizing issue, stewardship vs. exploitation of the earth. We documented similar night-and-day patterns of biblical expression and interpretation to justify the different behavioral prescriptions.

Thus, when differences in Biblical citations are combined with differences in interpretation, the concept of a sacred text as a cultural epigenetic inheritance system, capable of adapting a religious community to a wide range of environmental circumstances, has much to recommend it.

While our study is modest and best regarded as a proof of concept, it can easily be scaled up and expanded in a number of directions. Biblical citations and exegesis are well preserved in the historical record, which means that the “expressed phenotype” of a religion with a formalized sacred text can potentially be measured at any time or place in history, including a fine-grained analysis of contemporary events, such as the response of Christian churches to 9/11 or radicalized Islamic movements.

Formalized sacred texts such as the Bible or Quran are the cultural equivalent of an epigenetic system because only the expression of the passages, and not the passages themselves, are allowed to change. However, the cultural equivalent of genetic evolution (the addition and subtraction of the passages) took place at an earlier stage of their history and to some extent still, to the extent that religions accumulate supplemental texts in addition to their core text. During the Protestant Reformation, even the core text of the Catholic and Orthodox Christian Bibles was reduced.

While the sacred texts of organized religions are exceptionally amenable to this kind of analysis, all human cultures have something that is equivalent: an inventory of myths, parables, proverbs, and commandments that are transmitted with relatively high fidelity across generations, which are selectively invoked and interpreted to motivate appropriate behavior in specific environmental circumstances. The elements of a cultural genome need not be regarded as sacred; often it is enough merely to be apropos, as when proverbs are invoked in modern life. Why some elements come to be regarded as sacred, in either a religious or a secular context (such as a Constitution or legal code), is an important area of future inquiry.

Returning to the common critique that “anything can be justified by the Bible”, once we see this as an asset for a cultural epigenetic system, we can reach a conclusion that is more constructive than blaming religious believers for being hypocritical. If we want religious groups to behave peaceably toward other groups, we need to provide environmental conditions that favor cooperative social strategies over aggressive social strategies. If we can accomplish that goal, then all groups with flexible cultural epigenetic systems—not just religious groups—will experience peace on earth and goodwill to all humans.


  1. Wilson, D. S., Hartberg, Y., MacDonald, I., Lanman, J. A., & Whitehouse, H. (2016). The nature of religious diversity: a cultural ecosystem approach. Religion, Brain & Behavior, 1–20.
  2. Sosis, R., Schjoedt, U., Bulbulia, J., & Wildman, W. J. (2017). Wilson’s 15-year-old cathedral. Religion, Brain & Behavior, 7(May), 95–97.
  3. Hartberg, Y. M., & Wilson, D. S. (2016). Sacred text as cultural genome: an inheritance mechanism and method for studying cultural evolution. Religion, Brain & Behavior, 1–13.
  4. Pennebaker, J. W., Francis, M. E., & Booth, R. J. (2001). Linguistic Inquiry and Word Count: LIWC 2001. Mahway, NJ: Erlbaum.