Any process of evolution requires a mechanism of inheritance for the transmission of information across generations and the expression of phenotypes during each generation. Genetic inheritance mechanisms have been studied for over a century but mechanisms of inheritance for human cultural evolution are far less well understood. Sacred religious texts have the properties required for an inheritance system. They are replicated across generations with high fidelity and are transcribed into action every generation by the invocation and interpretation of selected passages. In this article we borrow concepts and methods from genetics and epigenetics to study the “expressed phenotypes” of six Christian churches that differ along a conservative–progressive axis. Their phenotypic differences, despite drawing upon the same sacred text, can be explained in part by differential expression of the sacred text. Since the invocation and interpretation of sacred texts are often well preserved, our methods allow the expressed phenotypes of religious groups to be studied at any time and place in history.