Cultural Evolution and Units of Selection in Replicating Text

The use of biological models and metaphors in studies of culture has a long and checkered history. While there are many superficial similarities between biological and cultural evolution, attempts to pin down such analogies have not been wholly successful. One limiting factor may be a lack of empirical evidence that the basic assumptions of the evolutionary model are met within a cultural system. We argue that a focus on the detection and description of the units of selection is an essential first step in constructing any evolutionary model. In this paper we outline the necessary connection between units of selection and evolution, describe the properties of a unit of selection, and introduce an empirical method for the detection of putative units of selection in a model cultural system: discourse within NetNews, a discussion system on the Internet.