Hamilton, Marcus J.; Briggs Buchanan and Robert S. Walker

North America was initially colonized by humans during the late Pleistocene, and over the course of the Holocene material culture diversified as local populations adapted to regional environments. However, to date, while anthropologists and archaeologists have long been interested in diversity, little is known of the process of diversification over space and time. Here, we focus on the diversification of the archaeological record of western North America over 13,000 years. By compiling time series of projectile point types and their spatial distribution, we quantify the empirical record of diversification in this region. Our results show that projectile point diversity increases exponentially over time, consistent with a simple evolutionary branching process. The spatial extent of projectile points decreases exponentially over time at a similar rate. Therefore, the evolutionary diversification of projectile point types in western North America is a fractal-like space-filling process, likely reflecting increasingly localized adaptations to regional environments and a consequent reduction in the spatial extent of cultural networks.