Why Do Older Books Survive (Sometimes)? Modelling the Time Distribution of Manuscripts with a Birth-Death Approach

Understanding the survival of ancient manuscripts dating back to different periods and centuries is crucial for gathering insights into historical textual traditions and, more generally, cultural history. Previous studies have modelled the transmission of texts, particularly in manuscript form, as a birth-death process, in which the existing manuscript witnesses of a given text are simultaneously being copied and destroyed at given rates. However, these models have not fully accounted for key properties observed in real historical written traditions, such as the temporal distribution of surviving manuscripts and the heavy-tailed distribution of surviving witnesses by text. In this study, we refine the birth-death process to better explain these dynamics. We investigate the role of extrinsic historical factors on the transmission of texts, through the use of variable copy and destruction rates to reflect extrinsic historical factors, such as fluctuations in the book market or disruptions like wars. Additionally, we look into the effect of intrinsic features of the book themselves and the uses for which they were designed, be it to be stored on a library shelf or to be intensively used and copied. We test those refinements against empirical data collected for medieval traditions. Preliminary results indicate that these enhancements allow us to establish variations in production and destruction rates that align with known macro-level historical dynamics. This revised approach helps explain why we do in fact preserve (some) of the older manuscripts, and not only their most recent descendants, offering a more comprehensive understanding of manuscript survival.