Science is a very special form of storytelling, one in which the stories told have to be testable against empirical observation. But the world is a complicated place; and, to provide a coherent account of it, scientists often find themselves obliged to join up their observable dots using untestable or as-yet-untested lines. This is a necessary part of constructing many valuable and predictive scientific scenarios; and it is perfectly good procedure as long as the assumptions involved are fully compatible with (...) what is known and testable. But it also means that, in formulating their ideas about how the world works, scientists must remain keenly aware not only of what is and is not assumption in those complex ideas, but of how untested elements may color their beliefs. The contributions to this volume cover many interesting examples of how assumptions have affected ideas in diverse areas of the paleosciences, both practical and theoretical, and they serve together as a salutary reminder that vigilance and a willingness to rethink are always in order. (shrink)