Introspection and preserved writings give us far more insight into the ways of past humans than we have into the ways of past dinosaurs. For that reason, I’m optimistic that we can eventually arrive at convincing explanations for these broadest patterns of human history.

Diamond contrasts the evidentiary limits of deep prehistory with the relative richness of human historical evidence. Dinosaurs leave mainly physical traces, whereas humans leave not only material remains but also self-reflective testimony—letters, chronicles, laws, and other preserved writings—plus the possibility of reconstructing motives and institutions through comparative study. The quote expresses a methodological optimism characteristic of Diamond’s “big history” approach: despite complexity and contingency, large-scale patterns in human history may be explainable in a way that is persuasive and testable, because the human record contains both external artifacts and internal accounts of thought and intention.