Search in an environment with an uncertain distribution of resources involves a trade-off between exploitation of past discoveries and further exploration. This extends to information foraging, where a knowledge-seeker shifts between reading in depth and studying new domains. We study this process in Charles Darwin by modeling the full-text of books listed in his chronologically-organized reading journals. We use the information-theoretic Kullback-Liebler Divergence, or relative surprise, between books for both his local (book-to-book) and global (book-to-past) reading decisions. Rather than a pattern of surprise-minimization, corresponding to a pure exploitation strategy, Darwin's behavior shifts from early exploitation to later exploration, seeking unusually high levels of cognitive surprise relative to previous eras. These shifts, detected by an unsupervised Bayesian model, correlate with major intellectual epochs of his career as identified both by traditional, qualitative scholarship and Darwin's own self-commentary. In addition to quantifying Darwin's individual-level foraging, our methods allow us to compare his consumption of texts with their publication order. We find Darwin's consumption more exploratory than the culture's production, suggesting that underneath gradual societal changes are the explorations of individual synthesis and discovery.
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