Anthropology and many other current fields are the intellectual results of the comparative methods developed in the earlier 19th century. Theorists in such diverse fields as anatomy, linguistics, and Ethnology, making feature-by-feature comparisons of their subject matters, were beginning to suspect that similarities between animals, languages, and folkways were the result of processes or laws unknown to them then. For them, the publication of Charles Darwin's On the Origin of Species was the epiphany of everything they had begun to suspect. Darwin himself arrived at his conclusions through comparison of species he had seen in agronomy and in the wild.
What was Darwin's On The Origin of Species for theorists? (If the question is unanswerable, say "unanswerable")
epiphany