Jefferson's protracted resistance to the concept of extinction was, to a large degree, a product of his religious beliefs. Although he embraced Enlightenment rationalism and rejected Christianity, Jefferson was, nonetheless, a very religious person. He was a theist who believed in a God of providence who guided human affairs. I suggest that Jefferson's attraction to the "completeness-of-nature" worldview was so strong that he was never able to abandon it, even in the face of strong empirical evidence that it was wrong.
One specific event that is best explained as a response to a religious calling is Jefferson's compulsion to write a long memoir about Megalonyx in 1797, at the same time he was very busy with other commitments. I suggest that Jefferson's strong belief in providence caused him to feel the hand of the Creator in the deliverance of the Megalonyx bones to Monticello. Jefferson felt a religious-patriotic calling to personally reveal the deep significance of these bones.
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