A Leopard Can't Change Its Spots

Directly Biblical. The Book of Jeremiah (13:23) poses the rhetorical question "Can the Ethiopian change his skin, or the leopard his spots?", using it to argue that people deeply set in bad habits can't simply choose to become good. The phrase entered English via the Geneva Bible of 1560, which renders the line as "Can the blacke More change his skin? or the leopard his spottes?" A near-identical phrase actually appears slightly earlier, in John Bale's 1546 religious pamphlet The First Examination of Anne Askew, though it's unclear whether Bale was drawing on an existing Latin Bible translation or whether the Geneva translators were echoing him.