The leopard cannot change his spots

The accepted figurative meaning of this is that men cannot change their characters, and just as a leopard is born spotted and will always be so, a man with a wicked nature is born wicked and will never be anything else. The more exact meaning is that, although not basically wicked, a man can become in the course of time so degraded and sung in ungodliness that there is no more changes of changing his ways than there is no more chance of changing his was than there is of a leopard’s changing his spots.

The source is Jeremiah, xiii, 23; ‘Can the Ethiopian change his skin, or the leopard his spots?’