What Would Refute the Darwinian Theory of Evolution?

Haldane's theory of evolution would be refuted by the discovery of a single fossilized rabbit in a stratum of cambrian rock. The import of such an observation would depend on what explanations were available under the given circumstances. If organisms were observed to be born with new, complex adaptations for anything there were no precursors in their parents, then darwinism’s gradual change prediction and mechanism of knowledge creation would be refuted. Facing more or less the same unsolved problem that palean darwin faced, we should have to set about finding an explanation that worked. Some people still argue that, well, perhaps it's just this thing called aam research framework