Pseudo-archaeologists claim that revolutionary new theories abound within the garish covers of their books. Meanwhile, mainstream archaeology trundles along as usual, with archaeologists continually re-assessing their data and refining their interpretations as a result (sometimes in fundamental and radical ways). Such self-critical evolution is non-existent within the realm of the self-styled revolutionaries of pseudo-archaeology. Archaeologists evolve while the cranks just revolve. But what does it take for a change in the predominant archaeological paradigm? How much evidence is needed to reach the tipping-point where old theories become indefensible or irrelevant? What is the best way to deal with the unexpected? This page offers a few tentative suggestions. This page was originally a paper delivered at TAG in York in Dec 2007.