Massimo Pigliucci (the author of Nonsense on Stilts) is wondering whether the path to pseudoscience is a one-way street.
There are plenty of examples of theories starting as legitimate scientific hypotheses but then degenerating into pseudoscience as its advocates refuse to give up on the idea. Pigliucci offers cold fusion as one example.
But are there any examples of a pseudoscientific theory transforming into legitimate science? Pigliucci offers the example of herbal remedies. Commentors on the post offer continental drift and the endosymbiotic origins of eukaryotes as other possible examples.