In 2005, a Stanford professor, John Ioannidis, published a paper called Why Most Published Research Findings Are False, and one of the things it showed was that about 80 percent of small, non-randomized studies are later proven to be wrong. read more
Needless to say there have been a lot of theories discarded along the way. The following represents my best efforts to select the 10 most spectacularly wrong scientific theories. To qualify for the list, a large number of scientists at any given time must have subscribed to the particular theory before it was eventually discarded. read more
How it was Proven Wrong: It was only with the adoption of the scientific method that many of the classical theories like spontaneous generation began to be tested. Once they were, they quickly crumbled. read more