Earlier this week Richard H. Thaler posted a question to selected Edge contributors, asking them for their favorite examples of wrong scientific theories that were held for long periods of time. You know, little ideas like "the earth is flat."
The contributor's responses came from all different fields and thought processes, but there were a few recurring themes. One of the biggest hits was the theory that ulcers were caused by stress–this was discredited by Barry Marshall and Robin Warren, who proved that the bacteria H. pylori bring on the ulcers. Gregory Cochran explains:
One favorite is helicobacter pylori as the main cause of stomach ulcers. This was repeatedly discovered and then ignored and forgotten: doctors preferred 'stress' as the the cause, not least because it was undefinable. Medicine is particularly prone to such shared mistakes. I would say this is the case because human biology is complex, experiments are not always permitted, and MDs are not trained to be puzzle-solvers–instead, to follow authority.
Another frequent topic of disbelief among Edge responders was theism and its anti-science offshoots–in particular the belief in intelligent design, and the belief that the Earth is only a few thousand years old. Going by current political discussions in America it may seem that these issues are still under contention and shouldn't be included on the list, but I'm going to have to say differently, and agree with Milford Wolpoff:
Creationism's step sister, intelligent design, and allied beliefs have been held true for some time, even as the mountain of evidence supporting an evolutionary explanation for the history and diversity of life continues to grow. Why has this belief persisted? There are political and religious reasons, of course, but history shows than neither politics nor religion require a creationist belief in intelligent design. ...