Why We Believe Anecdotal Evidence

Why do many people persist in believing that certain vaccinations may cause autism, despite the fact that there has never been any scientific evidence to support such a claim? Why is it that we continue to be suckers for all kinds of vague, unsubstantiated health claims for various herbs and food supplements? Michael Shermer, publisher of Skeptic magazine, thinks he’s found a reason. He hypothesizes that our willingness to believe in anecdotal evidence over objective data is hard-wired into our brains as a consequence of evolution. He argues that making a false positive error (believing that "A" leads to "B" when actually it does not) usually has no consequences – if you believe that a fruit is poisonous, choosing not to eat it only leaves you hungry. On the other hand, making a false negative error (failing to believe that "A" leads to "B" when in fact it actually does) can kill you - if you eat a poisonous fruit you may die.

What do you think? Read Mr. Shermer’s one-page opinion column in the August issue of Scientific American (“Wheatgrass Juice and Folk Medicine”, Scientific American August 2008, p. 42) and judge for yourself. This article might be a useful supplement for Chapter 1, Human Biology, 5th ed.