The working definition of a superstition they use is "the tendency to falsely link cause to effect". They go on to include not only such things as religions and "lucky rabbit's feet" but alternative and homeopathic medical remedies as well. The capstone is trying to explain this as "evolutionary" behavior - claiming that even bacteria have "superstitions". Eventually they end up at "scientific superstition"!
It makes an interesting read, but I'm not sure that superstition is as "evolutionary" as described. It seems to me that for these behaviors to become a factor in biological evolution that they'd have to be pretty well reproducible, and hence have a real cause and effect relationship. The fake ones would be weeded out pretty quickly in this case.
Cultural evolution is another matter entirely, and I think that it's here that "superstition" joins myth as acts of remembrance and worship. And I think a plausible case could be made that with most superstitions, such as avoiding black cats crossing the road and not walking under ladders, the modern world is simply missing the context of the superstitious action.
Darwin never warned against crossing black cats, walking under ladders or stepping on cracks in the pavement, but his theory of natural selection explains why people believe in such nonsense.