From Time.com: "Superstitious Americans…have gone to great lengths to secure the triple sevens as their wedding date, hoping the lucky numbers will make them lucky in love…It may well be the most popular wedding day in history."
Since the demand for weddings on this date was high, the price for 7/7/07 weddings should also have been high compared to other dates. Thus, only couples willing to pay a superstitious premium got married on 7/7/07. This could provide a great research opportunity. Are superstitious couples, for example, more likely to get divorced? Do they make as intelligent financial decisions as other couples do?
developed for functional reasons
Surely that is the common belief, that biases are the cost of heuristics? Obviously, that is what the "heuristics and biases" crowd believes.
_Felix,Great answer. Because I'm open to the possibility that some of what we more traditionally consider to be biases, such as the cognitive biases listed on wikipedia, may also have hardwired components in our brains that developed for functional reasons, and that we may also pay certain mental energy costs if we don't indulge them. I know combining hardwired & brain is messy and looks like a mixed metaphor or some such thing, but I'll stick with it since it doesn't seem to be getting in the way of our communication. The relation to the 7/7 wedding post is tangential at best.