I started populating a list today, a list of practices in Judaism that share something in common. While many practices are biblically ordained and many are rabbinic expansions, innovations or such, there is another category: practices created specifically to deal with an already emerged problem. I am being careful about using the English word "practices." Some of these are rules, some traditions, some something else. Here is my list:
1. Kitniyot -- the prohibition against eating legumes on Passover. Because of concerns regarding certain agricultural confusion, legumes were forbidden in some communities.
2. Saying Sh'ma in the beginning of prayers each morning -- when a Persian king outlawed the saying, and sent spies to check, the spies arrived later, when the prayer was usually said. So the sages incorporated it earlier, before the spies arrived. This also accounts for the saying later in prayers on the sabbath.
3. Kiddush in synagogue on Friday nights -- guests were staying in the synagogue and needed someone to say the blessing over the wine on their behalf so it was added then for the service leader to say.
4. Baruch hashem l'olam during weekday evening services and Me'ein sheva on Friday night -- to stretch prayers so latecomers would not have to walk back from the fields alone, these prayers were added.
5. The haftarah -- when reading from the 5 books of Moses was outlawed, related sections from the prophets were read instead.
6. Repetition of the Amidah -- as many (some? most?) people couldn't read the prayers, having a prayer leader repeat the text out loud exempted those people who could not do so on their own
7. Mayim megulim -- because of the possibility of snakes' crawling into water and leaving venom behind, water uncovered overnight was not allowed
8. Second day of Yom Tov -- the confusion over the date was solved by having communities outside of Israel celebrate 2 days.
The thing is, in (I think) all of these cases, the societal pressures which drove the sages to innovate the changes/additions/limitations were resolved. The Persian king died. The agricultural confusion between grains was resolved. We no longer pray in fields in dangerous areas. We can read the Torah. The calendar was set so we know when holidays fall. In most of these cases, though, the practices have remained. [Note, I am not discussing Yayin nesech, wine used for idolatry, even though there is an opinion that the non-Jewish worship of today is not identical with the types that counted as Avodah Zarah so the concern that shaking or spilling wine would be a form of worship has been obviated]. The only ones of the examples above that I have heard are no longer normative are Mayim megulim and, in some communities, the saying of Baruch Hashem l'olam in evening prayers. From what I have read, the former is not in effect because there is no concern about snakes. I can only assume that the latter is not followed is because the prompting concern is lo longer a concern. But that line of thinking has not served to overturn the others.
I know that we have a strong tradition of tradition -- holding on to the teachings of previous generations. We feel (as per religious law) unequipped to undo pronouncements of earlier, greater generations. Except, apparently, when we do.