We always hear/read about the symbolism present in the traditons and trappings of various holidays, particularly old religious ones. For example, Christmas evergreens representing eternal life, Easter egges symbolizing re-birth, etc. Were these symbols originally created with those reasons in mind or did they simply evolve randomly, and have their supposed meanings applied post facto in an attempt to rationalize them?

Jewish traditions are the ones I know best, and I can tell you that there are three broad categories:
[li]Where a tradition is started with specific ideas and symbolism in mind[/li][li]Like #1, but more symbolism is attributed to it later on, and the original may or may not be forgotten[/li][li]Where something is done for purely practical reasons, but this is forgotten, and people continue doing it anyway, and then symbolism is invented for it; eventually people may come to forget this process, and think that this was the original reason for it.[/li][/ol]
Needless to say, some people can get pretty emotional about this, and disagree about which category any particular tradition belongs to. Which is why I’m not giving any examples.

That’s more or less what I expected.