I've always imagined they have a lot of sex in the vaults. Not because I'm kinky, but because I'm a wannabe sociologist. And sociologists have a free pass to think about these things.
It should very much be a Fallout perk. "Sociologist".
For those of you who don't know, Fallout is a series of computer games set in a post-apocalyptic future, where the nukes have done their scientific magic. Those humans that have survived are either heavily mutated, or the descendants of those who happened to be in fallout shelters - vaults - when the bombs fell.
Now, picture the life in these vaults. Going outside isn't really an option, because of the brutal levels of radiation. And since going outside isn't an option, you're pretty much stuck with what you have inside the vault. Which, being built to last for generations, isn't going to change all that much. The physical environment is, for all intents and purposes, a given - like a mountain, it remains the same, unchanging.
The cultural environment isn't likely to change, either. The influx of new books, songs, ideas and news is naturally going to be rather limited, and on the whole you are stuck with what you happened to have on hand as the bombs fell. It goes without saying that taking a pleasant stroll to the public library downtown isn't really on the list of things to do.
As it stands, the only interesting thing going on in a vault is what the other inhabitants are doing. And because of the lack of any other action of any kind, social relations, tensions and processes are magnified by a brutalfold. In an ecology where relations are the only relevant information -
Well. It becomes really important who sleeps with whom. And in the absence of long term distractions, sleeping with people becomes a very attractive prospect indeed.
Even more so than under pre-apocalyptic circumstances.
I can only imagine the tension that the inhabitants must feel. Every move is scrutinized, analyzed, made into public knowledge and on the whole neither forgiven nor forgotten. Politics, metapolitics and metametapolitics is the name of every game, and the urge to get away from this will either drive people insane, horny or both -
Makes you think, doesn't it?