I thought it was a fairly standard argument (well, within the canon of evolutionary science) that any gene which has apparently "negative" survival effects yet remains comparatively widespread must have "positive" surivival effects as well, even if they may not be obvious. There are certainly other examples of this (e.g. the link between sickle-cell anemia and increased resistance to malaria).

There's long been an empirical link between creativity and madness (hey, even the Greeks had spotted it). The intriguing thing is whether creativity is a survival trait at an individual level, if the "creation" can then be used by other members of society and they no longer need the creator. The society needs creativity, but if it doesn't benefit the individual, then it might die out. Arguably, this is why social structures have grown up which protect the creative - story-tellers and artists are as old as recorded history, after all (indeed, they ARE recorded history).