In evolutionary biology, punctuated equilibrium is the theory that evolution takes place through extremely small changes over a species history (equilibrium) but that occasionally, extremely significant and localized jumps occur rapidly (say in the span of a few generations). I think that this is a good model to explain cultural change over the course of a lifetime as well.
Societal norms, the “way it is”, change very slowly, until something big happens, something that pushes on the precociousness of a community until it makes a leap, discarding or devaluing some old beliefs and emphasizing new ones.
On a national level, look at what happened in the US after 9/11. The events of that day caused a collective shift in our national identity, 0ne devalued our feeling of safety at home, our belief that we are loved and admired throughout the world, and emphazied that the world was not the safe easy place we believed it to be after the fall of the USSR. The attacks at Virgia Tech probably had a similar, if more localized effect.
Pain and tragedy are the keys for us to reevaluate our lives and our situation, so it is no surprise that many big changes are born our of tragedy. Yet, even if their impact is harder to detect, I think positive events make a difference too. Many of us thought we were not ready for a Black President.
Barack Obama’s election shows we have reached a cultural tipping point — he may have won by barely 52%, but the fact that we have elected an African American president is truly a moment of cultural change in America. Every day, he will be in the news, in photos, creeping into our subconscious and changing our perception of people of other colors.