One thing that strikes you when reading about periods of dramatic upheaval, as signaled by a sustained rise in the homicide rate, is the youth rebellion that coincides with it. It's not just young people acting even more prototypically youthful -- becoming more violent and horny -- but a broader behavioral and cultural experimentation.
The clearest sign of this is a widespread disobedience of adult wishes and commands when it comes to dating and mating. Usually these come from parents who want their children to marry in a way that will benefit themselves and the wider family, not just now but into posterity, which is not entirely the same as the way that will benefit the son or daughter themselves. But they could also come from non-kin in their parents' age group. Against that, the young person pursues only who they want to.
This practice of romantic love shows up in statistics during the recent crime wave -- those young people's parents certainly did not want them having sex so early and with so many partners. During previous waves of violence, the concern about romantic love -- whether for or against -- starts to take over much of the cultural products. The 14th C. saw such a wave of both violence and romantic impulsivity, as did the Elizabethan-Jacobean period, and the Romantic-Gothic period. (The U.S. had another wave from at least 1900 to 1933, and the Roaring Twenties were the culmination of a youthful, romantic movement away from Victorian and Gilded Age sensibilities.)
Are these youth rebellions irrational, misguided, harmful, and so on? Probably not. (We are only ever talking about "compared to the alternatives.") Why not?
Behavioral strategies, and codes of morality that regulate behavior, are like tools that help a person make it through life successfully. Like other tools (and cultural thoughts or practices in general), they may become outmoded if the environment changes. If sea levels swallow the land, we will have to throw out a lot of things that just won't work underwater and we'll have to add things like goggles, air tanks, etc. And of course if sea levels don't change that radically, our existing toolkit will work just fine as it is.
It sounds silly to state something so obvious, but most people don't get it in the context of behavioral strategies and moral codes. The "don't trust anyone over 30" crowd is wrong because if the relevant features of the world haven't changed so much in 100 years, then grandma probably does know best and you shouldn't waste time experimenting so much. On the other hand, the "respect the status quo" crowd is wrong because if the world has changed a lot, then today's young people can no longer adapt themselves to their environment using the cultural tools of their recent ancestors.
As with genetic adaptation, they have to resort to trial-and-error -- blind mutation -- if they ever want to stumble upon what works best in this new environment. Most experiments will fail, just like most genetic mutations are harmful. But the ones that begin sweeping throughout a population are probably not just getting lucky (especially if the population is large) -- they're the ones that lead people successfully through life in the new environment.
You cannot object that, sure, the new mix of behaviors and codes can be successful, but they may still be fundamentally immoral. Remember -- compared to the alternatives. Take an extreme case, where the elders preach non-confrontation and peace. In a world of falling violence levels, like most of the 18th C., that advice works fine. But when violence levels soar, how moral is it to let the resurgent forces of evil just walk all over you and everybody else? Existing institutions are always impotent to stem or reverse the crime wave, so outsourcing the job is not very satisfying. You have to develop a greater propensity to use violence in order to protect yourself and others, and occasionally you'll even have to act out that impulse.
The same applies to the full range of newly successful behaviors and codes. In a safe and monogamous world, perhaps the elders really do "know what's best for you" by advising you to pick a certain type of mate, but only one of them, and to stay with them forever. However, when violence soars, this "good dad" strategy may be for suckers only, as I detailed in a recent post about why females will shift to a more promiscuous strategy in more dangerous environments. The elders may also be out of touch when it comes to moral arguments for monogamy that stress community harmony -- in the new world, an attempt to enforce monogamy may only lead to greater resentment and destructive behavior, unlike such an attempt in a safer and more well-behaved world.
This evolutionary way of looking at things -- that the culture of the elders is wise for the young to the extent that the environment has remained the same -- also shows why for every youth rebellion there is a later youth counter-rebellion. Again the main environmental change that matters is the level of violence. When the violence level cycles into a much safer phase, then the adults -- who came of age during violent times -- preaching the value of self-defense, courage, etc., will have little to contribute to the young, who don't need a lot of that anymore. Advice from middle-aged males to younger males that they should get out and cat around more will fall on deaf ears -- safe times cause greater monogamy, so that strategy would go nowhere. Or at least, not where it went during the sexual revolution that the middle-aged guy lived through during violent times.
As with youth rebellions, we have clear statistics on the youth counter-rebellion of the past 15 to 20 years, after the crime rate began plummeting. I've gone over that enough by now that it doesn't need repeating. There was a similar self-domestication of young people during the mid-'30s through 1950s, during the Victorian era in Europe, during the long fall in violence from roughly 1630 through 1780 (peaking during the Age of Reason), and during the interval between the 14th C. and late 16th C. waves of violence (peaking during the heyday of Renaissance humanism).
We don't typically think of young people wanting to live tamer and more boring lives than their elders, but this analysis shows why we should expect to see it, and when it should happen. Fortunately for skeptics, we're living through just such a phase right now, so don't take my word for it. Middle-aged people today have more exciting tastes in music and movies, are more likely to have unprotected sex, and drink and smoke more frequently; meanwhile the teenagers and 20-somethings are a bunch of young fogies.