Sold.
I actually like both of these theories… A lot of violent criminals simply never get born in the first place…and our society is getting less aggressive, less macho, overall. And it might be partly due to video games! Fewer people seem to be on the hiking trails, at the beach, out in the desert. I don’t have any real stats, but it seems that not only are we becoming more obese as a nation, we’re becoming less physically active in all ways. That this includes violence is a side-benefit.
My great-grandparents were born during the US Civil War, so that bar could be higher. 
That research on leaded gasoline seems pretty damn conclusive. Thanks for sharing that article, it was a great read.
Some other factors accoding to Levitt (Freakanomics author) may include more police, longer prison sentences, the Roe v Wade decision and decline of crack cocaine use. The video game/internet use arguments above are also interesting.
Levitt, Steven D. (Winter 2004). “Understanding Why Crime Fell in the 1990s: Four Factors that Explain the Decline and Six that Do Not”. Journal of Economic Perspectives 18: 163–190.
I think Cellphones might have something to do with it. The mid 90’s were when cellphones started to get into peoples hands and they have increased every year. Everybody can make an instant 911 call now a days. Everybody can call help. That has to have a huge effect on criminals.
The lead thing wreaks of some type of non-causal coincidence.
The right complains about the feminization of America (usually cultural, not chemical, but close enough), but they never mention the good points! Plus, we’re just not as ambitious as we used to be. Kill someone? Feh, that sounds like a lot of work. Let’s go smoke a bowl and get some Taco Bell instead.
But,
Would be interesting to see the rate of use of cellphones in those states.
Well first of all, a study of how lead affects the brain to get an actual connection is in order.
What the study sounds like to me is that Gen X kills less people than any previous generations. Gen Y even less.
You can probably attach a lot of things to this change. Lead, available abortions, cell phones, the Internet, healthy lifestyles, less pesticides in food, etc…
That sort of correlation would be one hell of a coincidence.
I’m telling you, video games and internet porn. Without it we would be living in mad max world.
Well, it should then be easy to do. But they also did check for a lot of that in the study, in any case, I expect that others factors are likely to be found, but so far this one has a lot of evidence going for.
Since people commit violence against someone’s person or property because they lack respect for that someone’s person or property, I would attribute a decrease in crime with an increase in respect for individual’s and their property. So basically an improvement in morals is responsible.
But this is essentially just rephrasing the question. The question of what caused crimes to decrease becomes the question of what caused morals to improve.
The lead theory sounds like the reverse of the theory about lead in water pipes that was once - rather foolishly - fashionable to see as the real reason for the decline and fall of the Roman Empire.
Aging society. Less youngsters, more old geezers. Old folks are boring. They can’t even be bothered to murder a few people. They’re also less passionate, experimental, creative, inventive, and more risk-averse in general. Less passionate drive. It could be interesting to see if falling crime rates correlate to a general decline in dramatic new ways to approach society and life with.
Could a project comparable to the Apollo Moon landing program or the 60s youth rebellion be conceived of today?
The problem with a lot of these explanations, like lead and abortion, is that if they were true you’d see the new generation be much less violent than the older one. But that isn’t what happened, AFAIK. Everyone became less violent all the sudden.
See the second graph at this link. It compares incarceration rates by age between 2001 and 2011.
What it shows is that more people over 40 are locked up than there used to be, but way fewer people under 30, with people in their 30s about the same.
So for the incarceration theory to hold water, you’d have to believe that keeping fortysomething and fiftysomething criminals off the streets is what’s preventing a crime wave. I doubt you can find a criminologist who would argue that: crime’s primarily a young man’s game.
And the young men are committing way fewer crimes than they used to.
The current under-30 generation is much less violent than the older generation was *at the same age. *
Now every generation gets less violent as they get older. So you really need to compare how one cohort is doing at a given age, with how another cohort is doing at the same age. Comparing across ages doesn’t tell you much.
The first post-lead cohort is only starting to enter its 30s, so we can’t yet compare its crime rate in its 30s and 40s with that of the last fully leaded cohort.
ETA: Here’s a set of links to a bunch of Kevin Drum’s posts on specific aspects of the lead theory.
I think the reduction in pollution and also the inactivity theory are pretty good.
In so far as the reason for declining sperm counts is less testosterone and testosterone in young adult males is associated with violent behaviors … That sure seems likely to be a factor.
Internet as part of decreased face to face physical competition between young adult males.
How about the fact that many of the more impulsive young adult males are now identified in childhood as having ADHD and medicated by the point they are greatest risk of violence?
Yes this was kind of meant as a response to the lead argument. I don’t know if i buy that lead poisoning automatically makes you violent. It may make you more subject to impetuous actions, but if your impetus is to do good, I don’t see how lead poisoning would make you evil. Would a society of Jesuses and Buddhas regress to violence due to lead poisoning? I’d say no.
Also the abortion argument is strange because many people would view an increase in abortion as an increase in violence in and of itself, what happened was merely a recategorizing of the type of violence from illegal to legal. Also, you would have to ask whether or not the forced taking from one to give to another is violence, broadly defined.
The inactivity theory would rest on an increase in productivity that allows people to live these lifestyles. An increase in productivity could also explain an improvement in morals. If more and more people have property of their own, they are more likely to have empathy for those who are robbed.
Kids learn morals from their family first, then probably school. Maybe increased education on moral issues is responsible.