tl;dr version. Medical experts know that exposing babies to
lead causes brain damage + violent tendencies in later life. In the past, we exposed everyone to a
lot of lead, and violent crime rates always rise and fall ~20 years later, closely tracking the exposure levels, regardless of place and time, which should have been obvious but nobody put 2+2 together before recent years. Of course, the
guys who sell lead for a living are the only people who don't buy the science. The following are links to articles and studies and a couple of country-specific predictions.
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Detailed version with citations:
This was inspired by a conversation I had with a nurse in Australia claiming that violent movies and video games are primarily responsible for high levels of violent crime in Australia in recent years. She's seen the numbers of people coming into the hospital who have been beaten up, and if it's not movies and games causing it then "what else could it be?". I'm dropping this here to possible bring the issue to some peoples attention and as a space to collect my thoughts and some links on the issue.
Most people are aware of industrial pollutants and their negative effects on people and the environment. Individual lead poisoning in developing children has been found to be strongly associated with later lower IQ, aggressive tendencies and conduct of violent crimes in adulthood. It sort of makes sense that if poisoning one child with lead makes them more likely to commit violent crimes, then if you poison a whole lot of children at the same time with lead, then you'd expect the whole lot of them to end up committing a lot of violent crimes. But, of course, we would never do that, would we? Poison everyone with lead at the same time? How could that happen? Very easily in fact, since every road vehicle was a massive lead pumping machine back in the day, before they banned lead. Required reading
Forbes, summary of the evidenceMotherjones, this is really the definitive article on the issueOf course, a correlation between lead and crime itself wouldn't be very convincing, no more convincing than global warming is correlated with falling rates of piracy. But lead levels aren't the same everywhere, different people have different exposures, different places introduced and banned lead at different times. So, let's look at the breakdown of evidence instead:
First we have individual studies, where "Groups of children have been followed from the womb to adulthood, and higher childhood blood lead levels are consistently associated with higher adult arrest rates for violent crimes."
Then, we have neighborhood studies, where "Mielke has even studied lead concentrations at the neighborhood level in New Orleans and shared his maps with the local police. "When they overlay them with crime maps," he told me, "they realize they match up." "
There are inter-city studies (which I lack a spiffy quote for), but also state-vs-state studies, where "use of leaded gasoline varied widely among states <...> In states where consumption of leaded gasoline declined slowly, crime declined slowly. Where it declined quickly, crime declined quickly."
Then, you have international studies comparing countries. Each country has totally different times and rates at which they industrialized, had cars running on leaded gasoline, and later removed the lead: "in 2007 he published a new paper looking at crime trends around the world <...> what are the odds of that same something happening at several different times in several different countries? <...> Nevin collected lead data and crime data for Australia and found a close match. Ditto for Canada. And Great Britain and Finland and France and Italy and New Zealand and West Germany. Every time, the two curves fit each other astonishingly well. When I spoke to Nevin about this, I asked him if he had ever found a country that didn't fit the theory. "No," he replied. "Not one." "
So ... rather than a coincidental "good data fit" for the lead poisoning / crime theory "We now have studies at the international level, the national level, the state level, the city level, and even the individual level" which ALL tell the same story about lead vs crime.
Back to Australia, we started bringing in unleaded fuel 10 years after the USA did, 1985 in Australia vs 1975 in the USA. But on top of that, America was
much more aggressive with reducing lead levels in remaining leaded fuels than we were. In 1995 USA's average lead levels in leaded fuel were
0.026 grams/liter vs Australia's 0.3 grams per liter, and our total lead emmissions were
27 times the entire USA that year, not bad for a small population. So in terms of removing lead poisoning due to fuels, Australia was actually something like 20 years behind, since America made big efforts to reduce emissions in the early 1980s, and we did no such thing until a full ban in 2002. The prediction for Australia is therefore that violent crime due to lead poisoning should be spiking right about now, and will have dropped off heavily by 2020. I'll be checking in on this prediction over the years. You can bet that whoever is in political power in the next 5 years will get undeserved credit.
Now, lets put the theory to the test with a prediction based on unrelated data. Let's predict that the currently most violent countries will all have had a lot of leaded in the gasoline, at a point of 20 years ago (the lead time from babies with lead poisoning to adults with mental problems).
The top 4
countries by homicide are Honduras, Venezuela, United States Virgin Islands and Belize.
First, Virgin Islands was reported to use 26 times as much lead in gasoline as the
entire United States 20 years ago,
data from page 4 of this report. So US Virgin Islands did not remove lead from gasoline at the same time or rate as mainland USA. For an island of 100,000 people to pump out 26 times the lead from gasoline as the
entire USA is staggering. Virgin Islands was also putting in much more lead / liter than any other country, 1.12 grams / liter.
Second, in 1995 the only countries in Latin America which hadn't yet begun phasing out leaded gasoline were (from north to south) Belize, Honduras, Venezuela, Bolivia, Paraguay. (
page 3 here)
Bolivia and Paraguay don't top the list of homicides like the others. But a quick hypothesis would be that those two countries don't have a
high number of cars per person compared to the other 3. 1/6 have a car in Belize, 1/7 have a car in Venezuela, 1/10 have a car in Honduras (but the country is tiny so the pollution is extra concentrated), whereas 1/16 have a car in Bolivia, and 1/20 have a car in Paraguay. So this also fits the hypothesis. Countries with a higher degree of car ownership and/or high population density, which didn't start phasing out leaded gasoline before 1995 have the highest murder rates now, 20 years later.
Belize, Honduras and US Virgin Islands did act to reduce lead levels soon after these reports, which under the lead theory should mean their murder rates have peaked already, and that is what we see in news reports, with rates still high but starting to drop off. Venezuela was the last country in the Americas to ban leaded gasoline, in 2005, although they reduced lead concentrations by 2/3 from 1989 - 1999. Therefore, Venezuela should see homicide rates peaking about 2009 and heavily dropping off by ~2019. 2019 is also the year that President Maduro of Venezuela is up for re-election, so this is good news for Mr Maduro's re-election chances :/ although the coming drop in homicide rates will have nothing to do with his policies, politicians always end up getting credit for whatever happens on their term.
This is an interesting article about the murder rate in Venezuela. The government has one figure, and the opposition has a different, much huger figure (estimated in a pretty silly way though, exponentially extrapolating a short-term trend towards infinity). There is a third set of figures collected by a group which has gone completely unnoticed by the two political camps, which makes it more plausible that it's raw data not affected by politicking - the country's Ministry of Health collects information on births and deaths, and their count of violent deaths is in the middle of the two conflicting estimates, though this figure has never been cited by politicians from either party in the country. The Ministry of Health data suggests murders peaked in 2008 and have fallen ever since.
Who else hadn't started bringing in unleaded gas by 1995? Almost all of Africa and the Middle East, basically.
