For most of the 20th Century crime rose and rose and rose. Then, about 20 years ago, the trend reversed - and all the broad measures of key crimes have been falling ever since.Offending has fallen in nations whose governments have implemented completely different policies to their neighbours. If your nation locks up more criminals than the average, crime has
fallen. If it locks up fewer... crime has fallen. Nobody seems to know
for sure why.
Some people that believe the removal of lead from petrol was a key factor. Lead can be absorbed into bones, teeth and blood. It causes
kidney damage, inhibits body growth, causes abdominal pain, anaemia and
can damage the nervous system. Exposure to lead during pregnancy reduces the
head circumference of infants. In children and adults, it causes
headaches, inhibits IQ and can lead to aggressive or dysfunctional
behaviour. In other words - lead poisoning leads to bad decisions. The lead
theorists say the poison has a time-lag effect which could not be
understood until recently.
Research by Prof Jessica Wolpaw-Reyes, an economist at Amherst College
Massachusetts, tested if there was a causal link between
lead and violent crime by looking at the removal
of leaded petrol from US states in the 1970s, to see if that could be
linked to patterns of crime reduction in the 1990s. Wolpaw-Reyes gathered lead data from each state, including
figures for gasoline sales. She plotted the crime rates in each area and
then used common statistical techniques to exclude other factors that
could cause crime. Her results showed that states that experienced
particularly early or particularly sharp declines in lead experienced
particularly early or particularly sharp declines in violent crime 20
years later. The research also established different levels of crime in states with high and low lead rates. This relationship is
now coming up in other work on bullying, child behaviour problems,
teenage delinquency, suicide and substance abuse.
Supporters of the theory predicted that crime would
fall in other nations 20 years after the banning of leaded petrol - and
their theory appears to have played out in Europe. Leaded petrol was removed from British engines later than in
North America - and the crime rate in the UK began to fall later than in
the US and Canada. Lead theorists say that data they've collated and calculated
from each nation shows the same 20-year trend - the sooner lead is
removed from the environment, the sooner crime will begin to fall. Data now suggests that lead could
account for as much as 90% of the changing crime rate during the 20th
Century across all of the world.
The debate among biologists is now
moving further, to look at how improving nutrition could affect
antisocial behaviour. Lead is unlikely to be the whole story but given the broad
worldwide exposure and the evidence of how adversely lead
can affect behaviour, it makes sense that it is an important part of
the story.
BBC New website 21 April 2014: Did removing lead from petrol spark a decline in crime?
