The presence of lead in the environment — a subject discussed in Neil deGrasse Tyson's show Cosmos last night — has been linked to a number of health problems, including kidney damage, anemia, and various forms of cognitive deficiencies. But the BBC reports that lead might also be to blame for an increase in violent crime following its introduction in petrol in the 1920s. Indeed, people exposed to lead tend to make poor decisions and to become more aggressive over time. And, according to various economists, the incidence of violent crime during the 20th century appears to correlate with the rise and fall of lead in gasoline. Unfortunately, this link is hard to validate, so the idea is speculative. Regardless, the tale of how various economists came to this conclusion — and why some researchers dismiss the lead-crime hypothesis entirely — is worth checking out. Read the full story over at the BBC.