We know that lead exposure can be dangerous. We know that it can cause brain damage. But what levels are dangerous. How does that damage express itself? And how do you separate the effects of lead poisoning from a whole host of other potentially dangerous, damaging factors? Last week, Mother Jones had a well-done article about research that is drawing connections between leaded gasoline and the crime wave of the mid 20th century. That's a hypothesis. It's a hypothesis with a lot of correlational evidence. But it's not proof. I recommend reading public health researcher Scott Firestone's excellent article that delves into the details of the studies from the Mother Jones story. It's a great look at the lines between public health as a science and public health as activism and it helps shine some light on why seemingly airtight cases aren't always immediately acted upon.