New research traces the genetic pathways that toxins use to attack the developing brain.

Half a century ago, a scientist was trying to create a clean lab that he could use to study radioactive materials free of contamination. But no matter what he tried, his tests kept reporting that they were contaminated with lead. Finally, he realized the source: the lead was coming from the air itself—put there by decades of cars burning leaded gasoline. Eventually, the U.S. Congress passed the Clean Air Act, removing lead from gasoline.