nature

In the late 1980s, when the crack cocaine epidemic was ravaging America’s cities, Hallam Hurt, a neonatologist in Philadelphia, worried about the damage being done to children born to addicted mothers. She and her colleagues, studying children from low-income families, compared four-year-olds who’d been exposed to the drug with those who hadn’t. They couldn’t find any significant differences. Instead, what they discovered was that in both groups the children’s IQs were much lower than average.