> finding a linear negative relationship between lead levels in children and IQ was the smoking gun to prove that lead was harmful.
Lead toxicity was identified more than 2000 years before the first IQ test, and was rather extensively studied during the Renaissance. The combination of blood lead and IQ tests was important in quantifying the existence and impacts of particular kinds and levels of environmental exposure that had been assumed to be forms of levels that would not be hazardous, but it was not important to identifying lead as a toxin.
Lead toxicity was identified more than 2000 years before the first IQ test, and was rather extensively studied during the Renaissance. The combination of blood lead and IQ tests was important in quantifying the existence and impacts of particular kinds and levels of environmental exposure that had been assumed to be forms of levels that would not be hazardous, but it was not important to identifying lead as a toxin.