There&#x27;s a hypothesis out there, pushed by a few researchers citing each other (including one <i>Bell Curve</i> fan), that environmental lead from leaded gas and such caused reduced IQ and greater criminality among urban residents.<p>It&#x27;s not actually a remotely mainstream view among <i>any</i> sort of scientist. However, it has a lot of currency among left-of-center people uncomfortable with the legacy of urban renewal (aka &quot;bulldoze functional poor neighborhoods and stuff everyone in a housing project, then be surprised that things go badly&quot;) and the race-baiting nature of &quot;tough on crime&quot; measures that both parties adopted.