Although the 1985 arrival of crack cocaine in large U.S. cities had dire consequences, including a doubling of the homicide rate among black males aged 14 to 17, the epidemic’s social ills subsided after a few years, despite continued high use of the drug, says a team led by Roland G. Fryer Jr. of Harvard. After experiencing severe disruption from this technological innovation, illicit drug markets settled down and crack prices fell sharply, hurting the business’s profitability and reducing competition-related violence among dealers, the researchers say.