SANTA ANA, Calif. — We might never be able to feel sympathy for the speeding driver who swerves into our lane, barely missing the bumper, only to cut back into his original lane a quarter-mile later. But new research may at least help us understand him.

A new study at the University of California, Irvine, reveals that people with a gene variation that gives them less of a brain protein linked to memory retention performed more than 20 percent worse in a driving simulation than people who had higher levels of the protein.