Researchers have picked out genes that influence various personality traits, including:

Novelty seeking. In 1996 psychologist Richard Ebstein of Herzog Hospital in Jerusalem and his colleagues identified a peculiarity in the genetic blueprint for a receptor that responds to the neurotransmitter dopamine that is more common among people who score high on a test of novelty seeking. Such people tend to be relatively impulsive, exploratory, fickle, excitable, quick-tempered and extravagant.

Recent work confirms the potential of variation in the same dopamine receptor gene, dubbed DRD4, to influence such traits - this time in birds. In 2007 biologist Bart Kempenaers and his colleagues at the Max Planck Institute for Ornithology in Seewiesen, Germany, reported that another even smaller oddity in this same gene is associated with exploratory behavior - an expression of novelty seeking-in great tits, birds that are native to Europe and Asia.

Attention deficit. Researchers have gathered considerable evidence that genes play a role in attention-deficit hyperactivity disorder (ADHD) in children. Because defects in dopamine transmission have also been linked to ADHD in young people, scientists have sought variants of dopamine receptor genes that pose a greater risk for the disorder. So far they have identified several. In 2007 for example, psychiatry researcher Philip Shaw of the National Institute of Mental Health (NIMH) and his colleagues reported evidence for a connection between the human novelty-seeking DRD4 variant and ADHD and also unveiled a possible neurological basis for its effect. In a study of 105 children with ADHD and 103 unaffected kids, the researchers found that those who had both ADHD and the risky form of the gene bore unusually thin tissue in two regions of the brain that govern attention. The brain tissue in these regions was somewhat thicker in children who had either the genetic variant or the disorder and was thickest in those who had neither a diagnosis nor that genetic peculiarity, hinting that this dopamine receptor variant might influence attention by affecting the thickness of the brain in certain places.

Antisocial behavior. In 2002 Avshalom Caspi of King's College London and his colleagues reported that one version of the gene for monoamine oxidase A (MAOA) - an enzyme that breaks down key mood-regulating chemicals, among them serotonin - is more common among violent, antisocial men. But men bearing this form of the gene, which is thought to decrease enzyme activity and thereby boost serotonin levels, were more prone to impulsive violence only if they had been abused as children.

In 2006 psychiatrist Andreas Meyer-Lindenberg, now at the Central Institute of Mental Health in Mannheim, Germany, and his NIMH colleagues reported a possible neural mechanism for this interaction. Carriers of the violence-linked version of the gene showed reduced volume in areas of the brain that govern emotion and displayed heightened activity in their brain's fear processor, the amygdala, while looking at angry and fearful faces. They also displayed depressed activity in higher brain regions that regulate the fear hub.