People are typically biased toward noticing either good or bad events, and a common genetic variation may underlie such tendencies for optimism or pessimism. Scientists at the University of Essex in England investigated serotonin, a neurotransmitter linked with mood, and explored how 97 volunteers preferred different kinds of images. People who carried only long versions of the gene for the serotonin transporter protein—which controls levels of the neurotransmitter in brain cells—tended to pay attention to pleasant pictures (such as images of chocolate) while avoiding negative ones (such as photographs of spiders). Those with a shorter form showed opposite preferences, though not as strongly. The findings, in the February 25 Proceedings of the Royal Society B, help to explain why people may be less prone to anxiety and depression and could lead to therapies that help some look on the bright side.