In anticipation of the day, your body starts to churn out certain stress-related hormones during the later stages of sleep, says Jan Born, a professor of behavioral neuroscience at the University of T?bingen in Germany. His research team found that sleepers had more of the hormone adrenocorticotropin in their blood when they expected to be wakened at a certain time. Genes also play a role. One University of Kansas study pinpointed the gene KDM5A as the so-called alarm clock gene, which controls when our own personal “rise and shine” switch is flipped.—Sarah Klein, from huffingtonpost.com