Chronotypes refer to the body's natural inclination to sleep or be awake at certain times of the day. It is a deeper examination of the early-bird-night owl spectrum. Besides wake and sleep times, chronotypes influence other aspects such as appetite, physical exertion, and body temperature. Research by Dr. MichaelBreus suggests that genes heavily influence chronotypes. The PER3 gene associated with the circadian rhythm influences morningness. Long alleles of this gene increase the likelihood of being an early bird, while shorter alleles increase the chances of being a night owl. While the circadian rhythm is influenced by environmental factors such as light, sound, temperature and other sources of stimuli, the chronotypes are influenced by genes. Therefore, altering the circadian rhythm is easier than changing the chronotype. The Four Chronotypes Dr. Michael Breus popularized these chronotypes. The four chronotypes are named after animals that best exhibit these traits...