McGill University Feb 2 2026 The familiar labels "night owl" and "early bird," long used in sleep research, don't fully capture the diversity of human internal clocks, a new study has found. The McGill University-led study published in  Nature Communications  found the two sleep-wake patterns, called chronotypes, contain a total of five distinct biological subtypes, each associated with different patterns of behavior and health. A chronotype is based on the parts of a 24-hour period when a