Chronotypes, such as early bird or night owl, are genetic and determined by the PER3 area on a person's genome.

People have a genetic sleep code called their chronotype, which dictates when their brain releases hormones like melatonin, cortisol, adrenaline, and dopamine.

A person's chronotype changes with age; babies are Lions, toddlers are Bears, adolescents become Wolves, and then it sets into one of the three or four types around age 23-24 for 25-30 years.

A 2020 study with nearly 800 students found a clear synchrony effect, where students performed significantly better when their class schedule matched their chronotype.

There are three known chronotypes, but Dr. Michael Breus is famous for discovering a fourth one.