We’re really just flies on the wall, scientifically speaking
According to the Nobel Assembly’s press release, the four scientists isolated a gene that controls circadian rhythm using fruit fries as a model. “They identified additional protein components of this machinery, exposing the mechanism governing the self-sustaining clockwork inside the cell. We now recognize that biological clocks function by the same principles in cells of other multicellular organisms, including humans.”
Simpler life forms — like fruit flies and even one-celled organisms — developed circadian rhythms to get ahead of changes in their environments. That means they learned to predict everything from when their environment would get hotter (to avoid burning to death) to, eventually, the movements of their predators and prey.
Today, humans need these rhythms for more complex, but no less essential, reasons.