For living beings, the biological clock was both an important and an unimportant concept.
During sleep, a creature's brain inevitably entered a dormant state—or rather, the modern concept of "sleep" referred precisely to the brain's rhythm. In other words, strictly speaking, lower life-forms lacking a nervous system and an independent brain did not sleep.
Of course, even without brains, living beings possessed "dormancy," in which bodily metabolism decreased and activity slowed. Though sleep and dormancy appeared nearly indistinguishable, strictly speaking, they were two different concepts.
In the Aura Universe, "dormancy" also involved changes in the state of the soul, making it an equally complex and rigorous concept.
But the biological clock was more like a special punishment mechanism.
For higher life-forms with brains, sleep meant temporarily shutting down the "operating system" known as the brain, forged through hundreds of millions of years of evolutionary force, leaving only a few instincts running in the background. It meant halting all conscious activity, lowering one's guard against predators, casting off defenses, and exposing oneself to an extremely dangerous state. Moreover, sleep severely slowed a creature's efficiency in obtaining food—after all, few living beings could keep acquiring food while asleep.
If there really were any, they could only be... humans hooked up to an IV drip.
Think about it: a person spent one-third of their life asleep—spent meaninglessly. Shouldn't that itself be terrifying?
For animals, the cost of sleep was this immense. Accordingly, its benefits ought to have been immense as well.
Perhaps many people's first reaction would be, "Nonsense. Mortals will die if they go without sleep for several days." But on closer thought, where was the evolutionary cause and effect in that?
Was "you die if you do not sleep" an established fact, and living beings therefore acquired the ability to "sleep"?