Inactivity theory Inactivity theory is based on the concept of evolutionary pressure where creatures inactive at night were less likely to die from the predation of injury in the dark, thus creating an evolutionary and reproductive benefit to being inactive at night. Energy conservation Energy conservation theory posits that the main function of sleep is to reduce a person's energy demand during part of the day and night when it is least efficient to hunt for food.
This theory is supported by the fact that the body has decreased metabolism by up to 10% during sleep.
Restorative theory The restorative theory states that sleep allows for the body to repair and replete cellular components necessary for biological functions that become depleted throughout an awake day.
This is backed by the findings many functions in the body such as muscle repair, tissue growth, protein synthesis, and release of many of the important hormones for growth occur primarily during sleep.
Brain plasticity theory Brain plasticity theory is that sleep is necessary for neural reorganization and growth of the brain’s structure and function.
It is clear that sleep plays a role in the development of the brain in infants and children and explains why infants must sleep upwards of 14 hours per day.