Jerome Siegel, UCLA professor of psychiatry and director of the Center for Sleep Research at the Semel Institute for Neuroscience and Human Behavior at UCLA and the Sepulveda Veterans Affairs Medical Center is one scientist who is delving into the reasons behind our need for sleep.
It was thought that sleep has to provide a neurological benefit which cannot be attained during an awake state because sleep puts an animal in a vulnerable state, and prevents other functions from being carried out, such as a searching for food. Different species have varying requirements as far as sleep duration and patterns. Migrating birds can be awake for days at a time, whereas bears go into hibernation in the winter.
Siegel’s lab conducted a new survey of the sleep times of a broad range of animals, examining everything from the platypus and the walrus to the echidna, a small, burrowing, egg-laying mammal covered in spines. The researchers concluded that sleep itself is highly adaptive, much like the inactive states seen in a wide range of species, starting with plants and simple microorganisms; these species have dormant states — as opposed to sleep — even though in many cases they do not have nervous systems. That challenges the idea that sleep is for the brain, said Siegel.
Animals, including humans, have a selective system which can shift from a sleeping state to an awake state in milliseconds if the right stimulus occurs. The answer then has to do with metabolism and energy conservation.
In humans, the brain constitutes, on average, just 2 percent of total body weight but consumes 20 percent of the energy used during quiet waking, so these savings have considerable adaptive significance. Besides conserving energy, sleep invokes survival benefits for humans too — “for example,” said Siegel, “a reduced risk of injury, reduced resource consumption and, from an evolutionary standpoint, reduced risk of detection by predators.”
“This Darwinian perspective can explain age-related changes in human sleep patterns as well,” he said. “We sleep more deeply when we are young, because we have a high metabolic rate that is greatly reduced during sleep, but also because there are people to protect us. Our sleep patterns change when we are older, though, because that metabolic rate reduces and we are now the ones doing the alerting and protecting from dangers.”
It is an interesting hypothesis, but it still remains to be seen if it is in fact correct. If you are interested in this subject and would like a more in depth analysis, we recommend reading The Neural Control of Sleep and Waking.