The fascinating science of sleep and its role in human evolution
“Modern society, however, has given sleep a bad reputation. Busy as we are, we tend to pride ourselves on how less we sleep. Corporate executives see sleep as a waste of time, children would rather watch TV, teenagers prefer the transcendental wonders of their mobile phone. Vladimir Nabokov called sleep the “nightly betrayal of reason, humanity, genius”, Arnold Schwarzenegger advised those who want eight hours of it to “sleep faster”, and Margaret Thatcher prided herself in getting by with four hours. Some modern champions repudiate this notion—Roger Federer is said to sleep for more than 10 hours; so do Lebron James and Usain Bolt.
…In this virus-ridden world, it is perhaps the strongest weapon we have to build immunity, more formidable than vitamins and turmeric. It is an overlooked stress-buster, can delay dementia, and can manage our stress and obesity. While these facts were new to me, perhaps the most intriguing was that it is sleep that could have caused our evolutionary tree to branch off and separate us from our simian cousins.
…REM sleep that made us human. It is sometimes called paradoxical sleep, because the brain and heart patterns are identical to those when you’re awake. This is when short-term memory stored in the hippocampus is transferred to long-term memory in other parts of the brain. Here the brain and heart are active, we dream vividly, and our eyeballs rapidly move around. REM sleep renders our limbs totally inert. This is so that we do not flail around as we dream. REM sleep builds our cognitive abilities, so 80% of all sleep in babies is REM. We sleep to forget, but we also sleep to remember.
On the other hand, only 9% of a monkey’s sleep is REM. Limb-inertness induced by REM would imply that they would not be able to grasp the branches of the trees they sleep on, and fall. They also need to sleep light, since they are unprotected from predators. Around 15 million years ago, great apes solved this by making platforms and sleeping securely on them. The proportion of their REM sleep rose, raising their cognitive ability and consolidating memories. Some apes then started sleeping on the ground, and later, on beds, creating more space for REM sleep and a higher cognitive and memory ability, and eventually evolving into humans. Thus, it is the second stage of Upanishadic sleep, the “sleep of dreams” that helped make us human.”