![]() ![]() Stage one: Light N2 sleep comprises NREM one and NREM two.And these sleep cycles have three distinct stages of human sleep: Research has revealed we have four 90-minute long sleep cycles. What’s going on inside your brain when you’re sleeping? And deep sleep meant effective consolidation of these skills, which eventually led to higher cognitive intelligence, a point we’ll discuss later in more detail. For another, less sleep meant more time to pursue skills and knowledge. So the sooner they completed their quota of REM sleep, the better the chances of protection from incoming threats. For one, the risk of predators was higher in terrestrial environments. This means that early humans were pressured to sleep more efficiently in less time because of several factors. They have also postulated the Sleep Intensity Hypothesis to answer this question.Īccording to the Sleep Intensity Hypothesis, “early humans experienced selective pressure to fulfill sleep needs in the shortest time possible.” The risk of predators was one factor that pressured early humans to pack more efficient sleep in less time. Two evolutionary anthropologists, Charles Nunn and David Samson have done some groundbreaking research in this department. Why do we dream so much? Why do we dream when the deep REM state leaves us vulnerable to predators and dangers?īut first, how did human sleep evolve to be more efficient? The human REM to NREM ratio (22:78) is the highest proportion of REM to NREM of all primates. We spend a staggering 25% of our sleep in REM, which means we dream more. Higher sleep efficiency means that human sleep is shorter, deeper, and exhibits a higher proportion of REM. Compared to other species, humans sleep the least number of total hours. Good for them, but our sleep is way more efficient. Our primate relatives clock in between 13 and 17 hours of sleep each night. Compared to other primates, human sleep duration is the shortest, averaging seven hours. And that’s where our journey of a different type of dreaming began. Our ancestors could now capitalize on the benefits of deeper, more intense, REM-dominant sleep. This advantage put them in a unique position. There was fire against predators and the safety brought by sleeping in groups where someone was always guarding.įor the first time in history, our ancestors experienced the advantage of deep, efficient sleep. Second, we began sleeping in large, sentineled groups on stable ground beds, protected by fire, which would have fostered a safe sense of community.įor the first time in history, there was no danger of falling off a tree. First, it saved us from flesh-eating and blood-sucking predators while we slept on the ground. Second, it brought several physiological and cultural changes like beds, shelters, variation in chronotypes (how early or late someone sleeps), and controlled use of fire.Ĭontrolled use of fire is probably one of the most important factors as it did two things. Sentineled groups were an evolutionary advantage. One bad dream, one wrong turn while sleeping, and you would have been out of the gene pool. The transition to sleeping on the ground, first and foremost, eliminated the most significant danger of sleeping on the trees-lethal falls. At this point, our shared histories with our cousins began to diverge. And that was when they moved to sleep on the ground. But then, as our ancestors evolved to have erect bodies, they became unfit from living on trees. So like our closest cousins, our ancestors also built nests on trees to sleep each night (a tedious task that took up hours of our ancestor’s time). Sleep, hunger, blood pressure, alertness, and pretty much everything else in your body happen in sync with the circadian rhythm. Today, our closest living relatives are chimpanzees and bonobos, with whom we share 99% of our DNA. Our first cousins (like the Neanderthals) might have gone extinct, but our second cousins - monkeys, lemurs, and apes are pretty much still around. We belong to a group of Primates with over 200 species. We often like to think of our species as unique on this planet. REM sleep has changed our brains and how we think and solve problems. Let’s go back to the beginning to find out what happened. These benefits made some significant changes to our jumbo brains, and these changes are the very reason why we are at the top. This state conferred some unique benefits to our species. It’s this state of deep sleep in which we become as good as dead and dream of marvelous visions each night. Not to mention, colonized the entire planet. Fast-forward to the present day, their descendants have split the atom, walked on the moon, and sent probes on interstellar voyages. Some two million years ago, some of our hairy, tree-living ancestors descended from sleeping on the trees to sleeping on the ground. ![]()
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