Last night, as I was lying in bed drifting toward sleep, my brain decided this would be an excellent time to question one of the strangest features of human existence: why in the hell do we still need so much of it? From an evolutionary standpoint, sleep initially seems like a terrible arrangement. If survival favors organisms better equipped to stay alive and reproduce, being unconscious for roughly a third of your existence feels like something natural selection should have aggressively worked to eliminate. Every extra hour awake is another hour to find food, avoid predators, build shelter, have sex, invent civilization, or at least keep an eye on whatever is standing outside the cave. Surely somewhere along the evolutionary line, the people who could function perfectly on four hours should have enjoyed an enormous advantage over everyone spending eight hours completely defenseless.
And yet here we are. Seven-ish hours later, every day, the lights come back on.
Which led naturally to my more pressing concern: what in the hell is the committee doing in there while I’m gone?
I’ve written before about the committee, my affectionate name for the collection of voices, impulses, perspectives, memories, moods, arguments and competing priorities that somehow combine to create the experience I call “me.” During waking hours I at least maintain the illusion that somebody is chairing the meeting. There is a narrator sitting at the head of the table taking credit for decisions and pretending to maintain order. But every night that guy is forcibly removed from the building. Consciousness shuts down, the doors lock behind me, and apparently the committee spends the next seven hours doing whatever it wants without adult supervision.
The more I thought about it, though, the stranger sleep became. Evolution has had an absurd amount of time to solve this problem. Sleep makes an animal vulnerable. You cannot forage while asleep. You cannot reproduce while asleep. You cannot defend territory, notice danger or run from whatever has decided you look delicious. Even humans, who eventually invented locks, mattresses and alarm systems, spent almost all of our evolutionary history sleeping in circumstances considerably less secure than my bedroom. If consciousness could simply remain online indefinitely without consequence, that organism should have an obvious advantage.
Instead, sleep survived.
Not just in us, either. Sleep, or something remarkably like it, appears throughout the animal kingdom. Evolution has developed all kinds of strange compromises around it. Some animals sleep very little. Others can let portions of the brain rest differently from others. Humans themselves appear to sleep less than we would expect compared with other primates, suggesting evolution has already squeezed some efficiency out of the system. But it never eliminated the shutdown entirely.
That realization flipped my original question around.
Maybe the mystery isn’t why evolution failed to get rid of sleep.
Maybe the mystery is what sleep must be accomplishing for evolution to tolerate it.
We tend to talk about sleep as though it were simply rest. The brain worked all day, became tired and now needs to recharge. It is an intuitive explanation because that is how sleep feels from the inside. You get exhausted, disappear for several hours and wake feeling better. Battery depleted. Plug human into mattress. Battery replenished.
But the brain isn’t remotely inactive while we sleep. It changes operating modes.
Memories are consolidated and reorganized. Synaptic connections are strengthened, weakened and recalibrated. Hormonal activity changes. Different patterns of neural synchronization appear. Metabolic and maintenance processes shift. Emotional experiences seem to be processed differently. During REM, the brain can become extraordinarily active while largely disconnecting itself from the external world and generating its own internal realities. Even the architecture of sleep matters: light sleep, deep slow-wave sleep and REM appear to perform overlapping but distinct functions, cycling throughout the night rather than simply providing one homogeneous state called “unconscious.”
Attempts to cheat that architecture make the whole thing more interesting. I remembered reading years ago about people experimenting with extreme polyphasic sleep—tiny naps scattered throughout the day with the hope of training the brain to dive immediately into REM and function on only a couple of hours of total sleep. The idea has an appealing hacker logic to it: perhaps most sleep is inefficient padding, and if we could force the brain directly into the important stages, we could reclaim six hours of every day.
Except our growing understanding of sleep suggests that REM isn’t some magic ingredient that can simply be extracted from the recipe. Deep sleep matters. Sequencing matters. Continuity matters. The transitions apparently matter. Trying to grab only the parts of sleep we currently understand is a little like discovering that a computer performs backups overnight and concluding that everything else happening while you’re asleep can therefore be deleted.
Maybe the committee has more departments than we know about.
And that is where my half-asleep evolutionary question started turning into something closer to awe.
What if consciousness itself interferes with some of the brain’s necessary work?
During waking life, the brain is constantly being bombarded with information. Eyes are sending data. Ears are sending data. The body is reporting its condition. Memories are being retrieved. Predictions are being made. Decisions are occurring. Attention is bouncing around. New experiences are modifying neural connections while those same connections are simultaneously being used to interpret the world.
Maybe there are simply certain kinds of maintenance you cannot perform while the store is open.
So every night the committee turns the sign around.
CLOSED.
Customers out. Doors locked. Inventory begins.
Someone starts moving things around in memory. Someone else adjusts the emotional filing system. Maintenance crawls underneath the machinery. Connections that proved useful yesterday get reinforced. Others weaken. Chemical systems change schedules. Dreams begin running bizarre simulations using fragments of childhood, yesterday afternoon and a person you haven’t thought about since 1997. Somewhere inside all of this activity, the organism is being prepared to wake tomorrow believing it simply “rested.”
What fascinates me most is that the person who normally claims ownership of the whole operation is absent for nearly all of it.
That may be part of why sleep remains so mysterious to us. Consciousness is wonderfully positioned to study waking consciousness because it is present for the experience. I can observe myself thinking. I can notice perception happening. I can catch memories emerging. I can watch members of the committee argue and occasionally even notice which one has seized the microphone.
But sleep creates a peculiar problem.
The witness leaves.
The organism continues doing enormously important things, but the narrator isn’t there to watch them happen.
Seven hours later the doors open again. I wander back inside. The furniture has moved slightly. Some memories seem clearer while others have faded. Yesterday’s overwhelming problem suddenly looks manageable. An idea appears that wasn’t there before. My body has changed. My chemistry has changed. My brain has physically changed. There may have been several dreams, although most have already disappeared before I can inspect them.
Then the narrator sits back down at the head of the table and resumes acting like management.
Perhaps that is what I find most delightful about sleep now. It is a nightly demonstration of how little conscious control is required for this organism to remain itself. I disappear completely for hours at a time and the system does not panic. It does not wait for instructions. It simply gets to work. In fact, judging by how badly everything begins functioning when I repeatedly refuse to leave, the committee may prefer having the building to itself.
So my original question—why haven’t we evolved beyond needing sleep?—now feels backwards. Sleep has survived precisely because whatever happens when we disappear is important enough to justify disappearing.
Natural selection has spent hundreds of millions of years looking for efficiencies. If shutting consciousness off for hours every day were merely an unfortunate habit, something somewhere probably would have found a better way by now. Instead, evolution keeps paying the extraordinary price of vulnerability, inactivity and lost waking time.
Which suggests that every night, behind the locked doors of consciousness, something extraordinarily valuable is happening. Unfortunately, management is not invited. And every morning I wake, stretch, walk back into headquarters and confidently resume running an organization that apparently functions perfectly well without me. I can only assume the committee waits until I’m fully awake before laughing.