In the 1960s, a 17-year-old high school student named Randy Gardner set out to break a world record. He stayed awake for eleven straight days. At first, it seemed like a stunt: he gave interviews, played basketball, even cracked jokes with reporters. But as the sleepless days dragged on, his body and mind began to break down. He forgot simple facts, slurred his speech, and became irritable and paranoid. Years later, Gardner admitted the cost was permanent. He developed severe insomnia and described it as “karmic payback” for the experiment. 

His story became one of the most well-documented cases of sleep deprivation, and supported later studies of “microsleeps.” 

The human brain interprets sleep loss as a threat, something modern science has confirmed again and again: Sleep deprivation rewires the brain in damaging ways. It slows communication between brain regions, reduces blood flow, and can make a young brain resemble an aged one. Yet, strangely enough, human beings are built to need less sleep than most of our closest primate relatives. Our evolutionary story with sleep is complicated, what once gave us an advantage now works against us. 

The Ancestral Trade-off 

For our ancestors, darkness was both a danger and an opportunity. Sleeping deeply left them vulnerable to predators. Staying awake, however, meant guarding the group, telling stories around the fire, and passing on knowledge. On the other hand, a person  who slept too deeply risked being attacked by predators, missing a shift to guard the camp, or losing opportunities to learn from peers. Anthropologists argue that this trade-off gave humans an advantage; our ancestors may have shortened their sleep to gain extra hours for survival and social connection. We learned, bonded, and survived, staying awake longer was strategy not distraction. 

Humans are unusual in this regard. Most primates with our brain size and body structure are predicted to need around nine to ten hours of sleep. We get by with less ( we only need about seven). One theory is that our brains became more efficient. We pack in a higher proportion of REM sleep—the dreamy, memory-strengthening phase—than other primates. That efficiency allowed us to cut total sleep without losing all of its benefits. 

Evolutionary biologist Charles Nunn put it, “Humans may have carved out extra hours in the night not to rest, but to think, learn, and connect.” It was a bargain with nature: less sleep, but more time awake to build culture, share knowledge, and guard the tribe. 

The Modern Mismatch 

Fast forward to today, and the very trait that once helped us survive is working against us. Unlike our ancestors, we aren’t staying up to protect our families from predators. We’re staying up to meet work deadlines, scroll social media, or stream one more episode of a show. 

And the toll is enormous. Chronic sleep loss is now linked to depression, dementia, obesity, diabetes, and heart disease. Economists estimate that billions of dollars are lost each year from accidents and reduced productivity caused by insufficient sleep. One-third of adults in the U.S. and Canada report they don’t get enough rest. 

Psychologists explain why this is so draining: when our brain doesn’t get enough sleep, it struggles to regulate emotions, process memories, and filter toxins. In simple terms, we’re asking our bodies to run a marathon every day without giving them time to recover. And unlike our ancestors who accepted some risk when they sacrificed sleep, we’re paying the price in ways they never did. 

Staying Fit Might Help 

If sleep deprivation is so damaging, what can help us cope? Surprisingly, one protective factor may be fitness. Recent research shows that people with higher levels of cardiorespiratory fitness  perform better on memory tasks after a sleepless night compared to those with lower fitness. 

Note that Fitness in this context wasn’t about lifting heavy weights, it was about cardiorespiratory strength (the ability of the heart and lungs to deliver oxygen to the body). The explanation is still being studied, but evidence points to fitness enhancing brain connectivity and resilience. It seems that physical activity doesn’t just strengthen the heart and lungs; it may also buffer the brain against some of the cognitive costs of lost sleep. 

This does not mean exercise is a substitute for rest. Nothing can fully replace sleep. But it suggests that regular movement (such as running, cycling, swimming, even brisk walking) may act as a cushion when sleep inevitably falls short. 

What this means for us 

It would be easy to conclude that the solution to sleep deprivation is simply to sleep more. But modern life often makes that unrealistic. Parents, healthcare workers, pilots, night-shift staff, and countless others live in schedules that defy the body’s natural rhythm. For them, sleep debt is not a choice but a condition of life. 

This is where policy comes in. Later school start times for teenagers, healthier shift scheduling, and abandoning daylight savings time are just a few interventions that researchers advocate. On an individual level, good sleep hygiene (such as consistent schedules, dimming screens, and managing caffeine) matters too. And if sleep can’t be extended, fitness becomes even more valuable as a protective layer.