If sleep doesn’t serve an evolutionary purpose, then it is the biggest mistake evolution ever made.”
These words belonged to Allan Rechtschaffen (1927–2021), the late University of Chicago professor and one of the founding fathers of sleep research. His point was simple: if sleep were useless, evolution would have phased it out. The fact that it exists—and is universal among mammals—proves just how crucial it is.
For millennia, food and exercise were celebrated as the cornerstones of good health. The ancient Greeks, for example, linked a balanced diet and movement to human flourishing. Sleep, by contrast, was long treated as an unavoidable inconvenience—a passive state, little more than a “necessary evil.”
Science now tells us otherwise. Sleep plays a critical role in immunity, metabolism, learning, memory, and countless other processes essential to survival.
The Hidden Costs of Too Little Sleep
The evidence is mounting. One striking example comes from a 2023 study published in The Lancet, based on data from the U.S. Centers for Disease Control and Prevention (CDC).
The findings were stark: chronic sleep deprivation was linked to poor mental health, higher risk of strokes, obesity, and hypertension. The tipping point? Sleeping less than seven hours a night.
This is not about the occasional late night—it’s about what happens when short sleep becomes the norm.
When Science Meets Real Life
Of course, applying this knowledge is easier said than done. Parents of newborns know the reality of fragmented nights, as do shift workers whose jobs demand sleepless hours.
But for those of us without such constraints, researchers say there are practical lessons worth adopting.
One of the leading voices is Elizabeth Klerman, professor at Harvard Medical School and a pioneer in circadian rhythm research. In her lectures, she emphasizes two key truths:
- Nobody sleeps perfectly. No one falls asleep the moment their head hits the pillow.
- If you need an alarm clock, you’re not getting enough sleep.
Her advice is deceptively simple: if you want eight hours of rest, give yourself at least 8.5 hours in bed. That buffer allows for the natural delay of drifting off and ensures waking up feels natural—not forced. Ideally, wind down with reading or quiet relaxation before sleep.
Sounds almost luxurious—and yet it may be the most important investment in your health.
