How Sleeping on the Ground Reshaped the Human Mind

One of the most remarkable, yet often overlooked, shifts in our evolutionary history was not what happened when we were awake—but when we were asleep.

For millions of years, our primate ancestors slept high in the trees, perched precariously on branches or nestled in rudimentary nests. This arboreal lifestyle came with a cost: lighter, more fragmented sleep, often disrupted by the ever-present risk of falling or attack. In such an environment, entering the deep neurophysiological vulnerability of REM sleep—when muscle tone disappears and the body is effectively paralyzed—was an evolutionary liability. In short, it wasn’t safe to surrender fully to REM in the trees.

But somewhere along our evolutionary path, early humans did something extraordinary: we came down from the trees, not just by day, but by night. By sleeping on the ground—often in groups around fire—we gained something precious: safety. And with safety came the possibility for deeper, richer, and longer REM sleep.

REM sleep is not just a curious biological state; it is a source of our creativity, our emotional intelligence, and our capacity to imagine futures that do not yet exist. It is the nightly theater where the brain integrates memories, solves problems, and rehearses social scenarios. The amplification of REM sleep in humans—proportionally greater than in almost any other species—is likely no coincidence. It may have been catalyzed by that very transition to ground sleeping.

When our ancestors no longer had to remain in a constant state of vigilance during sleep, REM could flourish. And with it, so did the cognitive complexity that defines us as a species. In other words, the ground didn’t just give us rest—it gave us mind.

So the next time you lie down at night, remember: you are participating in a deeply human act, one shaped by firelight, safety, and the strange miracle of REM.

Sleep well.