Hi there, it's Matt here and welcome back to the podcast.

There is an assumption most of us carry so familiar now that we rarely question it, that sleep ought to happen in silence.

A quiet bedroom, a closed door, a pair of earplugs, if the neighbors are loud.

If the room is not perfectly still, or if we can

hear the neighbor's television, a distant siren or a partner breathing, we tend to treat it as a

problem to be solved. I would like in the course of the next half hour or so to gently

complicate that assumption because for almost the entirety of human history,

it would have been unimaginable. Take the long view for a moment.

Anatomically modern humans appear in the fossil record around 300,000 years ago, the controlled

use of fire, which turns out to be one of the most important shapers

of the ancestral sleeping environment, is documented in the archaeological record to at least 400,000

years ago. That means, for the overwhelming majority of human history, sleep happened beside the crackling of a fire,

the rustle of wind through long grass, the chorus of insects, the call of nocturnal animals.

And this part matters, the breathing and shifting of whoever else was sleeping beside you.

This is not speculation. Spend time with one of the last

remaining populations living in conditions close to our ancestral sleep ecology and a clear picture

emerges. Track the Hadza of Tanzania across more than 400 nights with careful observation of their sleep sites

and you find fire present on roughly two-thirds of those nights. Their grass hut shelters offer

essentially no acoustic barrier to the environment. The real novelty then is not sleeping with sound. The real

novelty is the modern expectation of sleeping in silence. The recent explosion of interest in white

noise and pink noise machines, which some people find faintly futuristic, is in fact something closer to the opposite.

It is a technological rediscovery of the acoustic environment our species was built to sleep inside.

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