Your body runs an internal clock that keeps roughly a daily cycle even in constant darkness.

What it means

Volunteers isolated from daylight and clocks settle into a cycle a little longer than twenty four hours, which shows the rhythm is generated internally rather than driven by the sun. Light resets it each morning through a set of receptors in the eye that have nothing to do with vision. Almost every tissue carries its own clock, coordinated by one master timer in the brain.

The claim comes from NIGMS, and the page it comes from was read on 2026-08-27 to confirm it still says this.

This is not the kind of claim that goes out of date, which is why it was set as a puzzle rather than a fact with a shelf life.

Solve it yourself

This fact is a cryptogram here: 76 letters over 19 different ones, graded medium.

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Nearby in the collection

The facts either side of this one.

• NCBI Bookshelfeasy, 75 letters
• NCBI Bookshelfeasy, 77 letters
• National Human Genome Research Institutemedium, 74 letters
• National Human Genome Research Institutehard, 67 letters

About as hard as this one

Scored closest to it by the model behind our guide to solving cryptograms.

• NCBI Bookshelfmedium, 77 letters
• Royal Society of Chemistrymedium, 78 letters
• PLOS Biologymedium, 75 letters
• MedlinePlusmedium, 68 letters