In this episode of Modern Bodies, we explore the ancient biological clock that still governs the human body. Long before electricity, cities, and digital clocks, human life was structured by light — the rising and setting of the sun, and the changing seasons across the year.

Inside the brain, a tiny group of neurons track light levels and coordinates circadian rhythms that influence sleep, hormones, metabolism, mood, and immune function. Even small disruptions to this system can affect how we feel.

Daylight saving time may seem like a simple clock change, but it briefly pushes millions of people out of sync with a biological system that evolved over hundreds of thousands of years.

We’ll explore how humans historically lived by seasonal rhythms, why winter and spring shaped human activity in the past, and how ancient societies began marking the movement of the sun through rituals and calendars.

Because before time was mechanical, it was ecological.

And understanding that ancient relationship between humans, light, and the seasons helps explain why a one-hour shift in the clock can still throw our bodies off today.

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