The big unanswered question: the lunar timer

Kristin states her central goal: identify the inner lunar calendar and its relation to human monthly timing.

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People have long told stories about the moon’s power, from werewolves shapeshifting by the moon, to the belief that drinking water soaked with moonlight could help women conceive. And monthly rhythms appear across nature, from corals and cacti to gorillas.

But while there's lots of research showing that the daily cycles of the sun are crucial for biology, scientists have largely ignored the role of the moon – or dismissed it as pseudoscience, particularly in humans. That’s partly because there hasn’t been a convincing mechanism for how the moon might influence life on Earth - which is what my guest this week, Kristin Tessmar-Raible of the University of Vienna, is working to uncover. She studies lunar timing in marine bristleworms: four-eyed, many-legged creatures that swarm according to the phase of the moon and have light receptors buried in their brains.

Forget biological clocks, this is a biological calendar. And the fascinating thing is, she’s uncovering surprising parallels with human biology, which means what’s happening in the worms could help to reveal our own deep connection with the moon, from fertility to sleep to mental health. Jo and Kristin discuss just how far-reaching the moon’s influence may be, the colleagues who once thought she was crazy, and what it takes to change minds in science.

Kristin's home page

https://neurodevbio.univie.ac.at/tessmar-raible-research/

2024 review by Kristin & Andrés Ritter on lunar timing in biology

https://www.embopress.org/doi/full/10.1038/s44319-024-00196-5

Excerpt from Jo's book The Human Cosmos about the moon's influence on biology

https://www.wired.com/story/oysters-that-knew-what-time-it-was/

2021 study on lunar rhythms in women's menstrual cycles

https://www.science.org/doi/full/10.1126/sciadv.abe1358

2025 study on effect of LEDs and smartphones on timing of women's menstrual cycles

https://www.science.org/doi/full/10.1126/sciadv.adw4096

2024 review of links between lunar cycles, sleep and mental health

https://www.pnas.org/doi/abs/10.1073/pnas.2214756121