Pearl Mackie hosts this episode exploring circadian rhythms within the context of the drama's setting of a sunless city. The guest is chronobiologist Herman Vinen from Southampton University, who studies biological timekeeping. The episode examines whether humans could live without natural daylight cycles.
Vinen explains that our response to information varies depending on the time of day due to an internal circadian clock. He traces the evolutionary origin of biological clocks to ancient cyanobacteria, which used them to predict daylight for photosynthesis. The primary function of a circadian clock is to anticipate environmental changes, like sunrise and sunset, before they occur. Human clocks are molecularly distinct from bacterial ones but share similarities with those in insects and fungi. Daylight synchronizes our internal body clocks, coordinating the optimal time for various biological functions. For example, many babies are born around 4 a.m., and males often experience a peak in testosterone levels around 9 a.m. The circadian clock operates by rhythmically turning genes on and off over a 24-hour period using activators and repressors.
Specialized retinal ganglion cells containing the blue-light photoreceptor melanopsin send light signals to the brain's master clock. This master clock is located in the suprachiasmatic nucleus of the hypothalamus. Without a strong light-dark cycle, this master clock weakens and fails to synchronize peripheral clocks throughout the body. Vinen cites Jurgen Aschoff's post-World War II bunker studies, where people deprived of time cues maintained rhythms, but these rhythms became desynchronized from each other. This internal desynchronization mirrors the effects experienced during jet lag or shift work.
Vinen concludes that while humans could physically live in darkness, perhaps with dietary vitamin D, the health consequences would be severe. He states that internal desynchronization leads to increased disease, including more cancer, metabolic disease, stroke, and depression. The compromise of our internal timekeeping system would have significant negative consequences for health and social coordination.
The tone is educational and explanatory, directly connecting scientific concepts to the drama's premise. The style is a clear, interview-led conversation between the host and a specialist scientist.
Listeners interested in sleep science, biology, or the real-world implications of the drama's world-building would enjoy this episode. Those seeking only narrative advancement from the fictional series might prefer to skip this explanatory talk.
