Profile Books
AT ROCKEFELLER University in New York, there is a population of fruit flies with no sense of timing. While most members of their species lay eggs in the morning and doze in the afternoon, these mutants live out of sync with normal flies and with each other because they lack a working circadian clock.
These insects belong to Michael Young, who shared the 2017 Nobel prize in medicine for revealing the genetics of circadian rhythms. As journalist Linda Geddes observes in Chasing the Sun, most life forms depend on these rhythms to ensure the proper timing of biological functions.
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In organisms ranging from cyanobacteria to fruit flies to humans, circadian clocks are set by sunlight. This book is a first-rate primer on many aspects of the rich, nuanced relationship between the sun and life on Earth.
Some roles of light are known to every schoolchild. The sun powers photosynthesis, providing plants and animals with energy; sunlight absorbed by our skin produces vitamin D, which is essential for bone health. But our relationship with the sun is more complicated than we are led to believe in school, and Geddes is at her best when explaining these complexities in accessible terms.
The complications begin with the damage done to living systems by high-energy solar radiation. Because UV light causes mutations that can wreak havoc on gene function, some scientists believe that early cyanobacteria evolved to initiate DNA synthesis after dark. Other researchers hold that cyanobacteria needed a clock to switch on mechanisms during the day that counter the toxic side effects of their photosynthesis. The broader point, writes Geddes, is that circadian rhythms 鈥渆volved because aligning our activities with the daily light-dark cycle boosts our chances of survival鈥�.
鈥淥ur relationship with the sun is more complicated than we鈥檙e led to believe in school鈥�
And when Geddes refers to our chances of survival, she is talking about humans too. Even if we don鈥檛 have to worry about performing photosynthesis and our cells are pretty adept at fixing mangled DNA, synchronised cycles of sleep and wakefulness help drive behaviours that hold communities together.
These behavioural patterns have been augmented by our conscious observation of the sun. In the course of researching her book, Geddes went to Stonehenge in the UK to see winter solstice celebrations at the ancient stone circle. Such rituals, which she says grew from an early appreciation of the sun as a life force, represent the sort of coordinated activity needed to build henges 鈥� and cities. 鈥淔rom humanity鈥檚 very beginnings, the sun has governed both our bodies and our experience,鈥� writes Geddes.
If Young鈥檚 fruit flies vividly illustrate how chaotic the simplest communities become without temporal coordination, Stonehenge shows the sun as maker of civilisations.
Jonathon Keats is an artist and experimental philosopher
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