We have many ways of marking the passage of time. Saturday’s Winter Solstice, which marks not just the arbitrary beginning of a season, but also the slow return of daylight to the Northern hemisphere. Or the coming decade, as many reflect back on everything that’s happened since 2010, and prepare to mark the beginning of 2020—a completely human invention.
And of course, the clock on the wall and on our smartphones reminds us a dozen times a day of the tasks we haven’t yet accomplished, the meetings we’ve committed to, and the routines of eating, sleeping, and working that all rely at least somewhat on what time it is.
But there’s also an invisible timekeeper inside our cells, telling us when to sleep and when to wake. These are the clock genes, such as the period gene, which generates a protein known as PER that accumulates at night, and slowly disappears over the day, approximating a 24-hour cycle that drives other cellular machinery. This insight won its discoverers the 2017 Nobel Prize in Medicine and Physiology.
These clock genes don’t just say when you snooze: from the variability of our heart rates to the ebbs and flows of the immune system, we are ruled by circadian rhythms.
Erik Herzog, who studies the growing field of chronobiology at Washington University in St. Louis, explains how circadian rhythms are increasingly linked to more than our holiday jet lag or winter blues, but also asthma, prenatal health, and beyond. And he explains why the growing movement to end Daylight Savings Time isn’t just about convenience, but also saving lives.