If you’ve ever tried apartment living, you probably know the feeling. It’s 11:30 at night, and the guy who lives above you has decided that this is the best time to schedule his Iron Maiden cover band practice. Or maybe you’re the guy in the band, and you’re sick and tired of the stuck-up dude downstairs stomping around and grinding coffee at the crack of dawn, when all decent headbangers are sleeping. Turns out that there’s a very good reason both of these people hate each other, and it’s all about the clocks hardwired into their genes.
In the world of sleep studies, there are “night owls” (people who are in bed after 11 p.m. and awake after 8 a.m.) and “larks” (the mythological creatures who get up before 8, even on the weekends). There are lots of studies about how the two different sleep schedules make for different brain types, but not a lot about what made them different in the first place. But according to a study published in Nature in 2016, a difference in circadian rhythms might be written into your genes.
The study was a genome-wide association study (also known as a GWAS) using the DNA of nearly 90,000 people who had submitted their genetic material to 23andMe. The researchers discovered 15 genetic patterns that tended to be associated with being a lark. Some of those patterns lay close to patterns we know to determine circadian rhythms, and others lay near genes responsible for the eyes detecting light. The evidence is pretty clear: If you tend to wake up early, it’s probably because your genes are telling you so.
It’s important to remember, however, that the circadian rhythm of an individual rarely stays static for that person’s entire life. Besides your genes, there’s a lot that determines exactly when you get sleepy and how much rest you need. Very broadly speaking, men tend to be night owls and women tend to be larks, and age plays a pretty major role in your rhythm as well. School-age kids lean towards lark-dom, while teenagers are notorious owls. Many adults transition back into larks as they grow older, but others will remain late-risers their entire life. In fact, there may be an evolutionary reason your bedtime drifts earlier as you age.
The jury is still out on if it’s better to be up early or late (the TL;DR version is night owls are smarter but more depressed, and larks are happier but not necessarily healthier), but either way, you’ll probably end up at both extremes at one point in your life.
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