We also know that messing with our body clocks feels bad. But being awake when your body wants to sleep is also bad for you.
Studies show that people who work graveyard shifts never completely adapt to their nocturnal schedules. Those workers often have problems with high cholesterol, obesity, and diabetes. Some studies have found working overnight may even increase a person's risk of getting cancer or having a heart attack.
Here's the crazy thing: The clock that keeps you on track isn't just in your brain, but all over your body. Every cell is its own timekeeper rigged up to the SCN master clock, and all those cells have to be properly connected to the SCN to stay in sync. Blackshaw knows this because he tried disrupting the connection.
What he found in the mice was "remarkable" disruption when his team removed a key gene that helps the SCN communicate with other cells. Instead of going about their day on a normal 24-hour schedule, mice started operating as if they had two or even three body clocks governing their behavior at the same time.
"When we take a close look at their rhythms, we start to see real problems," Blackshaw said. "So the clock is still running but it's not as well synchronized. It looks like light can still synchronize their activity rhtyms. But if we put them in the dark... and just examine the core circadian oscillator, we find that it's just massively disrupted."
This matters for humans because we know that there are people out there who have altered circadian rhythms—people who are severe night owls, or those might call themselves both morning people and night owls depending on the day.
Looking more closely at a person's suprachiasmatic nucleus could also help explain why some people who work regular day-time hours develop health problems. If there's a mismatch in synchronicity between someone's master clock and the rhythms in the rest of his cells, that may be a clue that there's something bigger wrong with the SCN or its proteins.
"This tiny little structure controls many, many things," Blackshaw said. "We're talking about a very broad range of physiological processes including not only metabolism but also mood, cognitive function as well, memory, depression, and also reproduction."
All of this raises a question about all those other clocks—the rhythms in every cell that take cues from the SCN on timing. If the master clock is so important, why do we even have all those mini clocks?
Scientists aren't really sure.
But Blackshaw suspects it may be a matter of redundancy. Cell-level clocks—which can keep time without the SCN working for a matter of hours or days after a disruption—are "gyroscopic stabilizers, training wheels on a bike, actually many sets of training wheels."
But your body's clockwork may instead be something simpler and more profound. It may have to do with where all humans begin—as single cells.
"Because if you think about it, single-celled organisms like blue-green algae maintain their own clocks, too," Blackshaw said. "It could well be that the whole process starts with a single-cell oscillator, or clock, that's really baked into the cake when you start to evolve multi-cellularly. It's engineered really deep into the system."