Remember that scene in "My Cousin Vinny" where Marisa Tomei says, "My biological clock is ticking likes this" and she starts stomping hard on the floor? When someone says that a woman's biological clock is ticking, it usually means that she actively wants to have a baby and feels time may be short. Scientists debate whether this is a real physiological response from the body as fertility decreases or if it's all in the head [source: Lewin].
While men can feel a biological clock ticking too, it's generally not with the same urgency, as their time to father a child is much longer than a woman's is to have one. At least, that was conventional wisdom. As both men and women are becoming parents at older ages, scientists have discovered that the father's age may have more to do with a child's genetic health than that of his or her mom [source: Carey].
That's just one use of the term "biological clock." Turns out that every living thing – men, women, animals, plants, insects, and algae – all have internal "body clocks" determined by a variety of biological rhythms. These physical, mental and behavioral patterns follow a predictable cycle every day, one that is determined largely by the body's response to light and dark [source: EarthSky]. So why do we have these clocks, and what do they do for us? Here are 10 facts that may surprise you.
The body clock isn't some rinky-dink Mickey Mouse watch. In fact, it's a series of clocks controlled by a single "master clock" located in the brain. The system works like this: Genes within the body include instructions for making proteins, which are produced in waves that rise and fall over the course of a day in a type of 24-hour cycle [sources: NIGMS, EarthSky].
The master clock manages these circadian rhythms using a group of roughly 20,000 nerve cells called the suprachiasmatic nuclei (SCN), located in the hypothalamus. This section of the brain sits above the optic nerve and produces the hormones that govern body temperature, hunger, sex drive and other workings of the body. The patterns created not only dictate when we eat and sleep, but also control heart rate and the production of blood cells and blood sugar. Although the genes and proteins generally determine individual rhythms, outside factors related to light and dark can also have a significant impact on how your body "tells time" [sources: NIGMS, Healthline, University of Utah].
Among the many hormones pumped through the body, the suprachiasmatic nuclei (SCN) controls the production of the one that makes people want to curl up in a ball on the nearest couch and catch a few zzzs. Melatonin is a naturally occurring chemical that helps regulate the circadian rhythm. The more of it that the body produces, the more likely you are to get sleepy [source: EarthSky].
Your melatonin production schedule varies based on light. Remember that the SCN is located just above the optic nerve, which sends information from the eyes to the brain. The less light that comes in – after the sun goes down and the sky becomes dark, for example – the more melatonin the SCN tells the brain to make [source: University of Maryland].
Some folks who suffer from sleep disorders will pop melatonin pills to help them get some rest. The effect of these supplements, which are available without a prescription and not regulated in the same way as pharmaceutical drugs, is still not clear. Experts warn that users should be careful to monitor the size and timing of doses so as not to throw off their natural body clocks [source: National Sleep Foundation].
Think about the body clock as a human version of the one on your smartphone. If you turn off the phone when you board a plane in New York and turn it back on when your flight lands in Los Angeles, you will notice that the clock automatically adjusts the time to reflect that you're now in a different zone. In the same way, your body clock will eventually adjust to the new light/dark cycle on the West Coast [source: Newitz].
Anyone who's ever suffered from jet lag knows that the shift doesn't happen right away. Your body has been trained to release melatonin at a certain time each night, and will initially continue to do so even when the optic nerve tells the brain that it's still light outside. Eventually however, and your brain will time the melatonin release to the darkness. In other words, the clock slowly rewinds itself to reflect the rising and falling of the sun and to ensure that you don't spend all of the prime California beach time snoring in your hotel room [source: Newitz].
Most American, Canadian and European timepieces spring forward every March, when the powers that be move the official time up an hour so as to allow people to make the most of daylight. Thought to be originally cooked up by Benjamin Franklin, daylight saving time took hold during World War I and became the law of (most) of the land in the U.S. in 1966. Then-President Lyndon Johnson signed legislation requiring official timekeepers to move their clocks forward an hour each spring and back an hour every fall [source: Espenak].
The problem is that no one seems to have consulted our body clocks before agreeing to this twice-a-year adjustment. Moving the time ahead an hour does a number on circadian rhythms, particularly in the days immediately after the change when the sun still comes up around the same time. If your alarm goes off at 7 a.m. the day after it springs forward, your body still thinks it's 6 a.m. Because the sun rises later in small increments, it's probably still dark out, and will remain dark for a few months. That means that your body won't shut off the melatonin faucet just yet. One study showed that people's circadian rhythms never fully adjust to daylight saving time and sleep behavior only returns to normal when we go back to regular time [source: Reinberg].
It's like the music group Bloodhound Gang says: "You and me, baby, ain't nothing but mammals." Other mammals also have rhythm-based body clocks that dictate when they rise in the morning and when they lie down for some shut-eye at night. In fact, bears depend on seasonal circadian rhythms to tell them when to hibernate for the winter and when to come out from their hiding places. Birds similarly fly south for the winter based on circadian (or circannual) rhythms that adapt to changes in temperature and the decreasing amount of sunlight per day [sources: Newitz, Quraishsi].
It isn't just mammals who keep time naturally either. Internal rhythms drive plants to open their leaves at dawn and close them at night. They also determine when flowers bloom seasonally [source: American Society of Plant Biologists].
The Salisbury Cathedral in England is said to be home to the world's oldest clock. The mechanical device's wrought iron hands are believed to have been tracking the passage of time since at least 1386. The clock survived war, fire and inattention before being rediscovered in the early 20th century and restored [source: Salisbury Cathedral].
The Salisbury Cathedral clock is but a wee whippersnapper when compared to the natural clocks that track our circadian rhythms. Scientists believe internal clocks evolved more than 3 billion years ago in cyanobacteria (what we also call blue-green algae), but they don't know exactly why it happened. Some say this was nature's way of leveling the playing field for organisms all competing for the same sources of energy. Circadian rhythms developed so that some creatures feed during the day and others do it at night. Others say the body clock evolved in algae to stagger the sludge's processes for photosynthesis—converting light into energy to be stored for later—and nitrogen fixation—in which plants convert nitrogen from the air into energy — so as not to counteract one another [source: Newitz].
Perhaps the reason for circadian rhythms in humans is simpler: They help you sleep, and sleep is good for you.
When you lay your head down and nod off to the feather ball, your body is restoring itself. That includes basic upkeep and repair like muscle growth, tissue maintenance, protein production and the release of growth hormones. Those hormones help children develop naturally — exhibit A in the case against little Johnny staying up to watch Jimmy Fallon — but also play a key role in helping adults rebuild tissue over time. In fact, it's believed that some of these functions only happen during sleep hours. Animals deprived of sleep will lose all immune function and die in just a few weeks [source: Harvard Medical School].
If you've ever popped out of bed after a nice long slumber and felt mentally refreshed, it's probably not just because you spent the night dreaming about being fanned and fed grapes by models poolside at an Italian villa. Sleep helps humans restore their mental energy and cognitive functions that often get tapped out during waking hours [source: Harvard Medical School]. Our circadian rhythms naturally make us sleepy at night.
Ever wonder why you have to fight the urge to sleep after lunch (unless you're lucky enough to work from home and can give into it)? Your body's circadian rhythm is in a natural resting place after your noontime meal. There's also another system called the sleep/wake homeostatis that tells your body when it's time to sleep, which also occurs after you've been awake for a long time. By 2 p.m., you've usually been awake for at least eight hours. Put those two systems together, alongside a heavy lunch, and it's no wonder you want to take a nap [sources: National Sleep Foundation, Korkki].
Not everyone has this feeling to the same degree but it is a natural one. In fact, for most adults, their strongest sleep drives are at 2 p.m. and 2 a.m., thanks to their circadian rhythms. However, if you got a good night's sleep, your urge to nap at lunchtime will be lessened [sources: National Sleep Foundation, Korkki].
If we've learned anything so far, it's that the body clock is wound generally to correspond to light and dark. When it starts to get dark at night, the brain tells the body it's time for a rest by releasing melatonin into the bloodstream. So, what happens when you literally flip the (light) switch in the evening?
Artificial light can send mixed signals. Yes, a small and strategically located night-light may be necessary for navigating from bedroom to bathroom when duty calls. But other lights could throw your body clock into disarray. That includes illumination coming from a television, computer or smartphone. Many people like to wind down for the night by watching the ol' boob tube -- or streaming entertainment through their computers and tablets. If you bring those devices, and the artificial light that they give off, into bed, however, you may be tricking your brain into thinking it should stay awake [source: Klein].
We've come right back to the "biological clock." Research shows that women who are pregnant or hoping to conceive should listen to their circadian rhythms and avoid artificial light at night. Sleep doesn't just help the body rejuvenate and promote growth in kids; it also protects a woman's eggs from stress. That's because melatonin is believed to have antioxidant qualities and defends the body against inflammation while stimulating the immune system, particularly during ovulation [sources: Klein, Nierenberg].
When the lights go on at night, melatonin production slows or stops. Experts say that women who are expecting should maintain steady sleep patterns that conform with the light and dark cycles going on outside. That means eight hours of darkness with little or no interruptions each night. The dark, not actual sleep, is the key. The body produces melatonin as a reaction to darkness and will continue doing so, even if you can't sleep. Among other effects, researchers have found that disruptions in this routine can lead to attention-deficit/hyperactivity disorder and autism-related disorders in young children [sources: Klein, Nierenberg].
Author and podcaster Gretchen Rubin speaks with Lisa Oz and Jill Herzig on the You Turns podcast on the four tendencies.
Author's Note: 10 Facts About Biological Rhythms
Daylight saving time is a blessing and a curse. Pushing the clocks ahead an hour come spring means that the sun will still be up when I leave my office. This, of course, allows me to continue believing that I am a real, live human being rather than some sort of hunchbacked, cave-dwelling hermit who slinks around under cover of darkness. On the other hand, it seems to take me weeks of adjustment to get out of bed on time after the change. That's because I like to get up when the sun gets up. Call me crazy, call me a damn dirty hippie, call me late to work, but it is my humble belief that alarm clocks are for quitters. If the Good Lord wanted us to get up earlier, he or she would bring the sun up accordingly.
More Great Links
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- Reinberg, Steven. "Body's Clock Never Adjusts to Daylight Saving Time," ABC News. March 23, 2015 (April 19, 2015) http://abcnews.go.com/Health/Healthday/story?id=4509150
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