I know evolution is governed by chance and it is random but does it make sense to “ruin” sleep if there’s light? I mean normally, outside, you never have pure darkness, there are the moon and stars even at night. In certain zones of the Earth we also have long periods of no sunshine and long periods of only sunshine.
I don’t know if my question is clear enough but I hope so.
Bonus question: are animals subject to the same contribution of light or lack of it to the quality of sleep?
A question that I’m an expert in!
I study circadian rhythms (the process that is responsible for getting us to sleep in the night). Specifically, how circadian rhythms influence how easily we catch diseases, but that part is less relevant to the question.
So since Earth rotates and has day/night cycles, life on Earth evolved to try to predict when the day and night comes. That’s what circadian rhythms do. This is really important, since day and night aren’t just associated with lightness/darkness. Day and night are associated with a ton of different environmental differences. For instance, it’s colder at night, so animals need a way of keeping warm at night. There’s more UV light at day, so animals need a way of resisting DNA damage in the day. There’s some evidence that the bacteria in the air are different at day vs. at night, so animals will need to have different levels of immune system alertness.
We as humans live in artificial houses with artificial lighting, so we can lose track of why this is really important. But if you’ve ever went camping or tried to stay out at night you’ll probably understand why it’s really important for animals to be able to predict the time.
Circadian rhythms end up getting reinforced on a community level, since if it’s easier to see in the day, an animal is more likely to forage in the day. Then predators will notice that prey is more plentiful in the day, so it will also be more likely for predators to hunt in the day as well.
Anyways, the end result of all of this is that animals have a huge evolutionary pressure to pick either the day or night to be their active period, which is the time where they look for food and in general just be awake. And whatever they don’t pick, that’s their rest period, the time where they sleep and recover.
But how do animals know that their circadian rhythms are predicting the correct time? Imagine a mouse in its burrow - it wouldn’t be able to tell what time it is just by looking at the sky. And even just stepping out for a second to check would be very dangerous if it ended up being the wrong time. Animals need a way of reading what time it is when their out and about and then correcting their circadian rhythms if the rhythm is inaccurate. There’s a lot of different measurements that animals use to read the time, but the key here is that the measurements that they pick must change significantly between day and night. In other words, it must be a very obvious signal, like “oh, I see this signal, so there is no doubt that the time is day.”
Vast majority of the time, the most obvious signal ends up behind light. And it makes sense - if you see bright light, that is the clearest indication that it is day outside. So for many animals, light is the primary measure that animals use to read the time.
So to wrap back around to your question, it’s not necessarily that light ruins sleep because evolution just decided to go “nae nae,” it’s because predicting time is incredibly important for keeping animals and humans alive, and up until very recently, light has simply been the easiest and best proxy for the time
And to answer your bonus question, yes, other animals have their sleep messed up by light too
Due to being a “night owl” myself, I guess I’ve always been a little doubtful regarding circadian rhythms myself; but your explanation did a great job of boiling it all down to the most significant component parts. Thank you! I really liked your summary!
No need to use quotation marks - it is scientifically confirmed that night owls and early birds exist (among a number of other, less-well-known circadian types). We call them chronotypes, and it’s an active field of study. Unfortunately it’s not something that I specialize in, so I can’t comment too much on it.
However, it is very well acknowledged in the field that modern society is built on an early bird schedule and that completely screws over night owls. (To my memory, night owls tend to score lower on tests, pursue higher education less than early birds, tend to be less promoted and generally less successful than early birds. Inversely, night owls tend to do better in evening classes than early birds.)
Makes sense. As a kid up until 4th grade I used to go to school in the afternoon and I used to have good grades, 5th grade onwards I started going to class very early in the morning, my grades plummeted immediately and I started to hate school.
As a fellow night owl that gets pretty deep into the late night, I’ve had the idea that it is actually good to have a small percentage of the population awake while most of the others sleep to help keep watch. I don’t have any way to prove this, but it’s something that I feel makes sense.
I’m pretty sure that’s the general hypothesis in the field, but as you might imagine, it’ll be very difficult to prove. There was a study done sometime (I don’t fully remember when) where researchers collected data on when people go to sleep and when they wake up, and they found that there was a remarkably normal distribution in the population for when people wake up and sleep.
My personal interpretation is that chronotypes (what you call early birds and night owls) are genetic in some way, but I don’t specialize in this area, so don’t take my word for it
Cats: I reject your reality and substitute my own. I’m not sure if there are any other animals that are crepuscular, but I assume there are.
Very neat write-up; thank you!
Yeah, crepuscular animals are weird. They have circadian rhythms (the circadian clock is incredibly well conserved across vertebrates and to a lesser extent, across invertebrates), but I’m not actually entirely sure how their circadian clock work to get them to wake up at dawn/dusk
You should come to the ALAN conference next year if you can.
What’s that? From googling I assume it’s the artificial light at night one ?
Yes. It gathers up people from every field working on Artificial Light At Night (ALAN) every two years. It’s always very interesting and brings forth a lot on international and interdisciplinary collaborations.
Plus, it’ll be in Ireland next year.
Sorry to piggyback onto your comment, and I know you can’t give medical advice, but I wonder if you have any insight into a problem I have with sleep.
I’m early 40s now. One of my earliest memories, aged around 4, is not being able to fall asleep. I’ve tried EVERYTHING over the years. Sleeping pills are a guarantee if things are getting squirrelly, but give me severe rebound insomnia the next day. When I do fall asleep, it’s like I can sleep for way longer than is normal (so either cause of sleep debt or poor sleep quality).
I’ve always joked that maybe I should be on a planet with a 28 hour day. But I also know that my lack of normal sleep is potentially storing up huge problems like increasing my risk of cancer, heart disease etc.
Melatonin kind of helps. But no matter what I do… My sleep pattern goes out of synch.
I’ve gone through school, ‘normal’ 9 to 5 jobs, relationships, all a big struggle as I have to perform at a normal level despite not having slept for 24+ hours fairly regularly.
I can do everything ‘right’ (no light in the evening, exercise, healthy diet, no excitement in the evening, no caffeine, mild sleep supplements) and still find myself unable to sleep. What the frick is wrong with me… Am I doomed to continue like this? I just want to sleep like a normal human being!
You’re right, I can’t give medical advice. But having abnormally long or short circadian days is a known thing - called circadian diseases. It’s not really my specialty, so I can’t comment too much on it, but my understanding is that many of them are genetic. These genetic variations can cause the circadian clock to run slower or faster than normal (which happens to be adjacent to what I study, so I can talk about it in excruciating detail if desired)
The Familial Advanced Sleep Phase Syndrome (FASP) is one such genetic circadian disease that gets a lot of attention among the circadian field, but you almost certainly don’t have it, since FASP makes your clock run shorter than 24 hours, whereas you seem to imply that yours runs longer.
The key thing to remember is that the circadian clock is not psychological. There is an actual, physical, molecular clock running in your brain and in nearly all the cells in your body. If this clock has imperfections, then that will directly lead to consequences in your circadian rhythms and your sleep cycle. The circadian clock is a real thing that people with the right equipment can measure and read. It wouldn’t even be particularly hard - just a blood sample or a swab would be sufficient. To be honest, I myself would like to study your cells to see if there really is anything out of place, but that would probably break so many research and ethics rules.
Anyways, to answer your question, I would recommend getting a medical opinion - it might be worth specifically bringing up that you suspect you have a circadian disease. I’m not too sure about treatment options, since my impression has generally been that we kind of don’t have any treatments for circadian diseases. But it’s not really my specialty, so maybe there is. My memory is that melatonin is a masking cue, which basically means that it makes you sleep but it doesn’t actually affect your circadian clock (which probably explains your poor experience with melatonin).
Thank you so much for the detailed response, I really appreciate it. Over the years I’ve looked into this a lot but you’ve given me some really useful new information!
Health care in the UK, especially for lesser known genetic diseases, can be a bit of a lottery… I moved up the country 6 months ago, and within a month had been tested & diagnosed for a generic mutation called FMF (familial Mediterranean fever). My dad / sister both have it but despite nearly a decade of requests I was unable to get a doc to investigate it. So far up here the gp response has been a referral to a website for cognitive behavioural therapy.
I’ll push on though and see if there’s anything more they can investigate. Thanks again for the info :)
I have the exact same thing.
Ever heard of
https://en.m.wikipedia.org/wiki/Delayed_sleep_phase_disorder
?
We had a community on Reddit which I kinda miss, really small there as well but I’m not going back for it.
Thanks, I do suspect I have delayed phase sleep disorder. It’s good to know I’m not alone. Do you have any coping strategies?
My coping strategy is ‘modafinil to keep me from not being a zombie when particularly sleep deprived’, and ‘zopiclone for if I have been up longer than I should and it’s early enough to push me back into normal sleep pattern’. But of course I’m very wary about doing that more than twice in a row, so it’s never enough to establish ‘normality’.
I don’t, unfortunately.
I’m a shell of a human, haven’t been properly employed for some years, never managed a “normal” schedule or any kind of routine really. I used to have a shift job, but then that became impossible to do as well. In the army I got myself a role that allowed me to shift my personal schedules quite a bit.
But yeah, no, it has ruined my life and ever since I told tve doctors I tried weed as a coping strategy (for sleeping and eating, it’s good), I can’t really get any help from the public doctors, since I live in such a backwards country that weed is still comparable to doing iv-opiates basically.
I take melatonin and zolpidem. Melatonin around midnight so it would always be the same but ambien when I go to bed.
Doesn’t really help.
If I lived ina country with less social secvurity, like the US, I probably would’ve ended up on the streets several years ago. I’d probably have killed myself or some other people by this point.
Now I’m just a wreck of a person waiting of some moronic bureaucratic bullshit while everyone else gets to have a life and I don’t.
Tbf mine might be “non-24 and not just a delayed sleep-phase”, but despite me now having actual sleep data from more than 6 months, I can’t even get the sleep studies place to accept my doctors referral there. Makes me so fking angry I’m gonna have a seizure again
I’m so, so sorry to hear this.
I feel really lucky that I get some government support because I have autism / bipolar. It’s not much, but the specific benefit I receive also allows me to do some work… and I’m also very lucky to be self employed in a field I enjoy (writing music). So I’m certainly not rich or even that comfortable, but it does allow me to morph my days and nights to suit my unnatural rhythms.
One thing I find about lack of sleep… it makes me really emotional, grumpy, increases likelihood of a depressive state. For me, it’s SO important to almost literally inject happiness. If we have a condition that takes away our happiness, it’s really crucial to create happiness in any way possible. Binge funny TV shows, go for a walk, watch some standup comedy, call a friend (not at 2am unless they’re also a night owl haha), make some art (doesn’t matter if you’re good at it), try learning a new skill, play a game, join a volunteering group. Those are my go-to activities, probably different for you.
Also, and I know it’ll sound trite, but I got into a couple of things during lockdown that made a big difference to my overall happiness; Buddhist and Stoic philosophy. I’m not a Buddhist, probably never will be. I definitely have a long way to go in applying Stoic principles. But they have really improved my life. Meditation is very hard at first but incredibly beneficial. If I could recommend a couple of books (one is an audiobook and for me was more transformative than Buddhist principles)… if you’ve never used Audible, you can sign up for a month trial and keep the audiobook you select, no charge if you cancel within 28 days.
This is really interesting, do you have more info on this to share?
Yeah, sure! This happens to be my field of research.
So I was referring to this particular paper, which unfortunately (to my knowledge) didn’t get much follow-up.
Tangentially, there is much other evidence that circadian rhythms have evolved in part to deal with differences in microbial pathogens at the day vs. at night. However, whether it’s because the composition of bacteria in the atmosphere is different, or because animals are more likely to get themselves exposed to pathogens when they’re foraging, or a mix of both, is unclear. My favorite paper that demonstrates this effect is this one, where the circadian clock affects how strongly the immune system responds to bacteria in the lungs. I’ll also include the seminal paper here that first kickstarted the idea that immunology is fundamentally circadian, although frankly I didn’t like how the paper was written. It looked at how mice responded to Salmonella infection at the day vs. at night and found a difference in immune response that then led to a difference in how severe the infection got.
Plenty to read, thanks.
I see that first paper is for tropical environments, is this also found in other parts of the world?
To my knowledge, a similar study has never been repeated with other biomes. Which is a shame, since I can almost guarantee that a similar diel cycle exists in virtually every biome.
Does this mean humans in far north climates have different methods of determinating sleep times? Because I’m originally from close to the equator and I’m the summer I’ll be awake until near midnight when at least we get some dusk, but the nightless days really screw me up
Ah, so this goes more into the nuance of what exactly determines the time of the circadian clock. It is very well documented that animals in the arctic circle still have circadian clocks even if it’s perpetual light or dark. I left out for simplicity that the level of light matters - that is to say, if there’s a time where it’s slightly dimmer and a time that’s slightly brighter, that is enough to adjust the circadian clock to the correct time. The adjustment process will be slower and weaker than usual, but it does happen.
Also, I hinted that animals do take in multiple measurements to determine the correct time, and that plays a role in this case. In general, light tends to be the measurement that animals will default to, but where light variation doesn’t exist, animals can and do utilize other measurements to determine the time. Eating (among other things) turns out to be a relatively strong signal, so circadian rhythms end up being somewhat self-reinforcing. After all, I would expect that you only eat when you’re awake.
But in general, circadian rhythms and the ways that animals adjust their rhythms to the correct time is a huge rabbithole
I’ve severe sleep problems.
I live on a quite a northern latitude. Finland, but the very southern end of it. (The Arctic circle only starts about at the most northern 1/3 of Finland)
I’ll upload two pictures, taken from the same spot at different times.
Which one is later, which is earlier? One is taken at 00.30 and one at 2.30. No peeking at the exif data before guessing.
Sunset or sunrise?
Couldn’t tell you, as we don’t really have those in the way you do.
I was wondering why it was so dark.
I used to live in. Jyväskylä. But the pictures and context you gave seem to be Uusimaa region.
I’m guessing the second one is dusk, assuming your camera didn’t flip the image. Sun goes in a circle here.
The rolling blackout curtain from Ikea is what helps me a lot (I think the “fyture” one?)
Second one is pretty exactly dusk, yeah. Or 8 minutes after, technically.
The first one is dawn. Two hours apart and apparently in the same place, more or less.
And Uusimaa would fit, yeah, but I’m in Varsinais-Suomi. Same thing latitude wise though, but dawn and dusk are two minutes earlier in Helsinki than in Turku.
Really cool, thank you!