[dahart]

Oh no I might have accidentally stepped on a small land mine. Circadian rhythms aren’t permanent. If they were, international travel would be impossible for humans. Circadian rhythms are defined as entrainable, meaning adjustments to the environment must change the rhythm. I might have to walk this back some day, but right now that site you linked gives me vibes of homeopathy. There’s a non-zero amount of irony in asking if individual humans identify with different animal species, isn’t there? The idea that an animal species as a whole sleeps at a given time undermines the very idea that each human is a unique snowflake, and suggests that the variation in humans that we’re talking about is not fixed, but is a product of environment, habits, behaviors, situational preferences, etc., doesn’t it? I mean we have lots and lots and lots of evidence that humans can change sleep schedule when they have to, and that preferences largely come from what we’re used to, no?

[TeMPOraL]

> Circadian rhythms aren’t permanent. If they were, international travel would be impossible for humans. Circadian rhythms are defined as entrainable, meaning adjustments to the environment must change the rhythm.

Sure. That's why I'm a night owl in every timezone.

You seem to be assuming that circadian rhythms are driven by some stable 24h/cycle oscillator, with an offset that can be changed with some effort, whether self-directed or in response to environment changes. But if that was the case, international travel would be a chore - you'd probably be back home before you finished adjusting.

The way I see it, circadian rhythms are more like the oscillator with a floating reference point, constantly adapting to environmental cues, and a stable offset that's near-impossible to change (probably genetically fixed). Under this model, international travel is easy - the body will quickly adjust the reference point to the new timezone, based on environmental cues, but the offset remains fixed. And this is what I observe - I'm a night owl in every timezone.

[dahart]

> You seem to be assuming that circadian rhythms are driven by some stable 24h/cycle oscillator, with an offset that can be changed with some effort, whether self-directed or in response to environment changes.

I don’t know how you got that out of what I said above, but FWIW, Wikipedia does say that in order to call something a Circadian rhythm, it must be a cycle of about 24 hours, and it must be resettable [1], which seems to match your assumptions about my assumptions exactly... your description appears to fit the definition of Circadian rhythm almost exactly, you’re only missing the bit about temperature compensation.

> if that was the case, international travel would be a chore - you’d probably be back home before you finished adjusting.

I totally don’t understand what you’re saying here. Jet lag is pretty well understood, no? It takes a few days to adjust, and they you’re fine. If you fly home after a day or two, yeah, you’re home before your Circadian rhythm got reset. If you stay a week or more, and you’d be fine overseas and then have to reset again when you get home. It’s widely agreed that jet lag does make international travel a bit of a chore, no?

I mostly assume that the minute people start talking about Circadian rhythms, we’re probably in the arena of pseudoscience. I’ve just noticed over time that invocations of Circadian rhythms get used incorrectly a lot to justify bogus arguments, like with daylight saving time, for example, with claims that humans can be out of sync with their rhythms for months and months. That’s not true according to Wikipedia’s definition, because Circadian rhythms must also be able to be “reset by exposure to external stimuli (such as light and heat).” [1] And the reset generally takes at most a few days for most people. [2] The ‘sleep foundation’ article above certainly loses credibility by mentioning Circadian rhythms and then launching into the ‘what’s your spirit animal’ personality quiz blogspam fad.

I don’t know what evidence there is for an offset that changes when traveling but can’t change when staying put, or that it’s genetic. Do you have links to any? There’s a metric ton of evidence that superficially seems to counter that idea, because humans adapt and change sleep schedules all the time, they respond to light therapy, etc.

Look I’m generally a night owl too, and left to my own devices I wake up late and go to sleep late. I have absolutely no doubt that it’s very difficult for some people to change though, I’m not suggesting it’s easy. But - have you ever tried camping outdoors for a week or more? It’s quite surprising to me how fast I adjust to waking up with the sun. Try it! There’s also loads of evidence that people have a hard time changing any habits, and that use of electronic screens and artificial lighting mess with our sleep schedules, and that jobs and life stress can as well. We have to rule all those effects out first before saying it can’t be changed, and those are really hard to rule out, no?

[1] https://en.wikipedia.org/wiki/Circadian_rhythm#Criteria

[2] https://nigms.nih.gov/education/fact-sheets/Pages/circadian-...

[MrDrMcCoy]

I may have some terminology off. The point of chronotypes is to sort out the what, who, and why of "morning people", "night owls" and various states between. I don't care for the animal metaphors either, and they can easily be omitted with no loss of value. As a "night owl" myself, I have anecdotally found that while I can certainly force myself to function early in the morning on a regular basis, my body never stops hating that even after years of doing so. The best times for me to get up and go to sleep are closer to 10 am and 2 am, respectively. The chronotypes system proposed here was useful in helping contextualize all that.