If humans found a habitable world and access to it, what would the effects be of a longer day to those who were subsequently born and raised there?

Is there any evidence that a longer day cycle (of say 26 hours) would have any impact on their health and specifically their life expectancy?

If there would be any noticeable variance, how many generations would it take to manifest?

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    $\begingroup$ I doubt adding two hours would change much. Peoples sleep hours already range from anywhere from 3-12+ hours. We also have locations near the poles that experience 24/7 sun or night time and people are capable of living there perfectly fine with the aid of technology. $\endgroup$
    – Shadowzee
    Jul 11, 2019 at 6:24
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    $\begingroup$ This seems like more suited to another stack. Perhaps biology? I think they would be more up to date with studies to do with that. I do know of a study that had participants put in an environment with no sunlight, so they couldn't measure time. IIRC, they gradually increased their "days" into something like 26-28 hours. However, that's 1. only going off by memory 2. I am probably missing some details 3. that was about self-induced change, not artificially imposed one. $\endgroup$
    – VLAZ
    Jul 11, 2019 at 7:01
  • $\begingroup$ In a very old National Geographic (maybe 40 years ago?) there was a story about a guy who lived for several months in a cave with all hints of the time of day removed. His wake-sleep cycle was observed to average something like 25 or 26 hours. There literally are not enough hours in the day! :^) $\endgroup$
    – puppetsock
    Jul 11, 2019 at 14:16

2 Answers 2


Its not going to have any noticeable effect, Humans can retrain their sleep cycle remarkably quickly if the period is indeed longer. Altered day length has actually been studied quite well in humans. Many humans actually default to a 25hr cycle without light cues. Human sleep cycles range from a range of 13 to 65 hours, with a median of 25 hours, 12 minutes without light. 26 hours is well withing the acceptable range for a human daily cycle.

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    $\begingroup$ Thanks guys. Had a notion of a plot where the lure of the new world could include prolonged life for the offspring and future generations, creating a big interest from the "Old Money" families back on Earth... But I don't want to go the "Fountain of Youth" because of some weird space organism route. $\endgroup$
    – Tommy
    Jul 12, 2019 at 16:11

I agree with VLAZ, that this question needs to be seen by somebody who can comment on biology. However it clearly has a social and psychological element too.

The first thing that comes to mind for me is that a 2-hour longer day may lead to people becoming irritable and/or depressed as the day is not yet done (ie., it's not time to turn in for bed yet) and there are still two hours to go. It may introduce a social expectation to stay busy for those extra 2 hours which some people may not be prepared for and may not want. While that may lead to people becoming over-tired, it may also engineer resentment towards whoever is imposing the pressure to be productive for those extra two hours.

I'm thinking about mild sleep deprivation on a daily basis that would be mitigated by plenty of sleep. However, I do know that sleep deprivation affects people quickly, and if most of the population feels this way then chances are, there is going to be an increase in the net number of arguments happening between people, people damaging relationships by being tetchy at each other when they don't mean to be, and so on. I think somebody who understands sleep cycles better than me could comment more on this.

People who need fewer hours of sleep per night may also find themselves falling out of sync than those who are happy to stay in bed for as many hours as you give them.

Advice from somebody with neurology training may also help as I suspect that the humans would adjust to the longer day so that the above no longer affected them. Whether the adjustment would come in the form of neuroplasticity - the ability to adjust to a different length of day - or evolution over many generations is another question.


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