Related previous question.

How would sleep cycles work on planets with day-night cycles greater than 48 hours or less than 6 hours? This part is primarily for wildlife that evolved there.

Native animals might still sleep in sync with the day-night cycles, but those are so long, they'd have to slow their metabolisms down to survive sleeping that long. This is sort of the context for my question Does day length determine metabolism?

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    $\begingroup$ This is a really interesting question, but I think it's two questions in one. Natural wildlife is a whole lot different than a settling human who has an innate 24 hour day/night cycle. It'd be easier to answer if you picked one. $\endgroup$
    – Halfthawed
    Commented Oct 23, 2019 at 16:11
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    $\begingroup$ As for the slow rotating worlds, remember how people sleep on Earth in polar regions: they break those long days and nights into 24-hour cycles. $\endgroup$
    – Yellow Sky
    Commented Oct 23, 2019 at 16:12
  • $\begingroup$ @Halfthawed Okay, can do, but how do I link my previous questions together? $\endgroup$
    – Aezyc
    Commented Oct 23, 2019 at 16:14
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    $\begingroup$ @Aezyc You might want to just ask two separate questions, a Part 1 and Part 2. It's not infrequently done on this site. $\endgroup$
    – Halfthawed
    Commented Oct 23, 2019 at 16:16
  • $\begingroup$ @Aezyc Likethat. (By writing text, copying a url, selecting said text and then pressing the "hyperlink" button above the edit pane, pasting the url into the dialogue box - et voila!) $\endgroup$ Commented Oct 23, 2019 at 16:30

1 Answer 1


Day length would undoubtedly have a major impact upon evolution leading to different solutions.

In worlds with very short day night cycles it might be expected that creatures would be more inclined to take short sleep breaks or be able to alternately sleep each half of their brain only becoming fully conscious when needed. It might even be possible to do away with sleep entirely. There are obviously advantages and disadvantages to this approach, but given a totally different environment the penalties might be acceptable or avoidable.

In worlds with very long day night cycles the effect would be similar to seasonality on Earth as prolonged periods of darkness would also lead to lower temperatures. In these circumstances hibernation might be a suitable strategy at night. During the day creatures might be drawn to building nests, burrows and other hideaways where they could sleep securely when they needed to or they might be able to use the strategies described for the short cycle worlds such as doing without sleep.


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