Has anyone theorized how evolution would be affected by a different length of solar day, what were the conclusions?

The thought came from thinking about life on other planets/moons, but I'm initially thinking about it from the frame of "How would life on earth and humans specifically have evolved (or if they would have) if a day were 12 hours or 48 hours?

I imagine the actual effects on evolution and lifestyle would be extensive.

Note: this question How would the human body adjust to sleep times if we were to live in a place with different day lengths? is slightly related, but just to clarify I'm intersted in effect on evolution, not adaptation if an indivdual moved between planets.

  • $\begingroup$ Think about places like the arctic circle where there are extended periods of light and dark - that would give some idea. Many plants and animals cope well with long periods of dark, and make use of the co-occurring long days at other times of the year. $\endgroup$
    – rg255
    Commented Apr 28, 2014 at 22:11
  • $\begingroup$ True, but I think season variation relates to a different set of effects. I think things like the study of deep sea life is probably more closely related, just not easily extrapolated humans. $\endgroup$
    – jb510
    Commented Apr 28, 2014 at 23:18
  • $\begingroup$ Deep sea is another - seasonally long days and nights were just a starting point for some ideas $\endgroup$
    – rg255
    Commented Apr 29, 2014 at 6:05
  • $\begingroup$ its all about adaptation.. we might look different or we might not.. each stage of evolution is basically adapting to changes in the environment to better suit our needs.. $\endgroup$ Commented Apr 29, 2014 at 9:34
  • $\begingroup$ This question is a little broad- if you remove the evolution from the question then this is quite answerable. $\endgroup$
    Commented Apr 30, 2014 at 7:46

1 Answer 1


It depends on how different. Day length affects more than just how long the periods of light and dark are. Let's assume a very slow rotation, and a very long day, maybe 1 month light, 1 month dark. The light side would get much warmer while the dark side would get much cooler. At the border between light and dark sides, you'd expect to see powerful storms as the hot moist expanding air moved into the cooler side and had to lose moisture. Any life on a planet like this would have to adapt to surviving in both hotter and cooler temperatures. We can take this to an even worse extreme and look at a planet like uranus. Uranus's axis is tilted at 97.7 degrees, so even though it rotates, the day/night cycle is controlled by it's rotation around the sun. If the earth were tilted like this, then we would 6 months of light followed by 6 months of darkness. Life would either have to keep moving to stay in the moving temperate twilight zones or adapt to hibernate.

If we assumed a shorter day/night cycle, I think the changes would be less significant. Lets say we had a 4 hour day. ( There has to be a speed where things get thrown off the planet, but I don't think 4 hours per day is fast enough ) A 4 hour day would have 2 hours of light with 2 hours of dark. My guess is that circadian rhythms would be less important. Temperature changes from light to dark would be less significant than currently.

It's an interesting thing to think about because the Earth's day is slowly getting longer as the moon exerts a tidal force on our planet, slowing our rotation and escaping further into space, but this change is so slow I doubt it will ever become a problem for humans.

  • $\begingroup$ This answer is good, but you're focusing a lot on how the solar day would affect the environment rather than evolution of humans... or at least not extending those thoughts into evolution. Would we eat differently? forage differently? have different physical body types.. $\endgroup$
    – jb510
    Commented Aug 15, 2014 at 1:47
  • $\begingroup$ If it were bad enough we wouldn't be humans. If we had 6 months of darkness and 6 months of light almost every form of life would have to go dormant for half the year, and I don't think humans would develop in an environment like that. $\endgroup$
    – user137
    Commented Aug 15, 2014 at 2:38
  • $\begingroup$ It's an interesting thought, but animals that hibernate (bears / squirrels) are not significantly different from their non-hibernating brethren. $\endgroup$
    – jb510
    Commented Aug 15, 2014 at 2:44
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    $\begingroup$ I don't know how cold the dark side of the planet would get, but I'm pretty sure it would be far colder than any winter bears have hibernated through. Wikipedia claims that the polar night lasts about 28 days en.wikipedia.org/wiki/Polar_night , which is far shorter than 6 months. And the poles would receive heat from the rest of the planet. If half the planet were dark at any given time, the center of that darkness would get very cold. And while some plants keep photosynthesizing all winter ( conifers ) they only deal with normal nights. 6 months of darkness would challenge them. $\endgroup$
    – user137
    Commented Aug 15, 2014 at 3:11

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