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I am working on a speculative evolution project at the moment that has a low atmospheric scale. As a result, the ground is almost always covered in fog or cloud-like fog that is universal across numerous humid biomes. A small minority of the year will see a reduction to this fog. Visibility can vary from a light mist to a dense fog, with somewhere in between being the average.

Fog reduces visibility, as anybody who went outside while it was foggy would know. An animal with poor vision could not hunt or forage in those conditions without specific adaptations for it. So, I am inquiring about what types of eye adaptations would help an animal in vision-impaired conditions such as this. The specialization of any recommended adaptations shouldn't be a concern as my basic reference are slug eyes.

Some quick things I would like to mention:

  • I do not want the animals to hibernate for the entire year until it isn't cloudy. I feel it would be inevitable for an ecological niche of animals that adapt to living in the fog. After all, nocturnal animals exist.
  • I do not want the animals to be blind. Some blind animals are fine but I would like to see more creative solutions. These animals are unlikely to devolve their eyes, which are their best source of sensory stimuli, in favor of evolving borderline non-existent sensory systems.

I appreciate scientific accuracy, but it is not a chain here. So, the question at hand is "What type of eyes are best suited towards constant ground-level fog and cloud cover?"

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  • $\begingroup$ Did you notice you were Asking about the nature of light, far and away above the nature of eyes? Don't most eyes perceive light through brightness, colour and resolution? To see through fog or cloud, you would most obviously need infra-red or ultra-violet vision… which some critters already have. If scientific accuracy isn't "a chain" - whatever that means - why not ignore IR or UV or both, and simply give your critters the gift of what eyes they need? $\endgroup$
    – Robbie Goodwin
    Jul 10, 2022 at 20:24
  • $\begingroup$ @RobbieGoodwin Maybe I am tired, but I can't quite understand what you are asking here. Why in the world would I ignore IR or UV? I said "scientific accuracy isn't a chain" as in, "do not let scientific accuracy dampen your creativity here." If I could just give them the eyes they need with no explanation, then why should anybody on this site ask questions when they could just have centaurs without explaining how they work or have dragons without considering how they fly? As for the rest of the question, please rephrase what you are asking. $\endgroup$
    – King of the Hounds
    Jul 11, 2022 at 0:25
  • $\begingroup$ Then why let scientific accuracy dampen your creativity here? If you want eyes that see through cloud, that will most likely be IR, though UV might do it. Beyond that, how are you not in the realm of magic? $\endgroup$
    – Robbie Goodwin
    Jul 11, 2022 at 22:39
  • $\begingroup$ @RobbieGoodwin Because I want some scientific accuracy, it's a speculative evolution project. I asked this question specifically because I was unsure what type of eyes would see through fog. And would you care to highlight where I said there is magic involved in this specevo project? There isn't a wisp of magic in the project since it is science fiction, nor do I want to add magic to accommodate a simple enough adaptation to vision. $\endgroup$
    – King of the Hounds
    Jul 11, 2022 at 23:48

4 Answers 4

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Long wavelengths scatter least.

I was once approaching a stoplight in dense fog. It was red. Then it disappeared. When I got closer I could see it had turned green. The green light was scattered by the fog but the red light could get through. That is also why sunsets are red. The longest wavelengths make it through the intervening air while scattering least. Shorter wavelengths are lost to scatter.

Unscattered light carries with it information about things it has reflected off. Eyes adapted to see in red and infrared would work the best.

As far as eyes go, maybe the best vision would not be an eye. The pit organs that some snakes use to see heat (far infrared radiation) are not eyes and have no analog in other vertebrates. A radiation detecting organ like the pit vipers pit could be superior to eyes in an environment where shorter wavelength radiation is scattered.

Example: here smoke stands in for fog. Visible light is scattered but the infrared comes right through and is seen by the thermal camera.

H4 Thermal Camera Line | Smoke Test | Part 2

thermal camera thru fog

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    $\begingroup$ Thanks for this answer! I will wait to accept it so that other people can contribute but you'll most likely be the accepted answer. I hadn't considered the use of infrared to see through clouds and fog. $\endgroup$
    – King of the Hounds
    Jul 10, 2022 at 1:59
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    $\begingroup$ Could not the pits form proper eyes with time, or would the longer wavelengths of infrared interfere with the development of a pinhole? $\endgroup$
    – No Name
    Jul 10, 2022 at 18:44
  • $\begingroup$ Many animals can see deeper into the infra-red spectrum (also ultra-violet) than we can with their eyes. Pit vipers may be the best (among vertebrates), but there are plenty of animals with a wider spectrum than ours but less than pit vipers. Among invertebrates, there's even more. $\endgroup$
    – Darrel Hoffman
    Jul 11, 2022 at 18:14
  • $\begingroup$ Depending on the makeup of the fog, this may not be as effective as the pictured example. Water vapor fog degrades the effectiveness of thermal vision dramatically compared to smoke. Dense fogs or heavy precipitation bring detection ranges down to visible light spectrum in some conditions. So even without the fog totally clearing you can have somewhat "clear sky" and "cloudy" days with variations in the density of the fog to those with thermal vision. The term "greenhouse gasses" usually refer to a group of gasses that are opaque in parts of the thermal spectrum. $\endgroup$
    – David S
    Jul 11, 2022 at 18:49
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Under such conditions it might be better for animals to have a preference for using echo location (bats) or enhanced hearing (some owls). More useful information can be obtained via sound from one's environment when vision is of limited value.

The trouble with a foggy environment is daylight can be bright but vision is obscured by an opaque atmosphere. I initially thought animals might have eyes similar to what nocturnal animals have to compensate for low light levels but a foggy atmosphere may not be dim, just opaque.

As the other answer states, eyes developed to process longer wavelength light (red and infrared) would be better.

A higher developed sense of smell would also assist animals.

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    $\begingroup$ Thanks for your answer! I failed to consider that a foggy environment wouldn't necessarily be dark, but the fact that it is bright makes my life infinitely easier for evolving plants. One question however, wouldn't the fog limit the radius of smell for animals? I assumed that a humid fog would limit the use of smell, since chemicals that create smells would end up trapped in the suspended water droplets. $\endgroup$
    – King of the Hounds
    Jul 10, 2022 at 16:19
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    $\begingroup$ That would depend on the nature of the aroma/scent, whether its oil or water soluble. For smells arising from water soluble chemicals the range may well be limited. $\endgroup$
    – user81881
    Jul 10, 2022 at 16:42
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    $\begingroup$ There's also the fact that fog dampens (hah) sound. Really foggy days can be eerily quiet, and not just because the birds aren't singing $\endgroup$
    – No Name
    Jul 10, 2022 at 18:42
  • $\begingroup$ @NoName Interesting! I never thought of the idea that fog could dampen sounds, but it makes sense when I think about it further. It's odd to think about how fog hinders all the senses, not just vision. $\endgroup$
    – King of the Hounds
    Jul 11, 2022 at 0:29
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Consider adding polarization to the long wavelength vision mentioned above.

Polarization can be used to reduce the effects of scattering. You combine images made with different polarization with some tricky processing to get much better contrast.

Animal brains already do a lot of processing to combine the images from two eyes to a stereo view. Give the critters eyes that are polarized differently, and a somewhat larger visual cortex to do the processing.

Besides the improved contrast, your critters will gain the ability to detect the sun even through heavy fog using the sunstone effect.

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  • $\begingroup$ This is an interesting mention. While I have heard of infrared and the like mentioned above, I've never heard of the sunstone effect or polarization. Despite that, this is very useful information that I'll use alongside the other answers, thank you for taking time to respond! $\endgroup$
    – King of the Hounds
    Jul 11, 2022 at 14:32
  • $\begingroup$ @jre - silly question; could that relieve Rayleigh scattering for improved resolution at range? (elf-sight, you might say) $\endgroup$
    – Peter Wone
    Jul 12, 2022 at 2:35
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Our own environment is foggy. Atmospheric scattering of EM radiation known as Rayleigh Scattering begins with blue and becomes more pronounced as frequency rises. This is why the visible spectrum is where it is. Any lower would lack resolution at range, any higher would lack range.

The world you describe will be without meaningful distance vision. In the absence of distance vision, visual apparatus will be more strongly driven by factors other than focus. Omnidirectional motion sense, for example, is better served by faceted insect eyes. They can't see worth a damn past a metre but sneaking up on them requires very slow movement till the hunter is in range, then very fast movement like a frog's tongue.

Or set traps like spiderweb (sometimes a snare, sometimes a telltale).

But my answer is that non focal motion sensing eyes are best adapted to the conditions you describe.

Ooh, I forgot about polarisation as mentioned by another answer. That will partly solve the scattering problem. And it's entirely evolvable — slitted pupils, for starters. While that won't give you distance vision as we know it, it would certainly be a survival edge.

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