# What would the eyes of a cave-dwelling race be like?

So here's the deal:

In a D&D-fantasy-style world, the continent of Archaon is inhabited by a wide variety of elves, whose physical characteristics vary based on their dwellings. The forest elves are more agile and can camouflage with the trees; the water elves have larger lungs and can swim more easily; et cetera. Some elves, however, decided to go into the caves, and never came out. Over the course of a couple hundred thousand years they evolved. They stopped developing pigments in their skin (unnecessary), they developed larger ears (to hear burrowing creatures), and their eyes had to become more receptive to light.

This is where I'm stuck.

I've done some research into the eyes of underground creatures, looking at things such as the tapetum lucidum, but I'll confess I'm not very good with biology. So, consider the following particulars:

1. The Cave Elves live deep underground, where there is very, very little visible light
2. Most light that they do view is in the blue-green spectrum, thanks to phosphorescent mushrooms and creatures
3. They began with "standard" eyes, with a pupil, iris, etc.
4. They came to the underground by choice, perhaps due to a hostile surface that was more hospitable underground.
5. The caves of Archaon are fairly well stocked, with various plants (fungi?) and burrowing animals (such as large worms) that would provide supplies for the cave elves.
6. Most objects in the world give of a very, very weak "aura"-type energy that could be considered part of the electromagnetic spectrum

Knowing this, what are some of the most likely biological night-vision evolutions the Cave Elves might develop? I've considered a few options - cat- or owl-like eyes with the aforementioned tapetum lucidum, albino-like, solid red eyes due to not requiring pigmentation in the eyes, or just plain bigger eyes.

• I would wager that the Cave Elves might simply rely on things like echolocation and smell, and simply let their eyes atrophy over time. Some underground and cave-dwelling creatures do that, although I can't dig up anything on them at the moment. – HDE 226868 Dec 28 '15 at 22:23
• Personally I'd rather not just let their eyes vanish, because one of them happens to be a major character in the story I'm writing, and it'd be too spooky, heh. They can visit the surface, but it might be uncomfortable to their eyes. – MutantOctopus Dec 28 '15 at 22:24
• Several billion years is way way too long. The evolutionary divergence between different kinds of elves over that length of time would result in them being unrecognisable as relatives of each other -- it's the time to go from a primitive bacterium to a human being. Try a few hundred thousand years. – Mike Scott Dec 29 '15 at 15:00
• Few hundred thousand, got it, thanks. I didn't want to underestimate, after all, hehheh. – MutantOctopus Dec 29 '15 at 15:05
• I think you have a lot of lee-way. Evolution would not necessarily rid them of pigment or change their eyes. The basic tenet of evolution is that it selects for traits that are advantageous. It does not select against traits that serve no purpose. This is why we have an appendix. It serves no purpose, but it doesn't hurt us, so there's no reason for it to evolve away. That said, any positive advantage would be selected for, so the eye could get something like the tapetum lucidem you mentioned or anything that allows them to gather more light. – Jason Bray Dec 29 '15 at 20:33

Did their brain atrophy as well? It strikes me that elves overall tend to be fairly intelligent and clever compared to other beings. In the case of at least one video game, the elves were locked up in caves and thus had no option, but to evolve the most basic survival characteristics that would lend themselves to hunting, eating, fighting, etc. in the dark and thus relied on hearing and had no eyes.

If the elves lived in caves by choice and it were important for the cave elves to pass on knowledge of medicine, complex formulas, anatomy, arithmetic, etc. so as to defend themselves from the outside world, or for salvaging outside at night, then some kind of eyesight would be important for survival(cave murals/sketches).

You could always argue that the blue-green light altered the color of their pupil. Larger irises tend to be associated with letting in more light so as to see better in the dark so perhaps the iris is so dominant that the pupil can't be seen at all?

They could have two eyelids: one inner, semi-translucent, and dark eyelid that protected their eyes from any light brighter than the mushrooms(torches, lanterns, the sun), and the outer opaque fleshy eyelid.

• I doubt their brain would have atrophied. They decided to enter the caves entirely by choice. Most of their food came from underground plants and creatures, such as large burrowing worms. They probably originated from living in generally hostile outdoor environments with more hospitable undergrounds... In any case I like the two eyelids idea. It seems a nice compromise from the original solid eye color idea I had, and a more likely biological standpoint... I'll see if any other ideas come in but this looks pretty well accepted. Thanks. :) – MutantOctopus Dec 29 '15 at 5:50
• Of course, happy to help! – Eric Dec 29 '15 at 15:02

They probably wouldn't be blind/eyeless, since there is light from fungus and creatures.
Also, unlike a cave fish, they would probably at times go to the surface just to see what is happening, maybe even do some trading.

Unless they were down in the caves for a very very long time there wouldn't be time for things like larger eyes and ears to develop, but they don't really need to. Most fantasy elves already have exceptional hearing and vision, dark adapted eyes can see a lot in fairly low light, and faint sounds in a silent cave would be magnified.
Being intelligent, they might even use light sources like phosphorescent stuff in a lantern, fire fueled by oil harvested from cave worms, or even elfin magic; A light in the darkness when all other lights go out.

One thing that might happen is a sensitivity to the aura around them, used like a kind of sonar.

• Well the thing is they already have been underground for quite some time. The elves of this world might have good hearing but not exceptional dark-vision, though they do have sharp eyes, and when they were first created they hadn't yet discovered magic. As time plowed on they went deeper and deeper, and most communities would have appointed specific people to go to the surface. – MutantOctopus Dec 29 '15 at 15:05
• @BHustus Your question didn't really specify how long they had been down there. IIRC it takes many generations to breed traits like that in, though it is possible. Look what we did to dogs. Elves with better vision and hearing would be seen as more capable, and so would make them more sought out as mates, passing those traits on. My point was that they would be more like bats than cave fish. There is still a use for eyes, even if other senses are more useful down in the deep dark. And being intelligent, they would find ways to make things easier, like plant more glowing moss in traveled areas. – AndyD273 Dec 29 '15 at 15:14
• I see now where you did put a time frame, and in the comments where you are talking about it. My appologies for missing it. That being said, I'll stick to the rest of my answer. We've been domesticating and breeding dogs for tens of thousands of years at least, and genetically they are essentially the same as wolves. Also, with less radiation underground, genetic mutations should be slower than on the surface, unless the cave has a radiation source. – AndyD273 Dec 29 '15 at 15:19
• Radiation? That's a factor I didn't consider... Interesting. I'll have to consider that. I was always running under the idea that the elves were a race particularly suited to evolution and genetic "mix-ins", though I never did mention that admittedly. Thanks anyway. :) – MutantOctopus Dec 29 '15 at 15:32
• @AndyD273: From the Wikipedia page about Radon (emphasis by me) "It is often the single largest contributor to an individual's background radiation dose, and is the most variable from location to location. Despite its short lifetime, some radon gas from natural sources can accumulate to far higher than normal concentrations in buildings, especially in low areas such as basements and crawl spaces due to its heavy nature. It can also be found in some spring waters and hot springs." – celtschk Dec 29 '15 at 15:53

In one of my less detailed ideas, 200 A.D., humans in Scandinavia began living underground amongst luminous stones, producing enough light to prevent the total loss of their eyes, and they occasionally did hunt on the surface.

Their eyes, when underground, are similar to ours but with comparably big pupils, and irises so large that they remove the whites from view most of the time.

Above ground, their pupils shriveled until it almost seemed that their eyes were just irises and a small amount of whites.

In the case of these dwarves, however, some other factor (implied to be a chemical effect of the stones's presence) gave them further mutations as well, leaving it unclear whether the mutation was an effect of the stones or just natural.

My point with adding that last detail is that you should consider how their surroundings could cause mutations in their genes. You said there are glowing fungi and burrowing creatures for them to consume, so their diet is one thing that could have an extreme effect on their bodies and assist in bringing out useful chthonic evolutions.

• Chthonic? That's a new word. I'll have to use that sometime, heh heh. Anyway, that seems like a fairly good idea. And the idea of the pupils being so tiny as to basically be invisible sounds like it would work fairly well for the design I originally had; unfortunately Eric above already suggested it, but that said - you're making me reconsider it. Anyway yes, I'll consider the diets and etc. Thanks. :) – MutantOctopus Dec 30 '15 at 18:41