"Realistic" Dwarfs Part One: Bioluminescence for active Vision

Question

I've been thinking about dwarfs and their depiction in classical fantasy for while now and concluded that I find it unrealistic and lazy. Some research showed me that the current fantasy dwarfs have their roots in the christian interpretation of norse legends about lesser earth spirits or ironically dark elves. Thus I decided to design my own dwarfs and stick to an earth spirits and subterranean creature theme without sacrificing many if the iconic dwarven features. My design is ready so far, yet it has some points which may or may not be issues. So I came here to hear some opinions on my dwarfs.

This will be the first question in a series of five, which I'll all like below once they are asked.

1 Bioluminescence for active vision

2 Mesothermic and regulateable metabolism

3 Finding caves

4 Evolutionary pressures

5 Beards must remain

THE DWARVES

As the first world was shattered into many spheres of existance a group of early hominids was displaced to a dark and hostile place where they could only survive underground. They adapted in many ways. Their noses and ears grew as the associated senses shaped. They grew smaller and more muscular to navigate the caves quicker. Their metabolism turned mesothermic and they gained control over it, allowing them to hibernate or lay low in times of famine ir to eat plenty to boost their strength and vitality. Unlike other subterranean creatures however they did not loose their eyesight. Instead their eyes grew bigger and incredibly light sensitive, so light-sensitive that they later developed nictitating membranes as a form of biological sunglasses to go to the upper-world. They illuminate their surroundings with their bioluminescent skin. This makes their skin blue and if they are exposed to sunlight it turns almost black, in the darjest caverns they have an very light blue taint. They do not glow very bright, in fact only their very sensetive vision allows them to use their light.

Question

Does this kind if active sense of vision make sense for the dwarfs as subterranean critters and how exactly does it work? What is the optimal mechanism as there are two possibilities according to Wikipedia?

In some animals, the light is bacteriogenic, produced by symbiotic organisms such as Vibrio bacteria; in others, it is autogenic, produced by the animals themselves.

Is this the most practical approach to them having cave-nightvision or is there anything better I missed.

Answer 1

Is this the most practical approach to them having cave-nightvision or is there anything better I missed.

No. If you want practical, as in, 'reasonable to develop', bioluminescent skin combined with super-eyes isn't up there on the evolution list. Two reasons. First, it's two complicated systems, one of which isn't common among humanoids (the bioluminescence). Second, because glowing in the dark is a horrible idea from an evolutionary standpoint. Glow in the dark dwarves are targets for hook horrors, driders, svirfneblin, and all the other presumably horrifying fantasy races down there.

If you want practical, you want echolocation. Don't bother trying to see, just listen to them instead. Instead of evolving two systems in tandem, all it takes are much better ears, and you're good to go. The ears don't even need to be externally large (dolpins manage fine).

If you mean practical as in 'best thing to have', thermal vision is better, just have them learn to see in the infrared spectrum, and you're good to go. Maybe. Hot-blooded animals can't have it, it's only available to cold-bloods (like snakes), but your mesothermic dwarves might make the cut - if you play around with their biology a bit.

Answer 2

Bioluminescent land animals are rare in our world. There is some research to suggest that this is because the process of creating luminescence has toxic by-products. These are easily washed away in a marine setting, where the majority of bioluminescent creatures live, but are more likely to harm the carrier in a terrestrial setting. You can get around this by making your dwarves immune to this type of toxicity. However, the same article suggests that most of the terrestrial bioluminescent species, mostly beetles and millipedes, evolved this skill not to improve vision, but as a defense mechanism; the light both produces a toxic film on the creature, and warns predators of that toxicity. It is hard to imagine a hominid-type species, which would probably be the largest thing in the underground world, evolving bioluminescence for this reason. I could find no examples of terrestrial animals who are believed to have developed their bioluminesence for the purposes of vision.

If you are dead-set on bioluminescent dwarves, you might want to give them some kind of underground predator that is vulnerable to the toxic by-products of the luminescence. This would create the evolutionary pressure to develop this attribute. Given this, autogenic bioluminescence would make more sense, since it unlikely that they would share a predator with a bacteria such that a symbiotic relationship would form.

Answer 3

Since Dwarves live way underground, and assuming the temperature there is sufficiently warm to hot, how about thermal vision aka eyes that can perceive infrared light. Any form of active sense that requires you to generate either light or sound is bad because it can be backtracked to the source. Of course you can make the dwarves very sensitive to vibrations through touch. The heat-detecting vision and vibration sense will also help nicely with the lore that dwarves are good blacksmiths.

Answer 4

Having bioluminescent skin has several drawbacks:

Problem 1: As a previous poster has noted, you would need to go naked to see better.

@ 1: The problem could be reduced if instead of glowing skin the dwarves had light organs emitting concentrated light, like deep-sea fishes have. Better yet if they could direct the beam like a flashlight. The best way would be to have such organs actually built into their eyeballs, so they would swivel together to shine exactly where the dwarf is looking. Naturally they would have to be thoroughly shielded from the sensing part of the eye. As a bonus, the (relatively) intense beam could let you dazzle attackers. But it would be metabolically costly.

Problem 2: The luminescent dwarves can only see nearby, because the intensity of illumination drops of as the square of distance. But other creatures can see them from far off, a major disadvantage. It's like going through a dark forest with a lantern: sure you can see enough to avoid bumping into trees, but your lantern is visible from much farther, while blinding you to everything outside its meager circle of light.

This problem is shared by any active sense, sonar, radar, thermovision relying on illumination by IR diodes, etc. In RL, some moths can hear bat echolocation and react by dropping, but they are prey species. Imagine the disaster to bats if a predator (an owl?) evolved to hear bat pings. And there are missiles that home in on a fighter's radar ping.

@ 2: The only solution is to use a passive sense, like the overwhelming majority of Earth's biosphere does. A passive sense is stealthy, and cheap metabolically. So I recommend that you make the cave walls glow, instead of the dwarves' skin. Maybe there is an ubiquitous glowing fungus that feeds on rock whenever it is in contact with air; there are such things on Earth, but they are rare and need specific kinds of rock. Perhaps in your world they would be everywhere, and eat (slowly etch) any kind of rock. Maybe there is no fungus, but rocks naturally glow when exposed to air, through the humoral reaction of the Earth and Air elements; the glow slowly fades, but can be refreshed by scraping off the outer layer of the rock.

And if you still want glowing dwarves, because they're cool, no problem: they could be glowing to camouflage them against the glowing cave walls! ;-)