On a planet similar to Earth, is is possible for all living creatures to have bioluminescence? If yes, what role would it fulfill?
What other traits would be useful in such an environment? Larger eyes? Bioluminescence camouflage? Seasonal bioluminescence? Communication?
Reproductive fitness via Fisherian runaway
Fisherian runaway is a theory of sexual selection in which traits that are initially useful as a signal of fitness become exaggerated over many generations of selection. The classic example is the elaborate ornamentation of male peacocks: tail-feathers that are not useful for flight, but useful to attract mates.
In your world, perhaps bioluminescence was used early on in the evolution of animals as a signal of reproductive fitness, and became entrenched in that role via Fisherian runaway. As the creatures diverge into different species, they would display different colours/configurations to differentiate themselves. This would explain its prevalence in animals. Following from this, plants that want to be pollinated by particular animals might develop flowering bodies that mimic the bioluminescent signals of the appropriate species.
A couple things to consider: Bioluminescence is very expensive, energy-wise. If you want to dig into hard-science, you might want to think of reasons why it, and not a less expensive means of attracting mates, became so prevalent. Perhaps it initially evolved in a creature living in a deep-sea environment? Perhaps the originating species courted/mated nocturnally? In any case, for the originating species and for extant ones, you will probably want to consider how they hide from predators. (Can they turn off their luminescence? Would they try to camouflage against a plant's bioluminescence?)
Some mushrooms glow, and here's why
I thought this was interesting because I did not realize fungi used insects to carry spores around - I thought they were strictly windblown. But apparently these fungi glow to attract beetles that carry off their spores.
I am wondering now why some flowers don't glow. The whole point of flowers is to attract insects. I bet they do, but they glow in wavelengths that are hard for us to see.
If all the plants around you are glowing and you are not, you are going to stick out. You will be a dark silhouette moving against a glowy background. Bad if you are prey trying to hide. Bad if you are predator trying to be sneaky. The answer is to glow to match your background. Prey and predator alike will want to be cryptic and in a glowy world that means glowing.
Let's get an out-there option, and envision a biosphere based on cooperative organisms working together for common purpose (a Gaia-type biosphere). Let's further assume they aren't close enough all the time to use chemical signals in every environment (although this might be an important factor). All the sub-components need to be able to understand how to coordinate complex behaviors amongst less-that-sentient species, but possibly at the command of brain-type hive mind subcomponents. The simplest-functioning components might not be much smarter than a modern industrial robot (essentially hands receiving programming and carrying out tasks). Finally, let's assume the species in this collective are highly visual.
The key to coordinating this kind of behavior? They all communicate via light. In the day on land, species can see signals in the form of light and dark spots, but at night and in the water (especially deep sea) bioluminescence becomes critical for all these species to work together and carry out the will of the Gaia-entity. Flashing each other the equivalent of barcode/QR codes, a huge amount of information can be transmitted very rapidly. This allows "primitive" species in the collective to receive complex orders and carry out sophisticated tasks without really understanding what or why.
Environmental Integration
As pointed out by Anon, bioluminescence is biologically expensive....unless you're not the one paying the bill. There are many other ways to gain bioluminescence (or an equivalent effect, as seen in Point 2).
1. Predation
The blue glaucus preys on poisonous siphonophores like the Portuguese Man-of-War and stores nematocysts from its prey in its own tissue as a defense. Likewise, Costasiella kuroshimae, also known as the "leaf sheep" or the "leaf slug," eats algae and retains the algae's chloroplasts for extra energy. Finally, poison dart frogs get their poison from their insect prey, which we know because dart frogs in captivity don't exhibit the toxicity of their wilder brethren.
In much the same way, your creatures could gain bioluminescence by taking bioluminescent chemicals or cells from the plants and/or animals they eat.
2. Chemical Absorption
Similar to 1, but not quite. Ever heard of the scaly-foot snail? Yeah, well, the outer layer of its shell is made of iron sulfides, specifically greigite and pyrite. Even more interestingly, the inner layer of its shell is made of aragonite, a fluorescent form of calcium carbonate. Aragonite is also found in the shell of various mollusks and corals, being formed by physical or biological processes.
Scorpions, platypi, and various other animals also exhibit fluorescence when exposed to UV light. In fact, fluorescent animals are actually quite common, as some curious researchers with a UV torch found. It doesn't exist in mammals, but fish, amphibians, certain arthropods, and many other species do exhibit biofluorescence.
This tells us that if nothing else, it'd be an evolutionary cinch to have most, if not all, of your alien lifeforms fluorescent (since your planet is similar to Earth). Now, this is not bioluminescence, but it's pretty dang close.
It's also more plausible, since if animals are regularly exposed to or ingest fluorescent materials, there must be an awful lot of fluorescence in the environment, they'll likely become fluorescent to better blend in. There is another reason; according to livescience.com, "Experiments with tardigrades in the Paramacrobiotus genus revealed that fluorescence protects them like a layer of sunscreen, transforming damaging UV rays into harmless blue light, according to a new study." (For more on that, click here.)
In other words, biofluorescence can protect living organisms from UV, so if the ozone layer is gone or depleted, you better believe there will be a lot of biofluorescence, and a lot of glowing to come with it. If you decide to make your planet a future Earth, with clouds of pollution and depleted ozone, that would create A) a dark environment and B) give natural selection a reason to make the world glow.
Anyway, I hope this helps!
First off, is this planet so like Earth as to have many large periods of daylight?
If so, bioluminescence in just about every lifeform would have to be a side-effect of another process necessary for life. Perhaps the light is produced as a side-effect of breaking down the molecules that have stored energy in them. (Plants also take in oxygen and breath out carbon dioxide to metabolize; it's just that in a growing plant, they take in more carbon dioxide and breath out more oxygen, and in a mature one, the processes are balanced.)
If not, it could be actually useful. Certain organisms started producing chemicals that are harmful to life. Fortunately for other lifeforms, they broke down in the presence of light. Bioluminescence enabled this and heavily favors the wavelength that does the best job -- or wavelengths, if we have an arms race going between chemicals to harm competitors and bioluminescence to break it down.
Why it happened:
Bioluminescence takes a very substantial amount of energy, relative to an Earth-like environment. To make it widespread, you need a selection pressure or something artificial.
Positive pressure: The life-form gains something. This might be pollination, blending in, or mates. Negative pressure: Being dim harms the life-form. That might be from a non-UV-stable pathogen (runaway bioweapon, perhaps). However, then you have a new problem in maintaining the survival of your problem (and virulence, and non-resistance).
Artifice: Something "sufficiently advanced" instilled this, and perhaps maintains it actively.
Accident: By handwaving conservation of energy aside, this could become a property of ATP conversion or anything else you like.
The effects:
In enclosed environments - burrows, nests - this would be mainly be useful for communication. Outside, predators would have to trick their prey, so the background light during the day may improve concealment. Complex communication, as in the chromatophores of squid, might also come up.
If the energy cost is ignored entirely, it could be weaponised - either by patterns/flashes inducing seizures, or you could go over-the-top and make it an outright beam weapon.
Glowing for a different reason:
If the environment is saturated with phosphorescence, your creatures will glow just to match the background. Predators and prey may selectively coat parts of themselves in it, although airborne creatures might try to avoid it.
Let's consider two examples:
Mitochondria is common to basically all multicellular life and uses very similar chemical pathways.
Chloroplasts in plants are another symbiotic relationship, notable because the a green photo-pigment is actually low efficiency compared to competitors, not to mention the other flaws in plant photosynthesis (cough photorespiration cough RuBisCO limitation cough). But the symbiosis was such an overwhelming advantage it could overwhelm those defects. leading the first plants to outcompete all the other dominant photosynthesizes.
So your life forms have something similar to mitochondria in gross function, allowing them to utilize oxygen efficiently, however due to a quirk of the chemistry it produces some light. There is a swath of chemiluminescent reactions to look at for inspiration, plenty of them are oxidization based. the precise reaction does not matter as much as the process getting locked in due to symbiosis just like the green pigment of photosynthesis. The downside of the side effects don't matter since the symbiosis is such an overwhelming benefit. That reaction quickly gets built on top as the function becomes essential, at which point it can't be changed. Thus you end up with another case of weird evolutionary baggage.
