We Have No Idea Why

Check out our shiny new story-based merch at dftba.com/minu...
Most animals on earth are bioluminescent, but almost all of them live in the ocean - and scientists aren’t sure why.
LEARN MORE
**************
To learn more about this topic, start your googling with these keywords:
- Bioluminescence: the biochemical emission of light by living organisms such as fireflies and deep-sea fishes.
- Biofluorescence: The emission of previously absorbed light by fluorescent proteins in a living organism.
- Luciferin: an organic substance, present in luminescent organisms such as fireflies, that produces light when oxidized by the action of the enzyme luciferase.
SUPPORT MINUTEEARTH
**************************
If you like what we do, you can help us!:
- Become our patron: / minuteearth
- Share this video with your friends and family
- Leave us a comment (we read them!)
CREDITS
*********
Cameron Duke | Script Writer, Narrator and Director
Sarah Berman | Illustration, Video Editing and Animation
Aldo de Vos | Music
MinuteEarth is produced by Neptune Studios LLC
neptunestudios...
OUR STAFF
************
Lizah van der Aart • Sarah Berman • Cameron Duke
Arcadi Garcia i Rius • David Goldenberg • Melissa Hayes
Alex Reich • Henry Reich • Peter Reich
Ever Salazar • Leonardo Souza • Kate Yoshida
OUR LINKS
************
Merch | dftba.com/minut...
MinuteEarth Explains Book | minuteearth.co...
KZbin | / minuteearth
TikTok | / minuteearth
Twitter | / minuteearth
Instagram | / minute_earth
Facebook | / minuteearth
Website | minuteearth.com
Apple Podcasts| podcasts.apple...
REFERENCES
**************
Belkin, S. Bioluminescence Fundamentals and Applications in Biotechnology - Volume 1. Berlin Heidelberg, Springer-Verlag GmbH, 2014.Davis, Matthew P., et al. “Repeated and Widespread Evolution of Bioluminescence in Marine Fishes.” PLOS ONE, vol. 11, no. 6, 8 June 2016, p. e0155154, doi.org/10.137...
Delroisse, Jérôme, et al. “Leaving the Dark Side? Insights into the Evolution of Luciferases.” Frontiers in Marine Science, vol. 8, 30 June 2021, doi.org/10.338...
Griffiths, Mansel W. “ATP BIOLUMINESCENCE | Application in Hygiene Monitoring.” Encyclopedia of Food Microbiology, 1999, pp. 94-101, doi.org/10.100...
Haddock, Steven. Senior Scientist, Monterrey Bay Aquarium - Personal Communication.
Hellinger, Jens, et al. “The Flashlight Fish Anomalops Katoptron Uses Bioluminescent Light to Detect Prey in the Dark.” PLOS ONE, vol. 12, no. 2, 8 Feb. 2017, p. e0170489, doi.org/10.137...
Marek, Paul, et al. “Bioluminescent Aposematism in Millipedes.” Current Biology, vol. 21, no. 18, Sept. 2011, pp. R680-R681, doi.org/10.101...
Martini, Séverine, et al. “Distribution and Quantification of Bioluminescence as an Ecological Trait in the Deep Sea Benthos.” Scientific Reports, vol. 9, no. 1, 10 Oct. 2019, doi.org/10.103...
Martini, Séverine, and Steven H. D. Haddock. “Quantification of Bioluminescence from the Surface to the Deep Sea Demonstrates Its Predominance as an Ecological Trait.” Scientific Reports, vol. 7, no. 1, 4 Apr. 2017, doi.org/10.103...
Mofford, David M., et al. “Latent Luciferase Activity in the Fruit Fly Revealed by a Synthetic Luciferin.” Proceedings of the National Academy of Sciences, vol. 111, no. 12, 10 Mar. 2014, pp. 4443-4448, doi.org/10.107...
Yirka, Bob. “Researchers Seek to Explain Why There Are so Few Land Dwelling Bioluminescent Species.” Phys.org, Phys.org, 23 Aug. 2012, phys.org/news/...

[@12tone]

I'm no expert, so it's very possible I'm missing something, but it seems like there'd be a significant difference between nocturnal/polar darkness levels and deep-sea darkness levels. Most nocturnal animals can adapt to lower light levels by simply improving their night vision, but at some point, that'd probably start showing diminishing returns, and when you get deep enough in the ocean the level of darkness could be high enough that those sorts of adaptations wouldn't really work, forcing other approaches. That doesn't necessarily answer all of the problem (I assume I'm not the first person to think of that, after all) but it feels like it'd at least go a long way toward starting to explain the discrepancy, right?

[@MinuteEarth]

There's definitely a difference between deep-sea darkness and the polar darkness, but one fascinating thing (in my opinon) that we didn't include in the video is that the rate of bioluminescent species is more or less consistent from the surface down to 3900 meters (which is how deep the authors of this paper surveyed: www.nature.com/articles/srep45750#:~:text=Our%20study%20quantifies%20that%2076,a%203%2C900%2Dmeter%20depth%20range) So many of bioluminescent ocean species experience both day and night (or live in a somewhat twilight-zone depth)

[@edythebeast7087]

Hey they answered

[@indeecjo]

Good point, but what about cave dwellers some live in places without any light

[@erictheepic5019]

@@MinuteEarth Well if bioluminescence does preferentially evolve in the depths, that might provide an easy 'in' for the descendants of a bioluminescent species to return to the surface and have the benefits of bioluminescence there too, even if the benefits are weaker. However, this still doesn't make any sense under the additional context of places like Lake Baikal lacking bioluminescence. I guess there's an interesting question that might help answer the mystery: Has any species devolved bioluminescence? If so, that might be illuminating, or maybe we'll still be left in the dark.

[@WanderTheNomad]

@@MinuteEarth what are the chemical/evolutionary precursors to bioluminescence? Or basically, how did it come to be/what led up to it?

[@ordinaryorca9334]

I think necessity plays an important role. To find a mate on land animals use flashy colours or pheromones but smelling is much more difficult in the ocean, sight is useless at great depths and taste is useless in general. Meaning animals need to specialise their hearing (echolocation), sight or create a new sense (electroreception). Using bioluminescence allows you to use your existing senses without upgrading them to their extremes. It is also very versatile such as finding mates or prey and even as a defense. This versatility means that many pressures can lead you down this path explaining in part why they love it so much.

[@wasd____]

Smelling is actually much easier in the ocean. Chemicals can remain suspended in water much better than in air.

[@the_undead]

Smelling is actually much easier in the ocean than it is on land because currents can you usually keep assent much more concentrated for much longer distances than wind, site is absolutely useful in the dark because of all the bioluminescence that the vast majority of creatures down there use Also I have no idea why this person said we don't know why so many creatures in the ocean use bioluminescence (or however they worded it) because with the release of blue planet 1 in the early 2000s, it was actually known why so many different species used it, some for hunting others for communication and still more for distracting predators were the main three reasons.

[@mahadevparmekar2565]

@@wasd____ Smelling isn't about 'suspending particles'. Its about using volatile compounds that evaporate at room temperatures and disperse in the air. This mechanism wouldn't work in water. The only molecules that remain suspended in water are the ones that are soluble in water or have similar density to water. (Otherwise they would float or sink quickly).

[@mahadevparmekar2565]

I also made a similar comment earlier. Its not that land animals cannot evolve bioluminescence. The main issue is that land animals have a better alternative, that is smell. Smell is more efficient, takes less energy (than bioluminescence- light production is every energy intensive), and smell can be used for multiple other purposes. That also explains why we have flowers instead of bioluminescent plants to attract insects for pollination. (Although pretty much every insect is attracted to light). We humans are visual creatures so we take smell for granted. Nearly 90% land species use smell as their primary sense. Including dogs and other non-primate mammals. Despite sight being such an important sense, the fact that overwhelming terrestrial species use smell as the primary sense, speaks volumes about how effective smell is. Ocean creatures have evolved various strategies to combat lack of smell. Bioluminescence, echo-location, are just some examples.

[@the_undead]

@@mahadevparmekar2565 if smell is so worthless in the ocean then why the hell do sharks rely on it about as much as a lot of land predators? Also there is at least one species of fish down in the deep that does use scent for something, female angler fish release sense into the water that male angler fish can detect with what is effectively their nose that they used to track down and find a female of which they permanently attach themselves so they provide the female with sperm and the female provides the male with sustenance. So if sent is so worthless down there like you're claiming then why can angler fish use it to find mates from potentially over a mile away

[@c0ldNcl34r]

Firefly:*Doesn't live in the ocean* MinuteEarth:"I can't believe you've done this"

[@brandonpiel8789]

It might be that the bar for evolving bioluminescence is lower in the ocean than on land. There are several species of marine bacteria that bioluminesce (such as Vibrio harveyi). For a marine animal to evolve bioluminescence, all it has to do is culture these bacteria somewhere in it's body. Since these bacteria are only found in marine environments, non-marine creatures can't form a symbiosis with them, and therefore, must evolve bioluminescence on their own.

[@brandonpiel8789]

This was originally a response to a post, but I figured it would get more visibility as its own comment.

[@jamesdinius7769]

That only shifts the question. Now the question becomes, why aren't there bioluminescent bacteria on land or in fresh water?

[@brandonpiel8789]

@@jamesdinius7769 that is a very good question. There are lots of organisms that never made the shift to fresh water or land (echinoderms come to mind, but there are many others). It's possible that there's a common thread between these disparate groups keeping them from evolving freshwater and land forms. Or perhaps they just need more time to evolve. Regardless, more research is needed on the subject.

[@missnaomi613]

1) It's okay to not have all the answers. 2) Thank you for a video featuring one of my favorite words/phenomena, bioluminescence.

[@the_undead]

It is okay to not have all the answers but when the answer has been known since like 2001 (whenever the first blue planet was released) if you're trying to make a comprehensive guide you should know. I don't know much about why fireflies bioluminesce because that's not a subject that interests me but practically 100% of oceanic creatures that bioluminesce either spend 100% of their lives or the vast majority of their lives in the deep where there is no natural light, and the reason so much of it is blue is because the ocean attenuates blue light the least so it can carry the farthest, there is one creature I am aware of that uses red bioluminescence because no creature except for that one that deep can see red light at all, and a lot of creatures are bright red because that makes them practically invisible except to this one fish which I forget what it's called cuz it's been quite a while since I last watched Blue planet.

[@j.r.8176]

"It's ok to not have all the answers" What makes you think anyone, let alone a popular channel on the internet, would need YOUR personal approval for whether or not something is ok? What a dumb comment.

[@the_undead]

@@j.r.8176 give you I have with this comment is not the same as yours, some of the answers have literally been known since blue planet's release in 2001. They have an entire 40 minute episode dedicated on creatures of the deep and they provide a reason for at least some of the bioluminescence displayed on the creatures they showcase, not all of them but more than enough for this video to be a little bit more than pure speculation

[@missnaomi613]

@@j.r.8176 wow, nobody needs my approval. But it sounds like someone could use more fiber...

[@eroelser]

Thanks for brightening up my day :)

[@Campfire_Bandit]

Are we able to check for bioluminescence in fossile records? Would it even be possible that humans hunted surface bioluminescent creatures to extinction? If we can do it to megafauna, maybe glowing creatures were useful or cool enough to warrant hunting them over others.

[@wolfhowl2658]

Maybe its because a lot of land creatures are fluffy, or covered in feathers, which would be hard to glow through. And the ones that arent might not often be ones that could benefit from lighting up. Like diurnal reptiles, amphibians that live in shallow water, ambush predators, prey animals that need to hide, or any creature that relys on camoflage in any way to survive. Forest dwelling creatures too, as mentioned in the video. Maybe the fish in lakes dont evolve biolumenessance because lake water is often at least a bit murky, so the glow just wouldn't do much. And even if the water is crystal clear, they aren't always at the bottom, deepest part of the lake. Being glowy when their close to the surface might just get them eaten.

[@cavemann_]

I may be missing something, but could it be because of the relations between the predator and the prey? Normally a predator wants to stay hidden and so does the prey. Perhaps the only species that managed to evolve bioluminescence are the ones that are either at the bottom of the food chain or reproduce really fast? That could explain why no big creatures evolved to produce their own light. Another theory could be that echolocation and better eyesight are just more useful on land simply for the fact that there's a greater amount of obstacles obstructing movement and vision? An animal won't be able to move as freely on land as a fish in the sea in an open space. Anyway this is all really intriguing! edit: ah it seems other comments mentioned something along those lines already :)

[@skybluskyblueify]

Did you list of reasons sea creatures evolved it and land did not [as much] consider the amount of time that an animal is in the dark? Most land animals have a greater percentage of time where they have to deal with either full daylight or at least some daylight. Those deep sea animals spend most times in very dark areas or at least at nighttime levels of darkness.

[@AnubisSolvang]

Just from speculation, land dwelling animals being luminous at night would definitely mean ending up as dinner for predators that have adapted low light eye sight. So that could be explained away pretty easily.

[@umi3017]

Fun fact, at least one species on land have evolved non-bio luminescence, and it started in a way that's almost unable to do under water. Fire.

[@whazzup_teacup]

I think it's a combination of things which makes it hard to determine any specific factor.

[@mr.cauliflower3536]

Kinda this

[@gabrielgrilo1978]

External light may reach the bottom of rivers easier than oceans, since salt water reflects this light easier than sweet water (?). If so, bioluminescence is not very required by larger river animals for vision, but it's a consequence of biochemical reaction to spread (excess of) energy (Ex: microorganisms)

[@massimookissed1023]

Well there _were_ bioluminescent mice, but the bioluminescent owls finished 'em off.

[@eliyahzayin5469]

It might be something like an evolutionary version of a file format. If several species you're competing/surviving with already communicate with bioluminescence, there's going to be pressure to use it as well.

[@jasonreed7522]

It could also be an exponential phenomenon where 1 glowing cyanobacterium 8million years ago diversified and brought the trait into a bunch of other species. (But you still need to explain how every family developed it, because a cyanobacterium ancestor wouldn't have given it to a fish without all fish getting it, nor does it explain the different colors because while blue is most common some predators use red instead)

[@julian_hesse]

I think a part of the puzzle is that on land there is plenty of light during the day. Whereas in the ocean it is always pretty dark unless you are close to the surface. So for land animals it makes more sense to rest during the night and just wait for the light🤔

[@cathygrandstaff1957]

I think it has to do with camouflage. With deep sea fish one theory is that bioluminescence evolved as a way to camouflage themselves against the light coming down from above. With land animals a light source would attract attention rather than deflecting it.

[@coralmaynard4876]

Ok, I just did a bit of research on fresh vs saltwater, and it seems like a big difference is oceans and seas are much more stable in terms of ph and stuff like that, while freshwater is VERY prone to changing on a whim. This not only means that freshwater fish can adapt more easily to change, but also it may have an effect on bioluminescence; after all, if your environment is always changing, do you really want something which may only be useful 5% of the time? Isn't it better to make sure your body can adapt to changes? As for the land animals that produce light, which are all insects btw, it could be a similar case? Ok, sure, maybe a FRESHwater snail is bioluminescence, but it doesn't have to adapt to so many changes the same way freshwater FISH do; of course, it's hard to say for certain... I'll make a guess that if all of them hang around water, bioluminescence makes it easier to see it so they don't drown? Idk, just my thoughts lmao.

[@HeyNonyNonymous]

Bioluminescence works better in an environment where other animals light up too: if it's a common thing you're less conspicuous for predators. And if it's commonly used by your prey to attract mates, it is more effective as a lure, since your prey is already evolved to approach it and has an evolutionary incentive to keep doing so despite the risk.

[@Vistico93]

Now I'm picturing non-avian dinosaurs brightly lighting up at night. Those plates on a stegosaurus lighting up in sequences or the fans of dimetrodons (not dinosaurs, I know) looking all psychedelic like a cuttlefish before it attacks. Pterodactyls with ads...

[@burt591]

75% of animals in the ocean making light sounds way too high, are you sure about that figure?

[@RTOF]

For anyone who missed the first few minutes: the title initially said "The Mystery of Bioluminescence

[@Dyejob01]

Why do you think others missed that?

[@RTOF]

@@Dyejob01 well they changed it

[@SM-mc3ll]

They'll change it again in a day or two

[@sparking023]

Hmm, I may be reading this wrongly but to me it seems the real question is why fireflies developed bioluminescence. In the deep ocean, vast space and lack of food and sun light all lead to bioluminescence being advantageous, but I can't imagine how it would help fireflies in any way It probably has to do with some mating ritual, just like peacocks developed clumsy tails that make them more prone to predation but also more successful in courtship. It could also be some kind of warning sign, just like frogs and vibrant colors, but I don't know if fireflies would be toxic or poisonous to larger animals

[@Grigorii-j7z]

Abandonce of sulphur in atmosphere probably is the main reason for scarce bioluminescence animals on surface.

[@mm-yt8sf]

fireflies seem so innocent to me, they attract attention but as flying things go they seem extremely poor fliers, they don't dart around very quickly..i've caught them with my hand, and they even land on my hand which doesn't seem super wise for a clunky flier 😀i hope they're not easy prey for things that can eat them... also i haven't seen them around as much as i used to...aww.. though maybe i haven't gone outside as much as i used to...

[@dallasjhaws]

has anyone considered differences in predator/prey dynamics? Land prey don’t wanna glow or else they’re an easy target. Land predators don’t wanna glow or they give themselves away. There’s a reason “camouflage” or skin patterns that blend in are so common on land, which is antithetical to bioluminescence

[@davidedevincentis5444]

I think sound and smell might play a role in explaining why bioluminescence hasn't been so prevalent on land. Many land animals are able to navigate dark environments and communicate by smelling and hearing too, even using those rather than sight in many circumstances, compared to sea creatures which are much more relying on sight, since vibrations and chemicals travel much less distance and are less perceivable in water. Maybe evolving a completely new metabolic route to syntetize, break and dispose of a fluorescent substance is much less practical and successful than adapting already existing senses to a new environment

[@legohexman2858]

light goes through air much better than water, especially when that water is filled with life and other particles. also, salt water and fresh water bodies usually differ in geographic aspects such as size

[@wooblydooblygod3857]

I think that in the ocean, due to how large and empty it is, it Matters less to see and more to be seen.

[@darkbeetlebot]

What if there isn't a real reason for the disparity? What if coincidentally, the animals that evolved terrestrially just didn't come from sea life that evolved bioluminescence?

[@brendanrisney2449]

If I remember correctly, all animals are technically bioluminescent- even humans! The many chemical reactions inside of you would produce light if you were transparent.

[@themangix357]

Land animals lighting up under UV, is it also considered bioluminescence? 🤔

[@MinuteEarth]

Good question! Lighting up under UV light is a phenomenon called biofluorescence. An animal is biofluorescent when it absorbs light from a source and re-radiates it in some way. Bioluminescence is when some sort of chemical reaction generates the light we see. Lots of animals are biofluorescent, and many are both biofluorescent and bioluminescent!

[@kirtil5177]

@@MinuteEarth would a chemical process that creates light and is powered by light be both then? as opposed to directly storing and using the sun light, more like turning it into your own light

[@deepfritz225]

navigating a 3 dimensional space as opposed to a (mainly) 2 dimensional space seems like a good candidate explanation.

[@Birginio420]

I think it has to do with the way light propagates in both mediums and the whole spectrum of what can be seen by the organisms.

[@Dyejob01]

Darkness in water, is VERY different, than darkness in the air. Your hypothesis is not correct. For hunting at night, land animals have developed larger eyes, that absorb more light. And can draw more ambient light out of water But animals in the oceans can't draw light the same way, because light is refracted in water. So a strong pulse of light helps draw prey, or repel danger. Please follow up with this hypothesis.

[@thanawitsagulthang6471]

Nice accurate no click bait thumbnail

[@B_Machine]

The deepsea is vast and desolate, and creatures down there are often thought to be few and far in between. Assuming many of the creatures are blind down there, it would be a great advantage if you can retain your vision and use bioluminescence while many of the creatures around you cannot see. The combination of desolation and limited amount of animals able to see you probably makes it more beneficial than not for many to use it. Also, I'd be willing to bet it's more energy efficient to shine a tiny beacon rather than using other methods to signal to mates in a relatively energy scarce environment.

[@francoislacombe9071]

Land animals have extra energy requirements compared to ocean living ones. They may evolve to invest their energy in locomotion, building up their bodies and supporting themselves against gravity, instead of lighting up their environments. That, of course, would not explain why fresh water animals don't use bioluminescence as much as salt water ones.

[@predo70]

Not an expert here, just thinking out loud.. what is biolumenescence in the oceans used for? If it is communication, sound might just be easier to use sound on land (as far as I know very few animals in the oceans use sound as a form of comunication.. and those who do are mamals).. but this doesn't really explain lakes and rivers. Human made light polution is a lot more significant on land as well.. but that is also a recent development, and I doubt it would wipe out all the bioluminescent animals that fast..

[@indigofenix00]

Many bioluminescent marine animals use the same handful of bacteria to light up, and bioluminescent bacteria are free-dwelling in the ocean while they generally aren't on land. Bioluminescence probably starts out with an animal being "infected" with a free-living glowing microbe and gradually getting better at managing, controlling and nurturing their glowing inhabitants. Maybe there's just a lot more opportunity for sea animals to be infected in the first place.

[@jaybingham3711]

If you think about it, the light would work to counteract the effects of darkness. Sure...absurd at first blush. But after some serious and deliberative considerations this really does make sense.

[@holmesferonton7982]

You forgot to mention about glowing mushrooms and fungi that makes bioluminescence too!

[@Kammerliteratur]

and don't forget thst there are a couple of bioluminescent fungi on land

[@TomFromMars]

One thing to consider is the following: when emitting light in a dark environnement, you make yourself detectable from à much further distance than the one you light for yourself. Now if that's a good or bad thing depends on a number of factors and also it's not as true underwater where light doesn't travel as long.

[@arianaink100]

A lot of it comes down to reflection refraction. The sun passes through the ozone layer onto the surface past the water and down to a certain depth. (A star can blast through all of space but only swim down so many meters in our deepest oceans/lakes) There’s more diverse bioluminescence in oceanic life because lakes shift change dry out and reform at a greater rate over millions of years leading to short lived subspecies compared to ocean life that moves with the oceans currents/constantly adapts. (It’s also a scattering method in large groups where your predator has trouble isolating use when in a mass group; as nearly all fish species are schools or work in system it’s rare to find actually isolated aquatic life. (It’s usually just spread out but not isolated as isolation doesn’t offer frequent mating options) ) You’re less likely to get isolated areas that promote growth to substantially lasting species on land due to the rapid changes and tectonic shifts. unless it is a cave lake. (As all the lakes will drain down and out eventually that’s where things persist long term isolated yet thriving. Most organisms can’t survive light for extended periods and some how aspects of luminescence and translucency. (Also unique pockets of minerals which is apparently yummy for micro-organisms and small life forms) and the method of producing luminescence is different in oceanic animals it’s phytoplankton, the consumption of plankton, electro-pulses under the skin or around the body, or reflection of UV light off of surface. On land where there is no phytoplankton there’s more chlorophyll things are different. Things with high sugar contents or necessities aren’t going to be UV reflective they want to absorb UV. (Attracted to UV - bees/moths/butterflies (pollinators of plants that absorb light and a difference between solar light vs moon light reflections/amount of light) So that leaves a few species on land or water that in the morning glow. (You’ll notice desert animals like scorpions and other arachnids do glow in UV light, they rely on temperatures, exoskeletons to be durable in the environment and reflect light away.) (fireflies has a chemical changed that’s created but the bug still eats and processes sugar/proteins. It’s just an adaptation and it’s the last of its species on the brink of extinction so it’s not going to be an option many other insects take, we might se a subspecies of a totally different bug mutate to fill that role or we may not it may take millions of years. The best bioluminescence on earth is found in fungi with the greatest range of biodiversity. You’ll notice it’s also a mostly noticeable nighttime activity/dark dank location/semi wet environments. They network and utilize water and wet areas effectively enough at reproducing rates to have varied methods and visual glows and like many other smaller species scatter effectively in semi warm warm water and dark locations. Fungi are the equivalent of the En-mass glow method even if they utilize different food sources due to location/atmosphere/habitat differences. Gravity is a bit different in the ocean I’m sure a fungi would dream of swimming if they didn’t choose to completely dominate the earth as one of the first living things on land, utilizing air dispersal along with water instead of just floating water they both use gravity but it is different ways of moving.

[@xoxb2]

Is it not because light is detectable in water to a far greater extent than are sound and smell? As someone else has pointed out, light emitting body parts are usually fragile membranes that we can't risk on the outside of our bodies if we live on land. Still, the freshwater mystery remains ...

[@melskunk]

Now I'm really wondering why there isn't ANY bioluminescence in lake Bikal. It even has seals!

[@gigabyte2248]

Well, the zoomed-out systems answer is that the benefits outweigh the costs (and vice versa). The video went over the main benefits in brief but it barely discussed the costs at all (and IDK if science yet knows the evolutionary costs of bioluminescence). The costs probably hold a clue here. We've seen that there are a handful of minor evolutionary pressures encouraging sea animals to bioluminesce where land animals don't, and if the cost is moderate then it would make sense that sea animals find it worth the cost to (evolutionarily) push through the difficulties, whereas it's not worth it on land.

[@ginnyjollykidd]

Lightning bugs get together in, say, a tree, and all light up in a beautiful, coordinated fashion, something like Christmas lights. This, like cicadas, helps them find mates _en masse_, making lighting up an efficient way of continuing the species. ("If you can't be with the one you love, love the one you're with." Wisdom from Fleetwood Mac.)

[@OxalisTuberosa]

i _cannot_ be the only person who saw the thumbnail, saw the title, and proceeded to read the title to the tune of fireflies

[@WilliamBurton8]

Could it be that surface creatures who evolve some form of very low level light just isn't seen and, therefore selected for, whereas deep sea creatures are in such pitch dark conditions that even a small adaptation is seen and selected for, therefore allowing it to flourish

[@Slayer_Jesse]

0:47 I see you, sneaking in a Pokemon there.

[@kennarajora6532]

KZbin needs to stop these double ads.

[@CCRUEnthusist]

Guess no one asked for: size of ocean + lack of sound as means of communication. Being a truly 3d environment it might be much easier to miss mates. And with no way of communicating at a distance it would make sense to use light as that method.

[@Corruptedhope]

Nothing has to be rare to be unique

[@Mitobu1]

when they say 75% of animals, I assume they mean number of species, and not number of organisms I have a few ideas on this. 1. animals that light up underwater are easier to find, and thus identify. I am sure we havent sampled the full biodiversity of the ocean, so saying that 75% of them have bioluminescence is likely because we havent found the creatures that dont have it. essentially, discovering the creatures with bioluminescence at a much greater pace than those without. 2. If this isnt an example of observation bias, another means is that these bioluminescent species are likely algae, plankton, and other microscopic creatures. this inherently balloons the number of species because of how we categorize different microorganisms 3. in water, these bioluminescent organisms can cluster together in three dimensions rather than on a planar surface as terrestrial creatures are forced to do. Because of this clustering, intensity of light scales with volume, rather than area, which means the benefits of producing light will apply selective pressure faster than the terrestrial case; resulting in bioluminescence being a more accessible and reinforceable adaptation in aquatic species.

[@adrian_be]

Maybe it's because more infrared is used outside of the water. Nocturnal animals use infrared (or ultrasound in bats) to find prey. Underwater theese methods might not be as effective, which is why bioluminescence is more common there

[@inlean3224]

THERE ARE GLOWING MILIPEDES?!?! Lord have mercy, that looks so cool

[@himedo1512]

I'll come up to bat and think i have a decent Theory. Surface land creatures do not because, bioluminesce offen goes with being transulucent to be more efficient. Which makes one vulnerable to UV rays and sunburns. Ovbiously all surface dwellers will have to deal with day time eventually. only a few feet of water stops 20-60% of incoming UV rays and the deeper you go the less it affects, so its less impactful to ocean life. Further most of the ocean is empty and massive. The earth's surface has topography, so its not actually helpful for being seen. Also, the earth's nights are dim not dark. The light from the creatures has to compete with the stars and moon. And the surface is more population dense, the ocean is very sparsely populated with visible creatures. So actually being able to be seen is important for finding mates, while the high density on the surface means you can easily already find mates but the light alerts predators. Basically its not on land, because its less efficient, effective, and makes them more vulnerable to UV and predators. Its not common in caves because caves are not vast like the ocean and the caves are not typically very open. Thus, the same density problem and effectiveness problem. Its not as effective due to terrain and caves are small enough you can find a mate without it and the light would attract predators. And now its redundant because most cave dwellers also can't see. Freshwater bodies are a little harder to explain but i believe its still the density thing. A lake is still far more dense than the ocean thus easier to find mates without it and easier to get eaten by predators with it. To me a large factor definitely seems like population density

[@audio_boys]

Have we really ruled out depth? Creatures that go deep enough, like really deep, seem to develop it more, and those creatures could always then readapt to swim shallower. It's possible that this is the cycle that keeps creating it and that lake just isn't deep enough or varied enough to begin that cycle.

[@AvangionQ]

My guess is that we'll find the answer only after examining the genomes of all bioluminescent species for similarities in their gene pools.

[@lostbutfreesoul]

If I had to hazard a guess I would say... it is complicated, no single one cause. If I had to point to a primary one - what about the thickness of water compared to air?

[@Michael-sb8jf]

Imagine a glowing orb weaving spider

[@Noeabe]

0:45 The Chinchou in the corner :D

[@saliso470]

Snakes bats and owls probably wouldn't like glowing while trying to hunt something

[@Dhorannis]

Not really, but imagine a spider luring moths into its net with light.

[@YeszCore]

Selective pressure for it may just be higher in the ocean? If a competitor acquires this adaptation, there’s really no substitute for it. Could it also be related to the microorganisms that often cause bioluminescence?

[@nirvanachile24]

"We don't know why animals might need light, but it might be because of darkness."

[@noahschwarz318]

How about we(mostly) only find the ones that shed light deep down?

[@pherrisfallus7259]

Wouldn't the insulation and protection common on land animals like fur, feathers, and scales block out the light produced? Also shadows are easier so glory secretions would be less effective if they are under a leaf or something. Not to mention the having daylight sometimes also makes bioluminesence only effective less than half the time

[@neomt2]

Arthropods no longer have gills, they evolved lungs before vertebrtes

[@NelsonDiscovery]

It's not a paradox.

[@D1vu5]

Personally, I think it is just that smell is a better alternative on land, possibly easier too.

[@jamesdinius7769]

Smell works just fine in the water. You know, sharks smelling blood and all?

[@Kaikaku]

You forgot another land species with about 8 billion individuals, that also developed bioluminescence ;)

[@Dmittry]

You are talking about visible to human eyes light. But what about other spectrum? Maybe there are more land species that emit electromagnetic waves invisible for us (beside infrared light caused by temperature of course).

[@cynthiarowley719]

What is the advantage of making light? Even lightning bugs only flash their lights when the sun goes down. Emitting light for something to see, just not humans.

[@notsocube8452]

0:52 There's a pokemon on the left. Idk if it's a real animal but that's definitely a pokemon on the left Edit: There's another pikachu here on this vid

[@Alienfish20]

So if you've ever seen a picture of your retina, you would instantly understand where bioluminescence is prioritized in land dwelling animals

[@americanmapper2445]

🎵You would not believe your eyes🎵

[@Don_Melon]

i also light one up when I'm in the ocean

[@TheLazyComet]

wonder if it has to do with the fact that some animals glow under UV light. no need to make your own if you glow by the sun

[@Alphoric]

What I find cool is how carbon offsetting doesn’t do anything at all 😅

[@hollow_ego]

At 0:51 there is a Chinchou

[@TrevorJrHotkiss11]

It's because the entire environment is dark. Caves and nighttime environments vary, specifically the organisms going in and out. The ocean is more of a closed environment with consistent darkness among organisms vastly distant from one another. Organisms in caves would adapt to other organisms or factors that come from outside their caves. Those factors don't depend on darkness. A bug that requires light wanders into a cave and gets eaten by a bat it can't see. If the bat was bioluminescent, it would be detected by the organism adapted to light perception. Ocean creature that's evolved in darkness wanders into dark area of water and is able to detect hidden predator and avoid being eaten. The evolutionary pressure for needing light is significantly more important in the ocean depths than a cave. There are already light sources available, and caves are simply unique unclosed (as in the surface organisms and cave organisms are not mutually exclusive) ecosystems. A bug doesn't constantly exist in darkness, just when it enters caves or its night. So it's not nearly as important and not a significant enough evolutionary pressure. An ocean dweller would need lights to see.

[@TrevorJrHotkiss11]

The selection pressure for bioluminescence is significant in the ocean compared to the land, even caves and the night. It seems very simple to me. They require light to see waaaaay more than the other environments. Caves being dark is good because it's a great trap for light adapted organisms. Same as night. If predators or even prey became bioluminescent, there would be a different dynamic with nocturnal predators. There isn't an equivalent lighting contrast in the ocean to a day-night change on land or walking into a dark cave during a bright day. Those environments have different selection pressures. Too long didn't read; Selection pressure, environment, lighting, predator and prey.

[@nataliejanewallace8376]

Thank you

[@KSeigY]

I'd imagine that the frequency of bioluminescence in the ocean is has similar circumstances to having flashy colors (possibly even like some organisms in coral reefs do). Warnings to predators (stay away, am jellyfish. Or I want you to think I am). Social benefits, with far lower visibility distance in water that you'd have thru air, meaning you might be able to communicate with others of your species without, being spotted at a distance (or not as easily, anyhow). Perhaps it might double as comoflauge like zebra stripes do (with the primary being social or other "more direct" uses) if the bioluminescent creatures commonly congregate together. As for lakes, it could just be that none of those benefits were ever as strong as they might be in the ocean, or the downsides might be much more of a disadvantage there than in oceans. This is all just speculation on my part, it could be wrong just as easily as it could be right (most likely to be mostly incorrect, or small part of the reality if true at all)

[@crli4353]

I would say a possible explanation for the is LIFE itself. This planet is one big ball of life consisting of countless eco systems. What we find over and over (particularly where humans haven't interfered) is a harmonious balance in life. Certain animals develop characteristics that allow them to sustain their existence in their eco system. This is why we dont see a natural over or underpopulation of any one species, besides humans of course. I would say the reason why we dont find bioluminescence in certain places, like deep fresh water lakes, is because there is simply no need. All the animals in that eco system live in balance and thus there is no evolutionary purpose for the addition of a new trait. Occam's razor

[@TheyCalledMeT]

Hmm i would say there's a dimm uv radiation which allows sight outside of water which makes the unique benefits of bioluminescence superfluous and since it comes with a cost.. it doesn't benefit but handicap animals on land

[@mxte42069]

0:53 aye bro das a pokemon on the left top right corner

[@liamaviv6574]

I think it’s because of different predators in land rather than water

[@Elseheli]

I love this kind of videos that make me asking about the nature and the existence 👌👍

[@DigGil3]

The deep ocean is lit.

[@Guilgd]

a tottaly unexpert guess, but what about heat dispersion?

[@Kurrian333]

I see that Chinchou cameo

[@erictaylor5462]

But even at night with no moon there is still quite a bit of light on land. Not enough for humans to see. After all, humans are diurnal. But with some training you can still see enough even when your only light source is starlight. If you are a nocturnal animal you can see quite well in the dark. The horseshoe crab has eyes that can become 1000 times more sensitive to light at night. As there is about 1000 times more light in the day compared to the night, this means that the horseshoe crab can see as well at night as it does in the day. As to why there are no bioluminescent creatures in fresh water lakes. Fresh water lakes are very short lived compared to the seas. The seas have existed for billions of years, pretty much as long as the Earth has existed. Ocean floor is constantly being recycled and remade so sediments have a limited time to build up. In lakes this does not happen so fairly soon, perhaps after just a few million years lakes tend to fill in.

[@ciaragarrity6425]

You know there several land animals that are luminescent, have you seen CuriosityStream's show?

[@tearren1]

When i was little I used to like to hold a flashlight up to my flattened hand in the dark bc I thought it was cool.

[@azarathe5901]

could it be because the ocean already has bioluminescent life and as such it wouldn't gather much attention from predators?

[@lolglolblol]

Aliens. It's always aliens.

[@ezapi]

That Pokemon in the water creatures though