NOVA

NARRATOR

They're some of the most dynamic, dazzling, jaw-dropping displays in nature.

EDIE WIDDER

It's these rocket ships and explosions of sparks and spewing of what looks like blue smoke. And these long chains that look like Japanese lanterns extending off into the distance as far as you can see. It's magic!

NARRATOR

Some flash. Some sparkle. Others simply glow. But most we're only beginning to discover. Suddenly we recognize it, and now we find it everywhere under there. Hidden in the deepest, darkest, most remote stretches of our planet, these luminous critters can be timid performers. But the closer we look, the more we realize the light they create is pervasive.

JOHN SPARKS

If it wasn't important to the organisms, you wouldn't see it all over the tree of life.

NARRATOR

Now scientists are thrusting these cryptic creatures and their fantastical displays into the limelight. Some are even attempting to harness this light, co-opting millions of years of evolution for the betterment of our own dim species.

DAVID GRUBER

We have to go down to the ocean to find these animals that give off light so we can then understand ourselves. To me, it's a beautiful connection.

NARRATOR

We're shedding light on the "Creatures of Light," right now on this NOVA/ National Geographic special. It's one of life's essential ingredients. We soak up its energy. Set our clocks by it. Need it to see. Light is so precious to us humans, we've coaxed it into lasting all night long. But imagine a world without it. (blows) While we're cursing the darkness, countless thousands of other species have evolved a much brighter response without burning an ounce of fossil fuel. It's called "bioluminescence." Living light. And from glowworms and fireflies to plankton and jellyfish, it's been lighting up the dark for hundreds of millions of years.

JOHN SPARKS

If you look across the tree of life, essentially, bioluminescence is splattered all over it.

EDIE WIDDER

It's just everywhere you look. How to survive in the dark? Make light.

NARRATOR

On land, where it's dark only at night, just a fraction of creatures evolved the gift of glow. But descend into the deepest depths of the oceans where the bulk of earth's creatures reside, and you find a very different story. Down here, as many as 90% of life-forms shine.

MAN

I'm going to come off the wall and head out into open water. Surface, surface, this is Nadir. Our present depth is approaching 100 meters. Life support okay.

NARRATOR

That's why a team of scientists from New York's American Museum of Natural History is here, plying the dark waters of the South Pacific Ocean in search of new luminescing creatures.

MAN

I'm going to start motoring away here.

NARRATOR

They've journeyed to the other side of the world to the pristine and remote waters of the Solomon Islands to unravel how and why light-producing animals evolved, and perhaps put their living light to work for us. David Gruber is a marine biologist.

GRUBER

After about 100 meters in the ocean, you get into this twilight zone. About one percent of the light makes it down. So as we start getting deeper, you'll start seeing almost everybody down here. Every fish that we see has this ability to blink or flash or communicate, producing its own light.

NARRATOR

The problem is, common as bioluminescence may be down here, it's challenging to study, even with a submersible. The water is too dark, the distances are too great, and the light the animals give off is too unpredictable. It's a tough environment for marine biologists to work in. But a neuroscientist like Vincent Pieribone feels especially out of his depth.

PIERIBONE

I'm a scientist that spends most of his time in a laboratory. So it's very scary, to be completely honest with you. You've got to keep your head and your wits about you and try to focus on what the job is and not really think about the fact that there's, you know, a few tons of water on top of us at the moment. But we're here in the name of science, so we press on. (laughs) Ooh! That's a photophore.

NARRATOR

One goal for this trip is to develop a better low-light camera. Deep-sea bioluminescence has only been filmed in the wild a handful of times. Most of what we know comes from observing animals in carefully lit tanks on the surface. (splashing) Whether it's the infamous anglerfish with its luminous lure or the light-packed viperfish, one of the deep's most ferocious predators, scientists typically collect them in small trawl nets like these. Bob, you're gonna turn around the net, right? Yeah! All right, thanks. They then examine their unique light-producing organs to infer how they work. That's what biologist John Sparks is trying to do with this viperfish. They may be fierce, but even the big ones are actually pretty small.

SPARKS

This is a monster for these things. There are a bunch of different species. They're hard to tell apart. I've actually never seen one that big. We still know so little. That's what's kind of frustrating. You've got to get the organisms up alive, which is tough. You've got to be able to image enough different species to make it meaningful. But in terms of us doing anything scientific with it, it's very tough because we've got so little data.

NARRATOR

What scientists want to understand is how luminescent features became so pervasive in the deep ocean. And why, in a world full of predators, would animals invest so much energy into lighting up and standing out in the first place? They are questions marine biologist Edie Widder has been grappling with for decades. An expert on living light, she was among the first to study it underwater.

EDIE WIDDER

I wish I could describe what it's like to be down there, because I would like people to be able to appreciate it the way I have. It's these rocket ships and explosions of sparks, and spewing of what looks like blue smoke, and these long chains of siphonophores that are like chains of jellyfish that look like Japanese lanterns extending off into the distance as far as you can see. It's magic.

NARRATOR

Edie devised her own methods to trigger these underwater light shows. She mounted a large screen on the front of her submersible. When creatures bump into it, they light up, and her low-light cameras record them in the act. Over the years, the aptly named Splat Cam has helped bring to light some of the most bizarre creatures in the deep. Everything from jellyfish to sea cucumbers.

WIDDER

The open ocean is the biggest living space on our planet by far, and it's a very unusual environment. There's no trees or bushes to hide behind. But animals have to play all the same games of hide-and-seek that animals do on land. And that's where bioluminescence comes in.

NARRATOR

In this deep, dark abyss, light, it seems, is vital, and creatures have evolved to wield it in many different ways for many different reasons. Tiny organisms called dinoflagellates, for example, alight in unison whenever the water around them is disturbed, taking the shape of whatever swims through them. It's a treat for the lucky few who get to bask in their soft glow. But for predators of these microbes, like shrimp, it's more like tripping a motion sensor. Every time they make a move, the lights come on and give away their location. Predator becomes prey to a host of other creatures, like cuttlefish. But some shrimp are armed with their own light-filled defenses. When threatened, certain species shoot bright flashes of light to stun and confuse their enemies.

WIDDER

There's a lot of animals that actually can release their luminescence that way. So you can have something like a shrimp that will spew luminescence out of its mouth like a fire-breathing dragon and temporarily blind its predator while it pulses away into the darkness.

NARRATOR

Rather than blinding their predators, a huge variety of fish, from squid to sharks, use light to hide from them. It's called counter-illumination, and it may seem counterintuitive, but consider how a fish swimming near the surface appears to a predator in the depths below. As sunlight or moonlight beams down on them, their silhouettes are plain as day.

WIDDER

And so an enormous amount of animals in the ocean produce bioluminescence from their bellies that exactly matches the intensity and the color of the sunlight coming down through sea water.

NARRATOR

When the lights come on, the animals vanish.

WIDDER

It's an amazing cloaking device. They just disappear, utterly disappear.

NARRATOR

Others, like ostracods, tiny shrimplike critters, use light a bit more extravagantly. They ooze light to stand out and impress the opposite sex.

WIDDER

Ostracods, which are about the size of sesame seeds, produce a crazy amount of light for such a little organism. And they'll squirt out one little dot, and then they swim a little further and they squirt out another dot, and another dot. And the spacing of the dots is species-specific, and so the female can recognize the male that she can mate with. So it's almost like skywriting, but it's light writing. It's beautiful.

NARRATOR

But mates aren't the only creatures light attracts. Many fish use light to lure food in, as does the most notorious bioluminescent creature of all. What is that? It's so pretty.

WIDDER

Remember that ugly angler in Finding Nemo? Good feeling's gone. (screeching) That lure is actually meant to attract another fish or another little shrimp that comes to gobble it up... (screaming)...and then finds itself engulfed in this living mousetrap of needle-sharp teeth.

NARRATOR

Lures. Motion sensors. Cloaking devices. All together, bioluminescence lights up the deep like an aquatic Times Square.

GRUBER

Bioluminescence was a tool that was laying out there, and somebody was like, "I could use it for this," and somebody's like, "Well, I could use it for that."

SPARKS

They use it to find food. They use it to avoid being eaten. They use it for mating. And they use it to communicate with each other, just like all these signals are trying to communicate with us. Things that are very important to not only the individual but the species as well.

NARRATOR

Despite all the risks, light is a shining example of Darwin's theory of evolution. From bacteria to jellies to fish, it helps organisms survive.

But the question remains

how did the initial spark for this light arise? To find out, scientists have turned to a different set of bioluminescent creatures, ones that are a bit more familiar and easier to study. Land critters have evolved their own special ways of using light. Take the glowworm, for example. Like anglerfish of the deep, thousands of these fly larvae light up the roofs of these caves in New Zealand like the night sky to lure in a meal. The starry ceiling fools prey like flies and moths, which are attracted to the light. As they fly upwards, they get trapped by the glowworms' sticky, threadlike snares. Rather than luring prey in, other bioluminescent creatures, like this millipede in the Sierra Nevadas, uses light as high-voltage signs to keep predators out. The bugs are laced with cyanide. Their nuclear glow alerts potential predators to leave them alone. And then there are probably the most familiar displays of all. The brilliant flashes of fireflies are some of the most sophisticated mating strategies ever evolved, the ultimate in romance languages. By triggering a chemical reaction in their abdomens, male fireflies can turn themselves on or off on cue. And if they do it just right, they'll turn on female fireflies too. University of Florida biologist Marc Branham has devoted the last 15 years to deciphering this elaborate language of love.

BRANHAM

It's like breaking the code.

NARRATOR

A secret code that has two parts.

BRANHAM

If you actually measure these flash patterns very, very carefully, there are some features that are always standardized, and we think those are the parts of the signal which say, "I'm a member of the following species."

NARRATOR

One of the 2,000 different species of firefly, which are actually not flies at all-- they're beetles.

BRANHAM

There's also parts of the signal that have a lot of variation across individuals.

NARRATOR

This second set of flashes is personalized. The timing differs from fly to fly within a given species.

BRANHAM

Males are telling females, "I'm a member of this species, but also, here's a little bit about me." It's the females who actually make the choice. They can see all these males flying around flashing, and they see lots of variation in those signals, and some are more sexy than others, and so those males get a flash response by the female.

NARRATOR

Thanks to their enormous eyes, shaped over the eons to detect faint light, the males see the response and home in on the female's location.

BRANHAM

He'll flash back to her, she'll flash back to him, and they'll have a short dialogue until the male finds out where she is exactly, and he will land right beside her. It's Valentine's Day.

NARRATOR

It's the equivalent of strutting tail feathers, or chirping and croaking. To succeed in the reproduction game, you've got to make yourself known, and light is an effective way to cut through the chatter.

BRANHAM

I mean, how can you miss a flash on a hot summer night?

NARRATOR

So how do fireflies, and everything else that lights up both on land and at sea, produce these brilliant flashes? It turns out the luminescing beetles were the torchbearers for finding that out. In 1885, a French biologist working on a firefly cousin called Pyrophorus deciphered the chemistry responsible for their magical glow. He determined it's the result of a reaction between two chemicals, which he named for the fallen angel Lucifer, the light bearer. One chemical, luciferin, acts as the fuel, kind of like gasoline. The second, luciferase, is an enzyme, which fires the reaction like a spark plug. When the chemicals are mixed together in the presence of oxygen and some other key ingredients, they react, and the excess energy is given off as light. Over the last century, this light-producing reaction has been discovered scattered across the entire natural world, both above the surface and beneath the waves. That's how readily available these ingredients are. The actual chemicals differ from creature to creature, but the basic mechanism of fuel and spark is the same from flies and worms to jellies and fish, to snails, even mushrooms. The reaction is so common, it has evolved independently on different branches of the evolutionary tree more than 40 separate times.

SPARKS

You find it from single-celled bacteria up through things like starfish, jellyfish, up through the vertebrates, fishes. It's evolved so many times in so many different lineages. I mean, if it wasn't important to the organisms, you wouldn't see it all over the tree of life.

NARRATOR

When it comes to the survival of a species, nothing holds a candle to light. But living light turns out to come in a variety of flavors, and back on their ship in the Solomon Islands, the scientists from the American Museum of Natural History are now preparing to study an altogether different type. Unlike the bioluminescence of the deep, this second kind found in shallower waters doesn't produce light of its own. Rather, it absorbs light from an outside source, soaks in its energy, and spits it back as a different color. It's called biofluorescence. (dance music playing) And anyone who's ever danced under a black light or watched fingerprints light up on a crime show is familiar with the concept. Fluorescent chemicals absorb light in a unique way. Down at the atomic level, light jolts electrons into more energetic orbits around the nucleus. When they fall back to their original state a few billionths of a second later, the electrons re-emit, or fluoresce, the light back at a lower energy level, giving off a different color. Fluorescent animals work the same way, only their special chemicals, typically fluorescent proteins, are built into their skin and other tissues.

PIERIBONE

Biofluorescence is an odd property because the animals don't actually produce any light. You shine one color light and they'll produce a second color of light. And it's a pretty rare phenomenon.

NARRATOR

That's because unlike bioluminescence, biofluorescence requires a special set of conditions to occur in nature. It needs sunlight to make light, but not sunlight as we know it up on the surface. When it hits earth, sunlight contains all the colors of the rainbow, as light going through a prism reveals. Eacholor is the result of a different wavelength of energy. But once the light hits water, things get interesting. Water acts like a filter, and the different wavelengths are only able to penetrate to certain depths. Long wavelengths, like reds and oranges, fade out first, then yellows and greens, and then finally, a sea of blue. And this pure blue light turns out to be the perfect trigger for fluorescence.

PIERIBONE

So they take the blue light that's coming to them in the ocean and they convert it to greens and reds, and that gives them this color, this contrast.

NARRATOR

Depending on their chemical composition, different fluorescent proteins give off different colors, all of which can be hard to see. Without special filters, visible light can wash it out. That may explain why it's gone unnoticed for so long. How animals use fluorescence is still a mystery. In corals, where fluorescence seems to be the most prevalent, it may be used as a kind of protective sunscreen, deflecting harmful UV light or absorbing dangerous byproducts of photosynthesis.

PIERIBONE

So the coral is this piece of rock with a skin coat of a few cell layers on top, and in that layer, it's packed with this fluorescent protein. These animals are doing a lot of work to produce a lot of this protein.

That's the mystery

why are they doing it?

NARRATOR

For years, fluorescence was thought to be confined mainly to corals and some jellyfish. But recent finds reveal it may be much more widespread. And in 2012, while shooting a mosaic of fluorescing corals off the Cayman Islands, David Gruber and John Sparks had a big "Eureka!" moment.

It's like 10

00 at night, we're diving on the coral wall, we're about 80 feet down. We're photographing lots of little montages of a coral reef and we stitch it together, and when we got back to our lab at night and we're looking through our photographs, and there it is, like, this bright green fluorescent eel in one of our photographs.

NARRATOR

It was the first time they'd ever seen a fluorescent fish in the wild.

SPARKS

We said, "What the heck is that?" and we thought it was a joke, that the guy, the photographer who was with us had Photoshopped something and was just playing with us. I'm turning this light up?

GRUBER

We didn't believe it at the time. We just checked our lenses. We thought there was some kind of glitch in the camera. Essentially, we got photobombed by a reclusive green fluorescent eel. Can we get in on these guys down here?

NARRATOR

The eel opened up a whole new world for the scientists. It just keeps turning it on. Armed with blue lights and yellow filters, the team started seeking out fluorescence closer to home, in aquariums. Hey, this guy right here. They found it everywhere, all the way up the food chain. Man, check that out. In seahorses... Rays......and even some sharks.

MAN

They're going pretty good! Did you get it? I saw the shark glowing like crazy.

NARRATOR

All have been hiding their true colors in plain sight.

MAN

Whoa, there it is, the fluorescent one. Look at it, you can see it from here.

SPARKS

We're kind of looking back and going, "Why didn't anybody see this?" and you know, you probably just think it's a bright fish, right? You don't know it's fluorescing until you start looking. Once you start looking, then it's all over the place.

NARRATOR

To find out how prevalent fluorescence is, the scientists needed to move beyond aquariums and study it in the wild.

DIVER

There's a lot of nice ledges kind of cut into the reefs.

SPARKS

These little guys are gobies, or blennies. What's nice about these guys is almost all these little groups are fluorescent, really fluorescent. These fish here look exactly alike, but they're all different species. And if you put them under fluorescent light, they look really distinct.

NARRATOR

In the monotonous, blue underwater world, the fluorescent splotches and stripes may act as secret barcodes, signaling fishes' identity to potential mates. It's an idea made even more compelling when scientists look closely at the fishes' eyes. Unlike human eyes, many fluorescent fish seem to have built-in yellow filters. The filters block out the ambient blue in the water, letting the vibrant colors of fluorescence stand out. This world that's been hidden to us may be plain as day to the fish.

GRUBER

The coral reef is one of the most competitive environments in the world. It's one of the most biodiverse. Everybody's fighting for space, so by having this ability to fluoresce, they're creating a richer world for them. And now for the first time, we're beginning to see this world that they've been seeing for millions of years.

PIERIBONE

Yeah, let's test it. (faking

German accent)

Bring in ze patient!

NARRATOR

For neuroscientist Vincent Pieribone, the discovery of new fluorescent animals is particularly exciting. Impressive. Wow, it's brilliant, brilliant. He's especially interested in the proteins that make the fish fluoresce. He's hoping to use them to light up living nerve cells and ultimately map the human brain.

PIERIBONE

The inside of the brain is a black box. It's probably the most amazing instrument on the entire earth. Nothing else comes close to the ability of the human brain. And yet we don't have even a very thin understanding of how it works. So we have been in the ocean looking for proteins that we can put into nerve cells so that those nerve cells glow. And we interpret that information and find out how the brain is doing what it does.

NARRATOR

Scientists use fluorescent protein to light up the inner workings of cells. The initial work began with a green fluorescent protein, or GFP, which was initially isolated from this jellyfish.

GRUBER

Green fluorescent protein is like a little bicycle reflector that you could tag onto any protein, and then you'll watch in real time that protein moving about the cell in a living cell.

NARRATOR

To do it, scientists take the gene that carries the recipe to make green fluorescent protein and insert it into cells. Once the genetic instructions are inside, the cells make the protein. When scientists hit the organisms with blue light, the targeted cells fluoresce green.

GRUBER

So this revolutionized our ability to see at the protein level inside living cells.

NARRATOR

GFP was a Nobel Prize-winning discovery, bringing to light everything from the way cancer spreads-- these are malignant cells traveling through blood vessels-- to how viruses infect and replicate. Here is HIV, the AIDS virus, spreading from one cell to another. If scientists attach GFP to virus-resistant genes and insert them into the DNA of animals like mice and cats, they can even assess potential cures for AIDS, lighting up entire creatures in the process.

PIERIBONE

So GFP was a beautiful discovery. It allowed people to see cells in green. So it makes essentially what's completely invisible, visible.

NARRATOR

Scientists have since manipulated GFP to fluoresce different colors......enabling them to tag different cells at once.

MAN

Very green. Yeah, it's beautiful.

NARRATOR

They've also gone beyond that, mining the deep for new fluorescent proteins and finding colors across the light spectrum. But human brain tissue presents a unique challenge. It's quite dense, and none of the colors discovered so far could easily pass through it. So neuroscientists like Vincent have been looking for colors with longer wavelengths, like far reds and infrareds, that can.

PIERIBONE

Reds are a little bit better, they go a little bit deeper, but infrared will pass all the way through the tissue. So for neuroscientists, the holy grail has always been as far red as possible. Yeah, exactly. Got it! So getting these things out of the ocean is really key. It's the only place they've ever been found, and we're back here again looking for ones with different colors, different intensities. So that's our mission.

NARRATOR

To find the glowing creatures Vincent needs, the team dives at night, when there is no natural light to obscure their vision.

GRUBER

We are getting ready for a scoping mission. We'll be looking for biofluorescence out here on the reef, and we're going to be using this camera.

NARRATOR

To stimulate fluorescence, they'll shine blue lights that match the blue found underwater during the day and look through yellow filters, just like the ones the fish see through, to block out the blue light they're shining.

GRUBER

So this way, we can be sure that everything we see in here, the different critters that we're looking at, are truly biofluorescent. Ready to roll? Yep.

NARRATOR

The divers have to get pretty deep, about 100 feet down, approaching that special zone that during the day is awash in blue, the most likely spot to find fluorescent animals. The reef is dramatic, even under blue light. But when the team looks through their filters, a different world comes into view. A technicolor dreamscape. Vincent and David scan the reef for novel sources of fluorescence.

PIERIBONE

We look around in the reef, we swim around,

and we identify something

everything looks black except those animals that are sending light back at us, and there's coral and there's crinoids and there's anemones and there's fish all giving this back. And I can take a tiny bit of a single animal, or a tiny part of an animal, and you can sequence its entire genome. Now you have everything you need to know about the animal genetically.

NARRATOR

They're especially interested in glowing red animals, and there's no shortage of them down here. But not all red animals are useful. Some depend on multiple proteins to produce the color, making them too complicated to study the brain. To hedge their bets, they grab as many interesting samples as they can.

MAN

Top of the evening to you. Hey, mate, you wanna kill the engine for me? You're enough off the wall. You had some friends out there, huh? Yeah, it was really sharky out there tonight. (all talking excitedly) This one, this thing right here, the leafy thing right here, unbelievable, you see it? Like a Christmas tree. And I got another one of these guys and I got a tunicate. Let's get them back and look at them. Yeah, that was unbelievable.

NARRATOR

Back at the ship's lab, the scientists anxiously examine their catch, once again simulating the ocean blue with their special lights and peering through their yellow filters.

MAN

And this is what? This is the soft coral, right? Yeah, they are. All right, so let's go through here. Oh, my goodness, it's very nice.

NARRATOR

Anything promising gets a closer look under the microscope. What is it? That's crazy, you think it's a coral? No, and it's only on small parts. I wish this boat wasn't shaking so much. (laughs): Somebody radio up.

MAN

Somebody radio up to stop moving the boat.

NARRATOR

Not everything they collect turns out to be fluorescent.

MAN

Nothing. It's not fluorescent at all. No. Not a single bit.

NARRATOR

They do isolate several interesting green specimens, photographing and freezing away each one. And then, finally... There you go! Red.

PIERIBONE

Ah, that's beautiful. That's the red fluorescent protein we're hunting for. We're shining blue light on it, but what you're getting is red light coming out. So that's the whole... that's the trick to fluorescence. Check that out. Looks like fire.

NARRATOR

The scientists won't know if they can isolate the red fluorescent proteins until they get back to their labs onshore. Even if they can, it's still a long shot whether they can turn them into useful probes to study the brain. I'm getting pumped up now. Look at that. Good stuff. Isn't that awesome? But for now, this is as close to success as they allow themselves to hope for.

PIERIBONE

Science must march forward!

NARRATOR

Back in New York, John Sparks and David Gruber rescue their samples from the deep freeze at the American Museum of Natural History and begin the painstaking process of carefully examining each of their hundreds of fluorescent specimens. From one eel just a few years ago, the scientists have now discovered fluorescence in more than 200 species of fish.

SPARKS

Biofluorescence is found all over the tree of life, but just like you see for bioluminescence, it's like somebody just took it and threw it at the tree and it kind of stuck in certain places, no clear pattern to it.

NARRATOR

Now it's a matter of extracting the proteins from the diverse creatures, starting with a bit of tissue.

GRUBER

We only want to isolate the little bit of the tissue that is fluorescent and nothing else. Let's go from over here. Extraneous tissue, yeah. Here to here. Yeah. Perfect. Now let's go into here. Beautiful.

NARRATOR

From this, they isolate the genes that make the proteins causing the critters to fluoresce, and then send any promising targets off to Vincent.

PIERIBONE

This is exactly how a plate should look, nice and distributed. They should be far enough apart.

NARRATOR

At Yale, Vincent and his colleagues try to turn them into tools to understand the brain. Using genetic engineering, they fuse the fluorescent proteins to others that are sensitive to voltage, the language of brain cells.

PIERIBONE

So that'll run for an hour. Okay.

NARRATOR

They've recently done this with green fluorescent protein and fruit fly brains, which are less dense than ours.

PIERIBONE

So we need a protein that can go from dim to bright very quickly-- up, down, up, down, up, down-- to be able to follow these rapid transitions in electrical signals that we see in a cell.

NARRATOR

They then insert the glowing, voltage-sensitive protein into the flies. Under a special microscope, they can now watch as the flies think. Each time a neuron fires, the voltage changes, and so does the intensity of the glow.

PIERIBONE

To be honest with you, it's absolutely exciting to sit there and see a brain of an organism as the animal is thinking and watching it as it happens in real time.

NARRATOR

Unlike conventional scans, which measure activity across the entire brain, these flashes of light and color are some of the first direct images of electrical activity of individual neurons in a living, thinking brain, the basis of all behavior. Here's a fly being presented with a new smell. When going to sleep. When waking up. So far, the scientists have managed to image just a handful of neurons, a far cry from the 86-odd billion powering the human brain. But to Vincent, it's a profound step on the way to decoding how our brains govern our actions and conjure our thoughts.

PIERIBONE

Ultimately, that nerve cell activity is what gives us consciousness, memory, behavior, personality. Everything we do, it derives from that, so not understanding that is an absolute crime. And now with these probes that we're developing, we can now start to record every single neuron.

NARRATOR

To map anything more sophisticated than a fly, though,

Vincent is missing one key ingredient

those red fluorescent proteins. Fly brains are tiny and relatively transparent. Green fluorescent protein can penetrate them easily. But for bigger, more complex brains, scientists still need infrared.

PIERIBONE

Again, the goal of the far red is to have this ability to shine far red light, which penetrates through tissue better. So red is just really what everybody wants.

NARRATOR

It'll take years to fish through the hundreds of samples recovered in the Solomons. They're still working to purify the bright red coral that had them so excited on the ship. But one of the fish they picked up, a species of lizardfish, seems to fluoresce far red light quite well. The team has just determined that a single protein is responsible for the red fluorescence, and Vincent hopes to soon engineer it to light up neurons.

PIERIBONE

These tools that we're developing and other labs are developing are giving us a chance to witness those things we've wanted to witness since neuroscience began 100 years ago, but we're for the first time being able to see the process as it happens.

NARRATOR

And the promise of glowing creatures isn't limited to the brain. Around the world, other researchers are harnessing them in many different ways. In Florida, Edie Widder is using bioluminescent bacteria to shine a light on pollution. Toxins in polluted water happen to interfere with the bacteria's ability to produce light.

WIDDER

The more polluted it is, the more the light dims, so you get a relative measure of toxicity.

NARRATOR

By taking sediment samples in threatened estuaries, mixing it with the bioluminescent bacteria and measuring the light they give off, the technique provides a quick and cost-effective way to detect pollution. Elsewhere, scientists have modified firefly genes in the hopes of creating bioluminescent trees that could one day light up cities. Another lab has co-opted marine bacteria to produce an electricity-free lamp. And it might not be a cure for cancer or a map of the brain, but one company has made biofluorescence available to the masses, with green fluorescent ice cream, a mere $220 or so per scoop. As for Vincent, David, and John, they're already planning a return trip to the South Pacific and other remote stretches of our planet to search for new dazzling critters, both bioluminescent and biofluorescent.

GRUBER

We humans can't create these from scratch. We need to go to the corals, we need to go to these fishes to find these molecules that we can then illuminate the inner workings of ourself. To me, I think that's just, you know, incredibly cool.

NARRATOR

We're only just beginning to see the light of this mysterious hidden world. Who knows what illuminating wonders await? But thanks to those alluring creatures of light, the future of at least one species, our own, may be an enlightened one. To order this program on DVD, visit ShopPBS or call 1-800-PLAY-PBS. Episodes of "NOVA" are available with Passport. "NOVA" is also available on Amazon Prime Video.