Imagine plunging into the abyss of our planet's deepest oceans, where sunlight dares not venture, and yet encountering a mesmerizing, ethereal light show that defies the shadows. That's the captivating world of bioluminescence—a natural phenomenon that's been lighting up the dark for far longer than most people realize. And here's the hook: a groundbreaking study reveals this glow evolved over 500 million years ago, rewriting our understanding of life's ancient adaptations. But here's where it gets controversial—could this trait have sparked evolutionary battles in ways we're just beginning to unravel?
Bioluminescence is an extraordinary trait that allows certain living organisms to generate their own light through chemical reactions, serving a variety of clever purposes across the animal kingdom. From luring unsuspecting prey to warding off predators or even communicating with mates, this self-made illumination has developed independently in at least 94 separate instances throughout Earth's history, as detailed in a comprehensive review (https://onlinelibrary.wiley.com/doi/full/10.1111/brv.12672). Picture creatures like the ghostly deep-sea anglerfish or bizarre jellyfish that light up the void, turning the ocean's darkest realms into a spectacle of living lanterns (https://www.sciencealert.com/ghostly-creature-deep-in-the-ocean-is-like-nothing-weve-seen-before).
Researchers have now pinpointed the earliest known origins of this glowing superpower to a group of ancient corals known as Octocorallia (https://en.wikipedia.org/wiki/Octocorallia), thriving in the murky depths during the Cambrian period, approximately 540 million years ago. For context, the Cambrian era was a time of explosive biodiversity, when multicellular life forms were just starting to diversify in the seas, giving rise to the first complex ecosystems. This discovery doubles the age of the previous record holder—a diminutive deep-sea crustacean from about 267 million years ago (https://academic.oup.com/sysbio/article/72/2/264/6671865), showcasing how bioluminescence predates many familiar life forms.
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Marine biologist Danielle DeLeo, the lead author from the Smithsonian Institution, explained their motivation in an interview when the study was released in April last year (https://www.eurekalert.org/news-releases/1041494): 'We set out to determine when bioluminescence first appeared, and octocorals represent one of the oldest animal groups known to possess this trait. The big question was: exactly when did they acquire this capability?'
Octocorals are truly intriguing beings. Like their coral cousins, they consist of tiny polyps—individual organisms—that band together to create colonies, often anchored to a structure built from their own hardened secretions. What sets octocorals apart, named for the eight-pointed symmetry of their polyps, is their more flexible, softer skeletons compared to the stiffer builds of related corals. And some species among them glow with bioluminescence, though it's a bit enigmatic—they only light up when agitated or disturbed. Scientists speculate this might serve as a clever bait to draw in prey, or perhaps alert larger predators to feast on the smaller fish that nibble and harm the coral, creating a sort of indirect defense mechanism.
Given that corals rank among the planet's most ancient living inhabitants, and octocorals are recognized for their glowing abilities, DeLeo and her team reasoned these creatures offered the ideal vantage point for tracing bioluminescence's primordial roots. The foundation for their work was a meticulous octocoral evolutionary tree, crafted in 2022 using genetic data from 185 different octocoral groups (https://ssbbulletin.org/index.php/bssb/article/view/8735). Building on this, they analyzed lineages of known glowing octocorals gathered through fieldwork by experts Manabu Bessho-Uehara from Japan's Nagoya University and Andrea Quattrini of the Smithsonian Institution.
Their underwater expeditions uncovered previously undetected bioluminescence in five additional octocoral varieties—a revelation that fueled their use of a technique called ancestral state reconstruction. As Quattrini described (https://www.eurekalert.org/news-releases/1041494), 'By identifying which modern octocoral species exhibit bioluminescence, we apply statistical methods to estimate the likelihood that their extinct ancestors shared this trait. The greater the number of living species with the common characteristic, the stronger the evidence that earlier generations likely possessed it too.'
Employing multiple statistical approaches, the researchers consistently arrived at the same conclusion: bioluminescence originated in the shared ancestor of all octocorals around 540 million years ago. This era coincided with the presence of marine invertebrates equipped with light-sensing eyes, hinting at early interactions between species—perhaps a luminous arms race in the ancient seas. Such timing could illuminate why this ability developed in the first place, potentially as a tool for survival in a competitive, light-deprived environment.
For a fascinating side note, check out how scientists are now engineering glow-in-the-dark succulents in the lab, bringing a touch of bioluminescence to your garden (https://www.sciencealert.com/scientists-have-created-glow-in-the-dark-succulents-and-we-want-one).
And this is the part most people miss: if the original octocoral ancestor, from which thousands of species descend today, was bioluminescent, why is it that only a handful retain this feature now? How did so many lose it over eons? That's the pressing question ahead, and answering it might reveal hidden secrets about the bizarre food webs and ecological dynamics of the Cambrian oceans—think of it as a paleontological puzzle that could challenge our views on evolutionary loss.
The findings were detailed in a paper published in Proceedings of the Royal Society B Biological Sciences (https://royalsocietypublishing.org/doi/10.1098/rspb.2023.2626). An earlier version of this piece appeared in April 2024.
Don't forget—subscribe to our free Spark newsletter today (https://www.sciencealert.com/spark-into-space-comp?utmsource=promospace) and you could win a $10,000 vacation featuring a bioluminescent night kayaking adventure! The contest ends on December 11, 2025, at 11:59pm ET. Find all the details here (https://www.sciencealert.com/spark-into-space-comp?utmsource=promospace).
What do you think about this ancient glow? Is bioluminescence evidence of nature's ingenuity, or could it be a controversial relic of forgotten evolutionary conflicts? Do you believe the loss of this trait in most octocorals suggests it was more of a burden than a benefit in modern times? Share your opinions and theories in the comments—we'd love to hear your take!
