These Creatures Were Darwin's Greatest Enemy

don't forget our 2023 calendar featuring some of our favorite main characters of paleontology from classic eons episodes is available now at complexlycalendars.com this is a barnacle chances are you've seen one before they're found in virtually all Marine environments stubbornly attached to any surfaces they can find from rocks and boats to whales and turtles they may not look like much but beneath that shell lies an evolutionary mystery one that stumped the biggest names in natural history for over a hundred years some of the most influential biologists of their day grappled with the challenge of working out what they actually are and where they fit in the Tree of Life only to be proved totally wrong others were almost broken by the attempt including Charles Darwin who embarked on an eight-year long personal side quest to figure them out by year 6 he wrote to a friend I hate a barn article as no man ever did before in the end though the mystery of the Barnacle would help him figure out part of the mystery of life itself so what's the deal with Barnacles how did they resist classification by some of the biggest names in natural history and why did they make Darwin so mad [Music] first a quick Barnacle 101 this group of marine animals known scientifically as the siripedes is diverse ancient and wide-ranging today there are over a thousand known species found across the world they generally exist as immobile filter feeders that stay attached to surfaces and waft Plankton and food particles into their mineralized shells though some species live as parasites of other animals and we know from the fossil record that they've been around for a very long time definitive shelled Barnacles first show up in the mid-carboniferous period around 320 to 330 million years ago though some are argued to be even older and we know of more than 400 extinct species mostly from fossilized shell fragments but even though they've been around for hundreds of millions of years and are common today for much of History we got them totally wrong in the mid 1700s Carl Linnaeus often considered the father of modern taxonomy aka the study of classifying living things was among the first to try and place the group he saw Barnacles as being similar to some Marine mollusk species that also have mineralized shells and don't move around much like oysters clams and mussels which Fair so he put Barnacles in the mollusk group too then in the early 1800s the French naturalist George cuvier sometimes called the father of paleontology also turned his attention to Barnacles he noted that beneath their shell they seemed to share some traits with another animal group called The articulates which included things like Crustaceans and insects in the end though when he published his most famous work in 1817 he also decided to classify Barnacles as mollusks but then in 1830 British naturalist William Thompson entered the chat with a pretty bold claim those two world-renowned naturalists had been fooled see Barnacles go through a free swimming stage as juveniles before they stick themselves to a surface for good Thompson observed this and realized that during part of their development juvenile Barnacles were pretty much identical to a juvenile stage of crustaceans so he figured that they must actually be Crustaceans too which may makes them relatives of shrimp crab and lobsters they just happen to have an adult stage that resembles mini mollusks it might not sound like much but this was a radical reinterpretation of what Barnacles actually are it's rare in Zoology for a group of common macroscopic living animals to be reclassified at one of the higher levels of the nested taxonomic system that we use the ones above family genus and species the higher up the taxonomic ranking that you go the more fundamental the differences get so it's usually pretty obvious which group a living organism belongs to at those higher levels and as a result the higher the level of a proposed reclassification the more profound its implications are for our understanding of the nature of a thing and this was one example of a deep and significant shift of our understanding mollusks and Crustaceans aren't even part of the same animal phylum the rank right below Kingdom which tells you if a thing is an animal or a plant it was the equivalent of scientists suddenly announcing that birds are actually a type of starfish the scale of this sudden reanalysis is partly what triggered Charles Darwin to join The Fray in 1846 Barnacles had previously captured his attention during his voyage around the world on the HMS Beagle when he came across some species that left an impression on him so when they became a hot Zoological topic following Thompson's radical proposal Darwin probably saw it as a great opportunity if he could bring some order to this messy and confusing Barnacle situation it would help him puzzle through some of the evolutionary Concepts he'd begun to think about like the approach of trying to group organisms on the basis of common descent from a shared ancestor by comparing their anatomical features plus if he could develop some expertise around a poorly understood group like Barnacles it would help him build his scientific credibility before revealing his ideas about natural selection to the world how could it be a quick side quest that would take a year or two Max in fact it took eight over those long years he did make several major insights into the diversity and biology of both living and fossil Barnacles and in the process he became recognized as one of the world's leading Authorities on them but the strain of intensively studying such a weird group of animals was almost too much for him to take at times in one letter he wrote I make no perceptible progress and I groan under my task and on what must have been a particularly rough day during the Barnacle years he said confound and exterminate the whole tribe I can see no end to my work despite being so frustrated by these creatures that he found himself wishing that they never existed of feeling familiar to many graduate students Darwin did eventually see the end of his work his detailed analysis of modern and extinct species is still important to the study of barnacles today he helped confirm Thompson's radical reclassification of barnacles as a branch of the crustacean family tree and they've stayed there ever since today we know them as a lineage of crustaceans that embarked on a totally different evolutionary Journey from any other members of the group while they did keep some crustacean traits like the free swimming larval stage cuticles made of chitin and segmented bodies they also developed some distinctly uncrustation traits too for example their mineralized external shells and a mobile adult stage were they basically cement themselves to a surface these two features are typical of some mollus groups but aren't seen in any other Crustaceans and it seems that the reason this evolutionary convergence with mollusks fooled some of the biggest old-timey names in biology is that it runs particularly deep right down to their DNA in 2022 researchers in China published a new study in which they compared barnacle and shelled mollusks genomes to look for signs of convergent evolution between them at the molecular level despite having been on distinct evolutionary Journeys for hundreds of millions of years the researchers found several instances of genetic convergence for example they independently duplicated many of the same families of genes often having to do with shell formation and some of the convergently evolved genes were only seen in the two groups and not in either of their closest relatives in fact at the time the paper was published it was the most distant reported example of two animal groups showing genome-wide convergent evolution so it understandable that barnacle's baffled biologist for so long their physical convergence with mollusks is backed up by an equally impressive level of genetic convergence with them too and this is something that none of those big names could have ever come up with let alone investigated seeing as they all lived before anything was really known about genetics but at least in the case of Darwin though the struggle to understand the Barnacles was long and painful it turned out to be well worth it not just because the effort built him some valuable scientific street cred but also because in all that stress and confusion came occasional glimmers of evolutionary Enlightenment for example as he dissected described and compared every Barnacle specimen he could get his hands on he was struck by how much variation he saw even between individuals of the same species this realization about the extent of variation between individuals would later become a key pillar of his theory of evolution by natural selection variation is the raw material material for evolution it's what natural selection acts on favoring some variants relative to others in a population because of the survival and reproductive advantages they offer so by studying Barnacles in such detail for so long Darwin gained a deep appreciation of the subtleties of biological variation available for natural selection to act on and working on this enigmatic ancient and diverse group allowed him to test and refine critical aspects of his revolutionary ideas while it seemed like just a detour from his main project in the beginning in the end we owe a lot of our understanding of the natural world to Darwin's frustrating work on the mystery of the barnacle [Music] I can see no end wait I gotta do it like I can see no end to how awesome this month's eontologists are Gail Brown Juan M Jackson Weiss Melanie lamb Carnival Annie and Eric Higgins John Davidson ing Colton chase our Shambo and Jake Hart by becoming an eon eye at patreon.com eons you can get fun perks like submitting a joke for us to read here's one from Joey letsinger why did the plesiosaur cross the ocean to get to the other tide that was great that was really cute and as always thank you for joining me in the Adam Lewis studio subscribe at youtube.com eons for more primordial ordeals foreign in my best Victorian man voice so bear with me by year six he wrote to a friend I hate the Barnacle as new man ever did before expressive Victorian pain of Darwin from deep within [Music]

Channel: PBS Eons

Views: 1,673,752

Keywords: barnacle, darwin, cirripedes, Linnaeus, Cuvier, mollusc, crustacean, arthropod, genome, dna, natural history, paleontology, biology, science, evolution, variation

Id: plYuvU2VZkE

Length: 11min 29sec (689 seconds)

Published: Tue Jan 10 2023