Living fossils: Who you calling primitive?

[Red pandas](. Horseshoe crabs. Ginkgo trees. Crocodilians. They’ve all been called living fossils, species that appear to have changed very little since their now-fossilized ancestors lived, or that have no close living relatives. Such a wide range of plants and animals can be described as such that it’s hard to grasp why it might be useful, other than as a jumping off point for[internet-ready lists]( of the [most amazing living fossils in the world](. “The term ‘living fossil’ is an imperfect concept, which has caused much consternation among paleontologists and biologists,” Matt Ransford [wrote in 2008 for Popular Science](. “The concept is an informal window into the past, a way for us to consider species as they may have been millions of years ago by observing their modern descendants.” Close examination of the DNA of tadpole shrimp, coelacanths, and tuataras have revealed that they have actually changed significantly over the eons. This has led [some scientists to suggest that we abandon the term](. Not only are living fossils not really a thing, they argue, the concept deepens common misunderstandings about the way evolution works. So, living fossils—are they for real, or has our thinking on them evolved? 🐦 [Tweet this!]( 🌐 [View this email on the web]( [Quartz Daily Obsession] Living fossils February 06, 2020 Blasts from the past --------------------------------------------------------------- [Red pandas](. Horseshoe crabs. Ginkgo trees. Crocodilians. They’ve all been called living fossils, species that appear to have changed very little since their now-fossilized ancestors lived, or that have no close living relatives. Such a wide range of plants and animals can be described as such that it’s hard to grasp why it might be useful, other than as a jumping off point for[internet-ready lists]( of the [most amazing living fossils in the world](. “The term ‘living fossil’ is an imperfect concept, which has caused much consternation among paleontologists and biologists,” Matt Ransford [wrote in 2008 for Popular Science](. “The concept is an informal window into the past, a way for us to consider species as they may have been millions of years ago by observing their modern descendants.” Close examination of the DNA of tadpole shrimp, coelacanths, and tuataras have revealed that they have actually changed significantly over the eons. This has led [some scientists to suggest that we abandon the term](. Not only are living fossils not really a thing, they argue, the concept deepens common misunderstandings about the way evolution works. So, living fossils—are they for real, or has our thinking on them evolved? 🐦 [Tweet this!]( 🌐 [View this email on the web]( By the digits [1:]( Times Charles Darwin mentions “living fossils” in On the Origin of Species [>20 years:]( Lifespan of a horseshoe crab [4:]( Days a horseshoe crab can survive out of the water [100 years:]( Time that elapsed between the discovery of the platypus and the realization that they lay eggs [13 hours:]( Time each day red pandas devote to finding and eating food, mostly bamboo leaves [18 inches (46 cm):]( Length of a red panda tail [2,575 ft (785 m):]( Underwater depth limit for chambered nautiluses; any deeper and their shells implode from the pressure [5,000:]( Ticks an adult possum can eat in a single summer [2:]( Vaginas a female possum has Wikimedia Commons Origin of Species story Blame it on Darwin --------------------------------------------------------------- The whole notion of living fossils is based on a passage from On the Origin of Species. In reference to some freshwater dwelling species including the platypus and the lungfish, [Charles Darwin writes]( “These anomalous forms may almost be called living fossils; they have endured to the present day, from having inhabited a confined area, and from having thus been exposed to less severe competition.” From there the idea that some organisms change less than others over time—whether because they have reached the apex of their form or encounter fewer selective pressures—took hold. The problem is, there’s no real scientific definition or criteria that gives the concept real meaning. “Although the idea of living fossils flourished after Darwin introduces the idea, it was never formally defined and was used as a catch all for apparently any organism that has an interesting fossil record,” [Mark Carnall writes in the Guardian](. A [2017 study from the University of Bristol]( of the tuatara, a [lizard-like creature]( found in New Zealand, claimed to have created a method of measuring the relative rates of change in morphology, the size and shape of organisms, over long periods of time. “Darwin’s wasn’t a testable definition,” [the study’s co-author, Tom Stubbs, told ScienceDaily](. “By using modern numerical methods we have now shown that living fossils should show unusually slow rates of evolution compared to relatives.” In contrast, a [2008 study of tuatara DNA found that they display an unusually fast rate of molecular change](. In their report, the team from Griffith University in Australia wrote, “Given this high rate of molecular evolution, the stable morphology of tuatara over tens of millions of years is remarkable.” Quotable “Crocodiles and snapping turtles are often called living fossils, more on the basis that they look ‘prehistoric’ than any scientific grounds.” —[Mark Carnall, writing in the Guardian]( Giphy Million-dollar question Why does it matter what we call them? --------------------------------------------------------------- [Evolution is a far more subtle concept]( than we generally imagine, and the notion of living fossils implies that some organisms simply don’t change. At all. Even if it’s not outwardly observable, species are constantly changing on the molecular and genetic level. Selective pressure, who breeds with whom and which genes get passed on, is one reason. Genetic drift is another. It’s the result of [discrete, event-driven outside pressures that eliminate part of a population by chance]( with no opportunity to adapt or change in response. Think [giant forest fires]( an oil spill, or sweeping land clearance projects. [Species do not stop evolving once they’ve become “perfect,”]( and while some species may evolve over time to better thrive in their environment, the process of evolution is not a steady march of progress toward an endpoint. [Scientific literacy is a necessary skill]( for fully engaging in civic life, whether you’re considering climate policy or [where to invest your money]( and there are long lists of basic scientific concepts with robust definitions [that get misused in everyday life and in the media]( on a regular basis. Overly broad, non-specific concepts like living fossils can detract from our collective understanding of science and scientific language. Giphy pop quiz Which of the following is NOT considered a living fossil? NautilusesPandasTadpole shrimpAardvarks Correct. Red pandas are considered living fossils because they are not related to any other living species, including the black and white bear we call a panda, which has no relation to the red panda, and is not a living fossil, either. Incorrect. If your inbox doesn’t support this quiz, find the solution at bottom of email. Explain it like I’m 5! What even is a living fossil? --------------------------------------------------------------- There are way too many definitions for the term to be scientifically meaningful. Here are a few ways to get living fossil status: 👴 Be very old. Organisms with long fossil-record histories like horseshoe crabs and coelacanths are often called living fossils. 🚷 Don’t ever change. Organisms change at different rates, whether that’s on the molecular or morphological level, but when species look very much the same as their fossilized relatives, like tadpole shrimp and ginkgo biloba, they’re often called living fossils. 😞 You’re a loner. Red pandas, aardvarks, and opossums are all singular—they have no close living relatives and their closest ancestors died out a long time ago. 🐊 You’re “primitive.” Animals like sharks, crocodiles, and horseshoe crabs that seem like they’re throwbacks to the prehistoric world may have long lines of ancestors, but don’t we all? Have a friend who would enjoy our Obsession with Living fossils? [ [Forward link to a friend](mailto:?subject=Thought you'd enjoy.&body=Read this Quartz Daily Obsession email – to the email – AP Photo/Steve Helber, File Species of Interest Horseshoe crabs --------------------------------------------------------------- Often held up as examples of living fossils, horseshoe crabs have existed in some form for over 450 million years. As such, [Cool Green Science called them “the world’s most successful animal]( They survived the [Great Dying]( but they may not survive the [Anthropocene era](. The blood of the horseshoe crab is extremely valuable. Not just because of its unique cerulean hue that comes from the way [oxygen binds to the copper in their blood]( but because it saves lives every single day. It’s used to make tests that detect bacterial toxins in pharmaceutical products and medical devices. Horseshoe crabs are harvested, transported to labs where about a third of their blood is drained, then dumped back in the ocean. As demand for their blood had grown, their habitat has shrunk. Horseshoe crab blood works because it’s so old. Its immune system is primitive but efficient, and its simplicity is a feature—rather than fight an infection, it immediately clots, producing an “[instantaneous, visible reaction]( to endotoxins.” And what’s worked so well to preserve the creature is now a liability for it. [Read the Quartz Obsession on horseshoe crabs]( Fun fact! Creationists hold living fossils up as “evidence” that evolution is not real, and that the world [was recently created](. Watch this! He’s that guy --------------------------------------------------------------- Blake de Pastino, one of the hosts of the science show Eons, which traces the history of life on Earth, explains why the concept of living fossils isn’t just intellectually flimsy, it also impedes our understanding of evolution. take me down this 🐰 hole! If you’re looking for something to obsess over rather than the opaque category of living fossils, try [EDGE species]( (Evolutionary Distinct and Globally Endangered), like the [Plains-wanderer]( the [Cuban solenodon]( the [largetooth sawfish]( and the [Roti Island snake-necked turtle](. Giphy poll Misunderstandings of which concept bug you the most? [Click here to vote]( EvolutionProbabilityArtificial intelligence 💬 let's talk! In yesterday’s poll about [Kali]( 32% of you said you most admire Athena, while Kali came in second at 29%. 🤔 [What did you think of today’s email?](mailto:obsession%2Bfeedback@qz.com?cc=&subject=Thoughts%20about%20Living%20fossils%20&body=) 💡 [What should we obsess over next?](mailto:obsession%2Bideas@qz.com?cc=&subject=Obsess%20over%20this%20next.&body=) [🎲]( [Show me a random Obsession]( Today’s email was written by [Annaliese Griffin]( and [Stevie Borrello]( and produced by [Tori Smith](. [facebook]( The correct answer to the quiz is Pandas. 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