what is life? it’s one of those questions that sounds simple until you try to answer it. philosophers have wrestled with it for centuries, scientists have chased it through microscopes and telescopes, and most of us, at some point, have stared at a starry sky or a buzzing beehive and wondered what makes the whole show tick. the urge to define life—to box it up in a neat sentence or two—is strong. but what if that urge is leading us astray? what if life, like some cosmic jazz riff, resists being pinned down by definitions? in this post, i’m diving into why our obsession with defining life might be a wild goose chase and sketching a different path forward—one that leans on exploration, not answers. buckle up; it’s going to be a thoughtful ride with a few twists.
why definitions miss the mark
defining life scientifically is one of those challenges that sounds simple until you dig deeper. let’s start with the obvious: definitions are tidy. they’re like the label on a jar of pickles—short, snappy, and meant to tell you exactly what’s inside. in everyday life, that works fine. call a bachelor an unmarried guy, and you’re good to go. but when it comes to something as sprawling and slippery as life, definitions start to feel like trying to catch a river in a teacup. the problem isn’t just that life is complicated—though, holy moly, it is. it’s that definitions are about language and concepts, not the messy, real-world stuff we’re trying to understand.
imagine you’re a scientist in the 1600s, pre-telescope, pre-microscope, trying to define a star. you might say it’s a twinkling light that moves across the sky. sounds reasonable, right? but then Galileo swings by with his fancy optics, and suddenly you’re staring at a giant ball of plasma that doesn’t “twinkle” at all—it just looks that way from Earth. your definition wasn’t wrong so much as it was stuck in what you could see and think at the time. life’s like that, only worse. we’re not just limited by our tools; we’re limited by having only one example to work from: Earth’s biosphere. every bacterium, tree, and TikTok-dancing human shares a common ancestor, a kind of cosmic great-grandma called LUCA (last universal common ancestor, for the jargon fans). that’s one data point. try building a universal theory of anything—stars, gravity, or even pizza—based on a single case, and you’re in for a rough time.
here’s where it gets tricky. scientists love to throw out definitions of life anyway. some say life is anything that reproduces and evolves, like Darwin’s greatest hits on repeat. others point to self-organization—think of a cell keeping its act together despite chaos. there’s even a crowd that swears by metabolism, the chemical hustle that keeps organisms humming. these ideas aren’t dumb; they’re grounded in what we see around us. but grounding a definition in Earth life is like defining music based only on Beyoncé’s discography. sure, it’s a banger, but what about jazz, or throat-singing, or whatever aliens might be vibing to on Proxima Centauri? we don’t know what we don’t know, and that’s the rub.
philosophically, definitions have their own baggage. back in the day, folks like John Locke thought words like “gold” or “water” meant whatever concepts we attached to them—shiny yellow stuff or wet clear liquid. but then along came thinkers like Hilary Putnam, who dropped a philosophical mic with his Twin Earth thought experiment. picture a planet where “water” looks and acts like H₂O but has a different chemical makeup, say, XYZ. same concept, different stuff. suddenly, it’s clear that what we mean by a word doesn’t always match what’s out there in the world. if life is a natural kind—a category carved out by nature, not human whims—then our concepts of it might be way off base. definitions, whether they’re old-school or dressed up as “theoretical” guesses, risk locking us into our current ignorance.
and let’s not kid ourselves: our ignorance is real. biochemists have shown that life’s building blocks could’ve been different. Earth life uses about 20 amino acids to make proteins, but there are over 100 possibilities out there. DNA and RNA? they could’ve rolled with different sugars or bases. even the way life codes information—those triplet codons—isn’t set in stone. it’s like finding out your favorite video game could’ve had a totally different rulebook and still worked. all this suggests that Earth life might be a quirky outlier, not the gold standard. so when we define life based on what we know, we’re not just guessing—we’re guessing with blinders on.
chasing anomalies, not answers
so, if definitions are a bust, what’s the play? here’s where I’m going to pitch something a bit radical: stop trying to define life and start hunting for weirdness. call it the anomaly approach. instead of looking for stuff that fits our checklist for “alive,” we should be sniffing out systems that make us go, “huh, that’s freaky—but kinda lifelike.” it’s less about nailing down what life is and more about stumbling across what it might be. this isn’t as flaky as it sounds; it’s how science often moves forward, from Newton spotting apples falling to Einstein pondering light’s quirks.
anomalies are the universe’s way of winking at us. they’re things that look familiar enough to grab our attention but strange enough to mess with our assumptions. think of the Viking missions to Mars in the ‘70s. NASA sent landers armed with experiments designed to spot life, based on a metabolic definition—think chemical reactions like those in Earth microbes. one test, the labeled release experiment, got spicy. Martian soil, fed a nutrient broth, started spitting out radioactive CO₂, like it was hungry. score one for life, right? but then things got weird. heat the soil, and the reaction stopped—classic biology move. but feed it more nutrients, and… nada. worse, leftover CO₂ vanished, like the soil was playing hide-and-seek. scientists scratched their heads. it looked alive, then it didn’t. instead of calling it a puzzle worth solving, they leaned on their definition and said, “nah, must be some funky chemistry.” case closed. or was it?
that’s the trap of definitions—they make us too quick to judge. an anomaly approach would’ve kept the Viking results on the table, prodding us to dig deeper. maybe Mars has life that doesn’t play by Earth’s rules. maybe it’s a “shadow biosphere” right here on our planet, hiding in plain sight because our PCR tests and microscopes are tuned to LUCA’s descendants. the point is, we won’t know unless we look for stuff that doesn’t fit. anomalies aren’t answers; they’re invitations to rethink everything.
how do you hunt for anomalies? you start with what you know but treat it as a loose guide, not gospel. pick features of Earth life—say, complex carbon chemistry, or patterns that scream “not just physics”—and use them as clues, not dealbreakers. these aren’t definitions; they’re fishing nets, designed to catch anything that swims close enough to “alive” to warrant a second glance. and you don’t limit yourself to universal traits. maybe some obscure bacteria in a deep-sea vent make crystals no rock can mimic. that’s a clue worth chasing, even if it’s not true of all life. the goal is to find systems that echo life in one way but surprise us in others.
take ALH84001, that Martian meteorite found in Antarctica. it’s got tiny magnetite crystals that look eerily like ones made by certain Earth bacteria. back in the ‘90s, some scientists shouted “Martian fossils!” because no known non-living process could make crystals that pure and prismatic. skeptics pushed back, saying abiotic chemistry might explain it. the jury’s still out, but that’s the beauty of anomalies—they spark debate, not verdicts. if we’d been hunting anomalies instead of “life,” we’d have sent more probes to Mars to settle the score, not moved on to the next shiny object.
this approach isn’t just for space. synthetic biology—folks trying to whip up life in labs—could use a dose of anomaly-chasing too. instead of aiming for cells that check all the boxes (reproduction, metabolism, yadda yadda), why not tinker with systems that do something lifelike but bizarre? maybe a chemical soup that self-organizes in ways physics can’t explain. maybe it’s not “life,” but it’s close enough to teach us something new. the trick is staying open to the unexpected, not boxing ourselves in with preconceptions.
why this matters (and why it’s okay to wait)
i get it—telling people to ditch definitions and chase weirdness feels like saying, “don’t solve the puzzle; just collect more pieces.” it’s frustrating, especially when we’re wired to want answers. but here’s the thing: rushing to define life doesn’t just risk getting it wrong; it risks blinding us to what’s out there. the Viking mission might’ve missed Martian life because it was too married to Earth’s playbook. synthetic biologists might be spinning their wheels chasing familiar patterns when a wilder idea could crack the code. even philosophers, bless their wordy hearts, get stuck debating concepts when they could be asking what new discoveries might upend the game.
patience is key. science doesn’t always move fast, and that’s okay. it took centuries to figure out water was H₂O, and even then, it wasn’t just one “eureka!” moment—it was a slog of experiments, arguments, and better tools. life’s a tougher nut to crack because we’re not just dealing with molecules; we’re grappling with a phenomenon that might look totally different elsewhere. a universal theory of life—one that covers Earth, Mars, and whatever’s brewing in Europa’s oceans—needs more than one example. it needs anomalies to challenge our assumptions and point us toward the truth.
there’s a practical upside too. hunting anomalies could juice up NASA’s search for extraterrestrial life. instead of sending rovers with rigid checklists, we could design missions to flag anything that smells faintly lifelike—odd chemical cycles, funky energy flows, or structures that don’t scream “just a rock.” it’s not about proving life’s out there; it’s about finding candidates worth studying. same goes for Earth. if there’s a shadow biosphere—life that doesn’t share LUCA’s DNA—our best shot at finding it is looking for systems that mimic life in some ways but flip the script in others.
philosophically, this approach keeps us honest. it reminds us that our concepts aren’t the world—they’re maps, and maps can be wrong. by focusing on anomalies, we’re admitting we don’t have all the answers and letting the universe surprise us. that’s not just science; it’s a mindset. it’s saying, “i don’t know what life is, but i’m stoked to find out.”
so, what is life? i’m not going to pretend i’ve cracked it. nobody has. but i’d bet my coffee stash that we’ll get closer by chasing the strange than by circling back to definitions. life’s out there, doing its thing, whether it’s in a Martian crater, a lab flask, or some corner of Earth we’ve overlooked. let’s go find it—not by deciding what it is, but by letting it show us what it can be.
reference:
this article largely draws on the insights and data from that piece: cleland, carol e. “life without definitions.” synthese 185, no. 1 (2012): 125–44.
