I was lying on my own surgical bed in my own surgical suite. Face down, back sliced open, hurting.

“Can you feel this?” My colleague asked as she cut a bit deeper.

Searing, horrendous pain.

“Fuck yes. My God, Aly, do you hate me?”

I’d kept the giant lipoma on my back far longer than I should have. It helped a lot of people over the years. Nervous patients come to my clinic all the time sweating buckets over whether they have the “Big C,” when all they have is a glob of fat under their skin.

I’d habitually turn around to show them: mine was bigger. They’ll be fine, but I’ll cut it out if they would like.

Many people would like, and I oblige.

But mine got to be the size of a grapefruit, right over my spine. Once it started setting off the detector at the airport and feeling like a pair of rolled up socks was stuck under my shirt all the time, I knew it had reached the end of its usefulness.

So a little chlorhexidine and a lot of lidocaine later, I found myself on my stomach, imagining each step as Dr. Yelich progressed.

Chitchatting about life and babies and—

“Dammit!”

The lidocaine wasn’t working. I was one of those patients.

Some people take double the normal amount of numbing. Some triple. A select few unfortunate people need quadruple.

I’m four times the fun.

And the only way to figure out you’re a 4x person instead of a 1x person is, unfortunately, to find out.

For me, a planned 40-minute surgery stretched to two hours, most of it spent numbing, testing, and numbing again.

So I had a lot of time to think about pain.

It was weird.

I knew I was in good hands, that Aly was helping me, and that I was in no danger. So I didn’t recoil. No jumping off the table. The lidocaine killed the pain but left plenty of pressure, so I could tell what she was doing. I knew exactly what my wound looked like and where she was cutting, grabbing, and pulling. I’ve seen this movie.

Just that sometimes my body would tell me that I was experiencing an emergency. Cut one area: nothing. Cut another: horrible.

The injury was objective, my experience wasn’t. And yet it was real.

A message I couldn’t ignore. I was being damaged, and I should do something about it.

And that meant politely asking my fellow dermatologist for more lidocaine, in every clever and silly way I could muster. I wasn’t angry or scared. I just really didn’t like the feeling, and it kept me from concentrating on asking about how things were going with her two kids.

In medical school we spent a whole day defining pain. Great. Tissue damage. Potential tissue damage, imagined tissue damage. Crossed wires, pinched wires, broken wires. Emotional pain. Emotional pain that becomes physical pain.

Nociception: Your nervous system detects something bad.

Pain: It feels bad.

Emotional pain: ?!?!?!

It’s complicated.

But why?

Sometimes your body wants to say, “Hey buddy, you stepped on a thorn. You should stop what you’re doing and examine your foot because if you don’t, you could get an infection and be left for dead by your hunter gatherer tribe.”

But our peripheral nervous system doesn’t speak English. Only urgency.

“HOLY SHIT, STOP RIGHT NOW!”

Ok, fine.

It certainly didn’t feel fair feeling the scissors deep in my back.

But really, I have no business complaining. I should feel it. I’m not supposed to be able to sit still through a procedure like that. It should hurt too much to ever agree to.

But we have lidocaine.

It gums up the little sodium channels that nerves use to bring news of injury and destruction.

Lidocaine keeps me in business.

And it decouples injury from response. You can see the wound, know it should hurt, and not feel it. Evolution didn’t bargain for that.

Finally, after about 90 minutes, Dr. Yelich finally got it.

“How about this?”

The pain melted away. Instant relief. I didn’t feel it again the rest of the procedure.

Like magic.

But later, my body remembered. I didn’t feel right for days after. My body knew it had been injured. A whole alphabet soup of inflammatory molecules telling me all sorts of nasty things about what happened.

But my mind remembered, too. I’ve thought about the pain more than seems reasonable. Whatever part of my brain that’s sending this message didn’t get the memo that I asked for all this.

That shit hurt. My body and my brain want me to know it.

Maybe that’s the point.

Nociception isn’t new. Nematodes move away from noxious stimuli. Same little bob and weave motion, highly stereotyped. Reflex. Nociception.

Pain?

Pain is more than reflex. It’s a signal that pokes us while we’re making other plans. An input we weigh against other variables. Something we remember later to help us make safer choices.

Sometimes pain wins. Other times we fight through it.

Notice a rock in your shoe on a hike, and you may stop and remove it. Grit your way through it, and you’ll get a blister. Next time, you may remove the rock sooner.

Notice a rock in your shoe while you’re running from a bear, and you’ll probably wait it out.

Break your leg while you’re running from a bear, and you need a new plan.

This isn’t uniquely human. Give a hermit crab a shock in its shell, and you can watch it calculate. Great shell? Crab takes more shocks. Crappy shell? Crab bails.

Offer a new shell to a crab who stuck it out. It’s quicker to make the switch.

It’s about computation. And memory.

Scissors in back? Extremely bad

Remove lipoma? Good

Aly Yelich? Safe

Jump off table? Bad idea

Ask for more lidocaine? Appropriate

Three weeks out now, the pain is pretty much gone but I still think about it. I find my mind wandering to the (very well-healing) scar on my back, wandering to the pain. Despite the intellectualization, despite the anesthesia, and despite me having performed that exact surgery hundreds of times, I’m still thinking about it.

The memory is doing what it’s supposed to.

My body’s way of saying, “What’d you do that for?”

“Daddy, why do mosquitoes bite?” A reasonable question from a freshly bitten toddler.

I’m in Northern California to see good friends and catch big trout on the McCloud River. I’ve been throwing little bits of hair and feathers into the river and doing my best impression of a mayfly. I’m not very good at it.

There are mosquitoes here, too.

“Because the mommy mosquito needs blood to lay its eggs.” I dabbed some triamcinolone on her.

“Why?”

“Because mommy mosquito can lay more eggs if she gets extra nitrogen, so she gets the raw materials to lay eggs from the giant vertebrates lumbering around.”

“Why?”

“Because the nectar she drinks is basically just carbohydrates.”

“Why?”

Dammit. Let’s write a story: mosquitoes, mayflies, and metamorphosis.

Gather ‘round, kids.

Baby mosquito is hungry, and she swims around in her tepid, still pool looking for food. She finds some dead leaves. Yum. She eats a protozoan. Double yum!

She grows bigger and bigger, until one day she gets very tired. So tired she wants to nap for days and days. So she curls up, partially dissolves into a living proteinaceous goo, tumbles around the water’s surface, and then miraculously reassembles herself into the flying bane of summertime recreation.

Reborn, she flies away, hungry all over again. She stops at a flower and drinks some nectar. Carbohydrates, yum! She flies some more and gets hungry. Time to refuel. More nectar. More carbohydrates. Yum?

Then she does the nasty.

Then, a new hunger. More nectar? Nope. Carbohydrates don’t solve this problem. She doesn’t need fuel. She needs ingredients.

Amino acids. Protein. Raw ingredients for eggs. She doesn’t have teeth to eat other bugs. Just a hypodermic needle.

It’s why I bring triamcinolone on every family outing.

Humans like to think of life cycles as an animal slowly becoming larger and more complete. Kids grow into adults. Adults reproduce. Adults die.

A larval insect must be the baby version of the true adult that comes next. Right? Nope.

Insects get to have two bodies. Two chances at an organism. Sometimes, the lifestyles are similar and make sense. Feed a bee larva so it can become an adult bee. Easy enough.

But sometimes it’s not so simple. The phases of life drift. One phase can be excellent at a job the other is terrible at. Sometimes the forms seem to have nothing in common.

Larval mosquitoes are eating machines. Bacteria, algae, protozoans, and whatever else they can scrounge up. Lots of raw ingredients to make an adult.

Yet the adults mostly eat nectar. Sugar keeps them flying, but males don’t accumulate much more raw material than they inherited from their larval form. They don’t get the massive protein infusion of a blood meal.

For many female mosquitoes, the inheritance puts a limit on the number of eggs they can produce. Hence the blood.

It gets weirder.

Those mayflies I’ve been imitating this week with hair and feathers tied onto fishhooks.

Most of them only have vestigial mouthparts, and they live for only a day or two. Sometimes only for hours.

Their nymph form can live for years, crawling on rocks under the water, slowly accumulating biomass and energy. Waiting for the right time, the right conditions.

Then, all at once, time to mate. The collective genome of the local mayfly population sprouts wings and makes a mad dash into the sky to propagate.

Up and away, the DNA flies, mates, and redeposits itself in the river.

They may as well be spores. Actually, that’s not quite right. The eggs are the spores. The adult mayflies are mushrooms.

The adults are spent. Husks. Debris on the water. Trout food.

They were never the main organism, just part of an extremely weird whole.

Metamorphosis isn’t just about growing an animal. It’s about allowing evolution to divide a life between different bodies.

One grows, another disperses. One eats, the other mates. One spends a year under water, the other an afternoon in the air.

Some second bodies can refuel and repair themselves. Dragonflies are ruthless eating and killing machines.

Others emerge with almost everything they’ll ever have. They’re born with fuses.

Mayflies have some of the shortest fuses of all. Sprout wings, mate, die.

Mosquitoes have found a way to lengthen the fuse. They drink nectar to fly farther. They drink blood to make more mosquitoes.

The mayfly spends its inheritance. The mosquito borrows yours.

Camping trip to Big Fork with the missus and our four-year-old unicorn addict. Lakeside wiener roast.

Pack the camper. Tires checked. Brake lights working. Sunscreen: you bet.

Wiener roast complete, we soaked in the sunset over the lake.

Mosquito. Another mosquito. And another.

Bug spray. Ugh, Dad fail. Screaming child, everyone inside.

As the hubbub subsided, I found a squished mosquito on my arm. Tiny. Delicate.

Ordinary.

Butterflies, bees, praying mantises, lice on your head. Wildly different, but all the same. Head, thorax, abdomen, six legs.

What gives?

We boast about an Earth awash in biodiversity, but something like a million insect species all hum the same basic tune. Stretch a wing, modify a leg, reshape a mouthpart. Solenopsis mcmullenbergensis.

Walk in the woods and it’s pretty much just insects and arachnids and millipedes.

Zoom out and the small stuff mostly has exoskeletons, and the big stuff mostly has backbones.

Beneath all the decorations lie only about three dozen surviving animal phyla, the deepest blueprints of the animal kingdom. Most of them are worms.

Why isn’t there more stuff?

Well, because sometimes bad things happen.

There used to be more stuff.

Life went bonkers during the Cambrian explosion. Animals made the leap from the tiny and undulating to the macroscopic and directional. New niches, new ways of living, new ways to bolt doodads onto worms.

Lots of them.

Diversity on a different scale. Not deciding how big and what color, but deciding things like what a mouth is and where it could go.

Then the bad thing. And another. And another.

A comet smashes. A mega-volcano erupts for a million years. The oceans lose their oxygen.

Tiny burrowing mammals survived the comet that killed the dinosaurs. Now we have giraffes.

Cull 90% of all species and let the survivors repopulate. Then do it over and over. Diversity doesn’t disappear. It just gets rebuilt from survivors. Variations on themes.

Survivors might inherit a fresh Earth, but they don’t inherit fresh genetics. The big decisions about things like how to build a mouth were made long ago.

Once a body plan is set, it’s incredibly hard to rewrite the blueprint. You can change the wallpaper, but some walls are simply load-bearing. Evolution gets hemmed in by its own past.

Ostriches and hummingbirds. Lice and butterflies. Mice and people.

If Earth had a more boring geological history, maybe there we’d still have more of those early experiments. Maybe we’d think about biodiversity differently. Bottleneck after bottleneck led us to a diverse world, rebuilt by the few who survived.

An alien coming to Earth may marvel that there are only a few kinds of animals. So many arthropods. So many vertebrates.

Maybe someday cockroaches really will inherit the Earth. Then give them a hundred million years.

Millions of species. All suspiciously similar.

I looked back at the mosquito on my arm. Ordinary.

Green. It calms the nerves. Put an anxious talking ape in a meadow and watch its blood pressure fall. Green brings life.

Plants are green because chlorophyll absorbs red and blue light. Simple.

Except the sun shines brightest in green light. Yet plants reflect it.

Why would plants evolve to throw away the strongest light?

Now that’s a question.

Look closely at the business end of a chlorophyll molecule and you’ll see a magnesium ion suspended in a rigid porphyrin ring, holding it together. It looks almost like a little net.

A photon slams into the ring, and an electron jumps to a higher energy state. A few nanoseconds later, the energy winds up in a chemical bond. Jackpot.

Now look closely at a heme molecule. The oxygen carrier in our blood.

Well I’ll be damned. Looks just like chlorophyll, except there’s an iron ion where the magnesium should be.

How?

Rewind 3.5 billion years.

Life, the very early kind, was figuring out metabolism. How do you make a reliable copy of DNA? That kind of stuff.

That’s about the time we invented porphyrins. Little rings of carbon and nitrogen made of littler rings of carbon and nitrogen that are great at passing electrons around. They have little gaps in the center that are great at holding a metal ion in place. Energy in motion.

The metal tunes the electron cloud. Different metal, different properties. Magnesium makes chlorophyll. Iron makes heme. Cobalt, vitamin B12. And so on.

So plants are green because early bacteria repurposed a molecular scaffold it was already using for other things. They just slotted in a different ion.

Makes you wonder about other metals. Other molecular mechanisms. Other planets.

Surely alien plants would use different molecules. Different pigments. Purple forests beneath red suns.

Maybe.

In 1996, we found a bacterium living in extremely acidic environments that uses zinc in its chlorophyll instead of magnesium. That’s odd, until you realize that “extremely acidic” also means “extremely different.” The bacterial chlorophyll does exactly the same thing, just tuned to a different environment. Color? Green. The mechanism is the same, but the metal is different.

That makes sense, though. Acidiphilium rubrum’s ancestors probably had chlorophyll and just adapted it to a different environment.

Let’s get weirder.

A giraffe is impossibly complicated. But the building blocks that made it are not. The Krebs Cycle runs by popping atoms on and off molecules only four or five carbons long.

Porphyrins aren’t that hard to make. Run electricity through a beaker containing gases thought to resemble early Earth, and out fall porphyrins. And other goo that life uses.

Other planets are made of atoms, too. Carbon is carbon. Nitrogen is nitrogen. The same physics builds chemistry there as it does here. Porphyrins are simple on other planets, too.

Every evolutionary problem has a design space and a set of starting conditions. Move an excited electron. Hold a metal atom. Don’t fall apart in water. How many simple organic molecules can actually do all three?

Physics constrains chemistry.

Chemistry constrains biology.

Evolution searches what’s left.

Plants reflect the most abundant light from our sun.

Maybe other suns, too.

We spend a lot of time wondering how strange alien life might be. We spend far less time wondering how physics may force it to resemble our own.

Maybe green forests aren’t an accident. Maybe they’re waiting to be discovered.

What I’m reading: Wonderful Life by Stephen Jay Gould.

What am I even doing?

Just a few minutes ago I walked over to my office under the observatory dome to write an essay. I looked up at the silver monstrosity in the front yard and thought, “Why am I doing this?”

I don’t know. I like outer space. I like thinking deep thoughts. I like connecting dots. I like sharing wonder.

But what’s with the dome? The little essays?

I’ve got food and shelter pretty well taken care of. That leaves opportunity for other things. Fatherhood, relationships, career, hobbies. Finding meaning in the time that I have before it all blinks away.

If you don’t stay occupied, the existential dread starts kicking in. TV works, I guess.

But there’s something about not knowing that eats at me. That I’ll live and die not knowing most things. There’s no winning, no “enough.”

Lots of people collect. Birds, stamps, cars, mountains.

Other people build. Cabinets, birdhouses, quilts.

I do both.

The more I collect, the more sense I can make out of it. The more I build, the more I can leave behind.

I can’t help but collect knowledge. Lately, the learning feels useless unless it finds a way back out. The little connections that feel like fire in my mind get lost if they stay inside.

They’ll die with me if I don’t externalize them.

I gave my wife a bumper sticker that said “Eat well, exercise, die anyway.”

Collect knowledge, create artifacts, die anyway.

Is it just vanity? Maybe a little. I’d do this without an audience. I’m pretty sure of that.

I don’t tie flies for other people, and I didn’t spend 300 hours building a model HMS Beagle for anyone else, either. I aquascape and keep dozens of houseplants because I like thinking about those things. I like what I think about when I’m doing them.

But why an observatory? A behemoth in the front yard—not a house on a lake.

Still hard to say. I built it bigger than it needs to be. Big enough for a crowd. A place where people come and say, “Whoa.” A place where I say, “Whoa,” right beside them.

The night sky is there. It’s always there. It changes, but not in the way humans usually think of change. It’s big, but not in the way we usually think of big.

The stars are as real as the keyboard I’m typing on, but as different as anything I can fathom. They both follow the same rules. The grand and the mundane, squished together and constantly begging for my attention.

A backdrop for thought.

Everything we think takes place among the stars.

I can dive deep into my data and come back with stories.

Watch a sunset alone. Wow.

Watch a sunset with someone else. Even better.

Maybe that’s reason enough.

What I’m Reading: Wonderful Life by Stephen Jay Gould

Tortoise beats hare. Everybody knows that.

An army of monkeys eventually produces Shakespeare. Also easy.

Evolution eventually produces complexity.

Records screech, eyelids quiver.

You can’t SAY that.

Evolution is blind. No plan. No foresight. But blind isn’t stupid.

Consider the evidence:

It took two billion years to get mitochondria—to distribute enough energy throughout the cell to power complexity. One organism swallowed and then incompletely digested another. Now they’re roommates and we’ve walked on the moon.

What took so long?

Many say it was an impossibly rare event. Like getting struck by lightning while getting eaten by a shark and scratching a $10 million lotto ticket.

Wham.

Could be why it took so long. Could be why it never happened again.

Or not.

It may be that mitochondria aren’t the only possible solution. Just that they were the first.

First place populates the Earth. No room for second place.

Still, it was a long wait. But there was a lot going on.

Things had to happen first.

A planet covered with Legos and nothing but time and sunlight.

Energy storage and release. Information storage and recall. Pumps, proteins, division, gradients.

You get it.

By the time endosymbiosis happened, life wasn’t starting from scratch. It had already spent two billion years inventing things.

Evolution didn’t keep dumping the bucket onto the floor and starting over. Every useful little stack stayed in the pile.

Life didn’t spend all that time trying to build mitochondria. It spent it trying to build everything.

It’s still trying.

Making little Lego sculptures, seeing what fits.

Add another brick. Swap red for green. Turn 90 degrees. Countless molecular tricks, found one at a time.

Saved for later.

Evolution isn’t a monkey at a typewriter.

It’s more like a search algorithm with memory.

Each generation starts with yesterday’s answers.

Solving the here and now, oblivious to tomorrow. Just searching.

Genes move sideways. DNA goes rogue. Organisms steal useful machinery from one another. Life constantly recycles its own inventions.

Then one day, one kid put an entire Lego dollhouse inside a bigger Lego house.

Gulp.

Mitochondria.

We have liftoff.

Far easier than making a dollhouse from scratch.

How often can that happen?

Some exobiologists think infrequently enough that it may explain why we’re apparently alone. Some think maybe complexity is the hangup (I don’t). A universe of single-celled goo.

Two billion years is a long time. Evolution remembers.

Useful mutations stick around.

Every solution becomes raw material for the next one.

No blueprint. No goal. No diagram from Denmark.

Just accidents that happened to work, piled atop accidents that happened to work before them.

A Lego metropolis, built on trial and error.

Maybe two billion years is evidence that complexity is unlikely.

Or maybe the computation wasn’t finished.

It still isn’t.

What I’m reading: Wonderful Life by Stephen Jay Gould

He was a slight man with an unfortunate mustache and the patchy stubble of a rebellious fourteen year old. Curious blue eyes pierced through ponderous, academic brows. An unkempt coif of salt and pepper nodded toward early 20th Century Austria. The ghost of Einstein, folded into a 1998 Geo Metro.

The Professor was a silly man wearing a serious man’s career. You could glimpse the energetic curiosity of a young border collie peeking from behind the face of a grizzled old schnauzer. It sometimes seemed he had trouble sorting the two—serious out of a sense of duty, playful out of instinct. The Ghost of Christmas Past, at once young, old, playful, philosophical.

A Dickensian shapeshifter, tenured and seeking.

Some called him fanciful. Others, distracted. A serious talk about missed deadlines could become a meditation on consciousness. A meditation on consciousness might become a masterclass on salamanders.

Post-docs would jingle their keys to get him talking about information theory instead of holiday schedules.

The Professor was known to meander through his and other labs in his year-round Hawaiian shirt and flip flops, leaning over the shoulders of post-docs and whispering “publish.”

Not shirts. Shirt. Acquired on his only true vacation: Honolulu, 1994.

Its white background yellowed with late nights and coffee stains. But the little blue orchids still matched those sparkling, inquisitive eyes.

“It’s the only way people notice me,” he sighed one Christmas as he stared deep into a warming flask of growth medium.

A passing comment about snail copulation from Dr. Mellow down the hall once led to a five-year odyssey through Borneo, two divorces, and an unfortunate incident involving US customs officials and a cooler full of mollusks. The Times ran, “Snail-Smuggling Scientist Apprehended at LaGuardia.” It’s framed, somewhere.

What started as an honest question about snail sex eventually led to twenty-eight papers, a fascinating poster at a conference, and zero financial upside.

“Journals don’t pay, but I really changed the way people think about penis fencing. Also, my car keeps making this grinding noise and smells like burning… can I get a ride later?”

Many attribute his limp and the faint maple syrup odor that follows him to that mysterious stint in Borneo.

I first found him in his office, tucked in the far end of the biology building, across from the vending machines and down the hall from comparative parasitology. The place where he stores his thoughts. The extra ones. An ode to pre-digital working memory.

The space was a monument to intellectual exploration. Every surface overflowed with books, manuscripts, fossil specimens, grant proposals, and unopened utility bills. Books became stacks. Stacks became piles. Piles became furniture. A mind, manifest as a room.

Trinkets. Clippings. A series of bronzed cuttlefish. Hard-won trophies from the early, pioneering work that led him here.

He welcomed me in and beckoned me to sit in the elementary school style chairs in front of him.

The good professor sank into his favorite thinking chair. A deeply patinated swivel, upholstered as much with duct tape as fabric. A testament to timeless inquiry, deep thought, and respect for the past.

“So, what interests you about beetle sex?”

A new odor wafted my way.

The Professor had shit himself.

“Diapers. I’ve learned to prioritize.”

Elon Musk is poor. Or rich. Or something. Big numbers are weird and I can’t picture them.

Let’s play with trillions.

$1.3 trillion, as of writing. That’s a big number, usually. Or it’s small.

I want to do division.

The Earth is 1.6 trillion days old, give or take.

Musk could amass his fortune making $0.03 an hour since the Earth was a ball of molten rock.

Cooling, heating, ice ages, plate tectonics, the first single celled life, the eons upon eons of time that Earth has been Earth. Three cents an hour.

The first minimum wage was $0.25/hr.

1.3 trillion isn’t that much when you think about it.

A milliliter of water contains 3.34 × 10²² molecules.

That’s 26 billion Musk fortunes in a tiny bit of water.

Lame. The man is a pauper.

What if we convert it all to potential energy?

What could he blow up? Like, physically?

Well, he could probably invest in the R&D to make his own nukes and blah blah blah.

But let’s say all he can buy is TNT.

Industrial TNT costs about $10/kg on the industrial market (probably shouldn’t have googled that).

So he could buy 130 billion kg of TNT.

Do we even make that much?

Nope.

Planet Earth produces about 2 billion kg of TNT per year.

He’d need roughly 65 years of global TNT production all for himself.

Fire it up anyway.

A little less than one Krakatoa. The dinosaurs survive, but Napoleon fails in Asia.

I still don’t know what a trillion is.

I can feel ten, four, and seven. They have vibes. I’m made to count berries, not molecules.

I can even count trillions. One trillion, two trillion, three trillion.

But I can’t feel a trillion. It’s gibberish. It has to be like something. I have to divide, compare, wonder.

We choose the comparison, we choose the message.

I’m 1.8 trillion picometers tall. Stand back.

Most times of the year he could lay dollar bills end on end and reach Mars.

That’s a lot of Scotch tape.

Is he rich? I don’t know.

There are more cells in his body than dollars in his worth.

But there’s a number on a screen that says he’s rich.

I can touch my phone and make a coffee maker appear at my house. He can summon a fleet of mega yachts.

A trillion is a word for twelve zeroes. What a stupid number.

Thanks to for inspiring this essay during our recent podcast.

You’re lazy. Your body isn’t

It works it’s ass off day in and day out so you can while away your precious time on Earth scrolling through nonsense about kittens or whatever.

Here’s something mundane:

You absentmindedly scratch an itch a little too hard on the back of your neck while playing Candy Crush.

A tiny nick in your skin.

The first cells to die spill their guts. DNA, proteins, little alarm bells manufactured long ago for exactly this moment get dumped into the surrounding tissue.

Nearby cells hear the call.

Tiny landmines—mast cells—explode and release their contents, too. Histamine pours out. Blood vessels leak, fluid floods the area, and the itch and pain sensors get tickled.

Hey brain, over here. You’re getting damaged and are far too mortal to casually allow that sort of thing.

Whoops. Too much. Am I bleeding?

The insides of nearby blood vessels turn into Velcro and snag white blood cells.

Neutrophils arrive first. They indiscriminately explode their toxic contents at anything that looks at them funny.

Lots of damage. Lots of collateral. We call the leftovers pus.

Then come the macrophages. Little amoeba-things that crawl through the wreckage and gobble up debris.

The cleanup starts while the battle rages.

Meanwhile, detectives sift through the scene, looking for invaders and collecting evidence.

They chop what they find into tiny bits and carry it to the lymph nodes, where the immune system waits.

Found this. Have we seen it before?

If yes, your body pulls a premade immune response off the shelf and replicates it a few million times.

If no, you’re going to have to wait a week or two while it engineers an army from scratch, perfectly designed to fight off whatever nonsense was on your fingernails this time.

While you wait, the neutrophils and macrophages are going to do their damnedest.

Off goes your body’s version of personalized medicine, careening through your bloodstream and back to that absent-minded scratch.

More Velcro.

More fighting.

Meanwhile, you’re also fighting a cold, dealing with that weird pimple on your nose, pretending the hangnail isn’t there, and fighting off whatever was in that gas station sushi.

There are all sorts of troops. They attack bacteria, viruses, fungi, parasites, random molecules from outside—you name it.

Mechanism on mechanism.

Eat them.

Oxidize them.

Plaster them with antibody.

But there’s still the matter of that hole in your skin.

Platelets clot. Fibroblasts make collagen. Blood vessels form. Skin cells literally crawl across the surface to fill the gap.

Scaffolds.

Energy conduits.

Highways.

A city under construction in the middle of a war zone.

And every step can fail.

The alarm can be too loud, or fail altogether. The soldiers can attack the wrong target, get confused, or get tired. The cleanup crew can get stuck in the on position. The rebuilding process can overshoot or stall.

Job security for me.

A cut is mundane.

Everything after that isn’t.

An immensely complex biochemical algorithm.

No mind.

No thoughts.

No five star general directing the operation.

No central command.

Just inputs and outputs.

Distributed, synchronized, efficient.

All of this, running 24/7 for decades while you crush candy.

Kid asks a question:

Which species is winning?

Humans, of course.

Wait, ants? Cockroaches?

No.

Bacteria.

That’s not quite right either.

Depends on how you measure it, I guess.

We’ve spent thousands of years putting ourselves at the top of imaginary ladders. From Aristotle to listicles, we’re obsessed with ranking the natural world.

The world feels safer when it’s in boxes. Better still if we know which box goes on top.

So let’s give it a whirl.

I like ranking things. So do you.

If we’re talking opposable thumbs, calculus, and turning ancient plankton into plastic, then definitely humans.

Go, anthropocentrism.

But there are lots of metrics.

Distribution, biomass, population. Others, I’m sure (sharpest fangs?).

Humans might actually win the distribution game. Yes, there are bacteria just about everywhere, but not the same bacteria.

For biomass, things get complicated. Animals are out. Humans are barely a blip. Most of the living world is made out of plants and various forms of goo.

Maybe aspens. Maybe seaweed. Possibly algae. Humans have more important research to fund.

Let’s do population because the factoid sparked this essay.

Prochlorococcus marinus is a tiny photosynthetic cyanobacterium found throughout the sunlit ocean.

You’ve heard there are more stars in the observable universe than there are grains of sand on Earth.

Well, for every star there are somewhere around one hundred thousand P. marinus.

A gazillion little lives, all unfolding in unison.

We did it! P. marinus is winning.

A tiny green cell making more of itself from sunlight and seawater.

Is that winning?

I don’t know.

What is winning?

Humans spend a lot of time measuring, ranking, and building hierarchies. We like scoreboards. We like winners.

It helps us organize the world. Organized worlds can be conquered. We’re this close.

But evolution never made a scoreboard. It never even asked the question. Humans did.

There is no grand championship of life.

No trophy for intelligence. No medal for complexity. No prize for colonizing land.

Everywhere you look, life. For 3.5 billion years: reproduce, survive, reproduce.

We assign words to organisms. Turtle. Bird. Sunflower.

To create order, to study.

We draw boxes around a world that refuses to stay inside them.

It’s what we do.

Birds make nests.

Humans organize.

A kid asks which species is winning, and adults have spent millennia trying to answer.

One cell became two, became four. Became forests. Became whales. Became people.

We may be the only branch that stopped to ask who was winning.

Us, of course.

24 hours after arriving at the Grand Canyon from San Francisco, I found myself staring at a wall of Chapstick in a local gas station. $15 a tube. Supply and demand.

A quick flight from fog-ensconced sea level to mile-high dryness found my skin shocked and appalled by the abrupt shift to desert life. Ka-ching.

72 hours later, all better. My body figured it out. I was inconvenienced but not dead.

That’s odd.

Let’s run an experiment.

Throw a tree frog in the desert and watch it die. Throw a horned lizard in the desert and watch it thrive.

Obvious enough.

Now, throw the frog in a swamp and watch it thrive. Throw the lizard in a swamp and it might actually be okay for a while.

Also odd.

Frogs clearly need moisture, but lizards don’t seem to need dryness.

Now let’s try plants.

A potted fiddlehead fern and a cactus. Same result.

Huh.

The dependence only seems to run one way. Swamp things often can’t survive the desert, but desert things can frequently survive the swamp.

Why?

It’s hard to be watertight when you’re mostly made of water. Poke a hole in someone and see what happens.

The fact that I could visit Arizona at all is impressive by evolutionary standards.

A bag of sea water standing in a blast furnace at 0% relative humidity, marveling at ancient sea beds a mile above the ocean.

That’s hard. My lips cracked, but I didn’t need to keep dipping myself in specially conditioned water every few minutes.

The problem isn’t that deserts are harsh. It’s that they reveal dependency.

Stick a body in the Sahara and learn what it really needs.

There’s no reason to become watertight if the world already keeps you wet. That takes millions of years and niches. A tree frog in the desert doesn’t have that kind of time.

Many organisms touched land. None have fully escaped water.

But solve the desert and just about everywhere becomes accessible. You can even return to the sea.

At the Grand Canyon, my body expected humidity. It got caught with its pants down because people invented airplanes.

Arizona would kill us astonishingly quickly without a keratinized epidermis.

A little Chapstick and a Nalgene go a long way.

But that Nalgene tells us something: we haven’t fully escaped the sea.

We lose water with every breath we exhale. Every bathroom break, a literal leak. Sweat enough and things start looking dire.

Human skin and kidneys work overtime to keep our fragile innards suspended in a tiny private ocean while we explore where air touches rock.

Our own personal spacesuits that allow us access to places fish and frogs only dream of.

Put a person in an actual spacesuit and push them through the hatch.

The Sahara turned up to 11.

What do humans really need?

A $30 million barrier between us and the vacuum of space. Inside that, an atmosphere. Inside that, skin.

Inside that, a drop of ocean.

Your skin is much bigger than you think, and most of it is hidden. It has to be.

Also, you’ve got a tube that runs clean through your body. Odd.

You put things in the tube. Stuff comes out the other side. It never feels like part of you.

Cheeseburger in, poop out.

At no point would someone look at what’s in the tube and say, “Yup, that’s me.”

So what gives?

Watch a bacterium eat. Food crosses the membrane and powers the cell.

The membrane does other things, too. Protection, gas exchange, ion management, waste removal, reproduction, you name it. The lining does work. Every organ wrapped into one surface.

But we’re multicellular. Opportunity.

And we’re huge. Challenge.

Volume outstrips surface area as objects grow. Big organisms need big innovation.

Let’s trace your skin.

Start on the middle of your forehead and run straight down your nose, over the philtrum, around the lip and into the mouth.

Hard palate, soft palate, around the corner and up into the sinuses. Mucus and immunity.

Bounce around for a minute and get turned down the back of the throat. Down the esophagus.

Through a door and into the stomach.

This skin leaks acid.

Through another door and then 30 feet of intestine. Thousands of fingerlike projections compound surface area. Flatten it out and reveal just how much is dedicated to breakdown and absorption. Too wet for outside: too delicate.

Another door. Colon.

Then, out the other end.

Back in. Through the reproductive tract, past the ovaries and testes.

Into the bladder. Up the ureter and into the kidney. A delicate filter where your blood touches the outside world.

Back out. Up, over the chin, into the mouth again. Now, the airway.

This is where blood touches air. Dead end in the alveoli—impossibly delicate, gossamer-thin bubbles. Again dedicated to surface area. Again, much safer inside than outside.

Home stretch, back to the forehead. We’ve been everywhere.

One folded surface.

Stretch out what we traced and it sprawls across the floor. A living room rug’s worth of interface for a single person.

Most of it processes nutrition. A little for reproduction and waste management, a whole lot for gas exchange. Some for defense and sensation.

Almost all of it is built on surface area. Only a little is skin as we know it. This is multicellularity’s answer to the cell membrane.

It’s because we’re big. We need more surface to support our massive volume.

Cells stay small because surface area matters. We can be big because we’ve origami’d our skin into ourselves.

Most of our outsides are hidden on the inside, where we chemically dismantle the world by touch.

You find yourself in a space station, marveling at your own weightlessness and trying to figure out which way is up. You peer out the window and wonder at the cosmos--- David Bowie eat your heart out. The air is cold. Windy. Fans blow in your face. The room is bigger than you expect. You sense a presence.

Odd.

AAAAIIIIIEEEEEEEE!!!!!

Holy shit, there’s a dolphin next to you. A beach ball bonks off your head.

It stares at you quizzically and nods its head rapidly before unleashing a barrage of clicks and squeals. It’s... happy. Not a drop of water to be seen. You notice a flip calendar: “Mission day 100.”

The dolphin gestures to a square of sandpaper Velcroed to the wall and a little sign that reads “Dolphin Polishing Station.” Next to it, a jar of Vaseline. Then, a bag of mackerel.

You lock eyes with the beast.

Oh no.

You wake up, stare at the ceiling for a moment, and realize the dream was annoyingly plausible.

How?

I’m pretty sure it’s possible with a big enough budget and motivation to match. Not easy. Not comfortable. But plausible.

When a whale beaches itself, it’s the gravity and heat that get them, not the dryness. Muscles crush, nerves compress, and blubber traps heat.

Because whales are land animals. They don’t need water the way fish do; they just evolved to depend on it mechanically.

Their bodies—bones, nerves, muscles—expect support from water. If your family hadn’t felt gravity for 50 million years, you may expect it, too.

But whales were land lubbers for 300 million years, and their innards still carry that history. We share ancestors who became water-tight. “Fish” is a successful shape, but evolution doesn’t hit rewind. It modifies.

Mammal organs are fish organs adapted for land. Whale organs are land organs adapted for water.

They don’t go back to being fish organs. That would be weird.

Land animals seal out the outside world, because the outside world is dry and hostile.

Whales, people, mice. All bags of seawater: exquisitely managed on the inside, sealed on the outside by a keratin-based epidermis.

Instead of becoming more permeable like a fish, whale skin doubled down on what it was already good at. It’s hermetically sealed. Sweating would be a terrible strategy for a mammal living in saltwater. Whales still run modified mammalian plumbing. They conserve water aggressively and get most of it from food, not from casually drinking the ocean.

So what does it mean?

Well, it means you could probably keep a whale happy out of the water as long as you don’t make it feel the weight of its own body and keep it from overheating. Among a couple other things. You need to help it know which way is up, keep it exercised, and keep it entertained. Scott Kelly probably has thoughts on this.

But about the sandpaper and the Vaseline.

Flipper’s skin would likely need the most work in space. It’s become highly specialized after millions of years in water. The fact that it’s sealed is good for business, but there’s a problem: epidermal turnover.

We constantly make new copies of our skin and completely recycle it every 28 days or so. Dead skin sloughs away and is replaced.

Whale skin is faster. Much faster. Ocean water strips it away about as fast as it gets made.

But on the space station, it just piles up.

Our sleek, smooth dolphin starts looking like your crusty great-uncle Bert after only a day or two.

There’s only one thing for it. You have to—ugh—polish the dolphin.

And has anyone ever tried to potty train a dolphin in zero gravity?

Suddenly, that polishing job doesn’t seem so bad.

Life is like a leaky tire.

Not philosophically. Biochemically.

Poke a hole in a tire and feel the air leak out against your hand. Hold a tiny pinwheel next to the leak. It turns!

The air in the tire is doing something. Attach some gears to the pinwheel and you could get some work done. But then the air runs out and the pinwheel stops. Huh.

Your spouse tells you to stop screwing around and fix the damn tire. Right.

But about the pinwheel.

It turned because there was more air on one side of the tire than the other.
Earlier, an air compressor created that imbalance. The energy used to compress the air wound up stored in the tire. Pop. Hiss.

A kilowatt hour, finally spent.

Energy rolls downhill and entropy increases. Cream diffuses through your coffee while the coffee gets cold. The tire goes flat. Interesting at first, but eventually boring.

Equilibrium. It’s boring, and the universe likes it that way.

But now make millions of tiny leaks with millions of tiny pinwheels, and attach an air compressor that continuously shoves the air back in.

Now you can power lots and lots of machines.

Replace the air compressor with millions of tiny ones, and you’ve made a cell.

Not just any cell.

Every cell.

Pretty much every living cell we know of runs on this exact concept. Just instead of air, it’s protons (and occasionally sodium), and instead of rubber, it’s a cell membrane.

And the thing is, the pinwheel actually is a pinwheel.

All over every cell membrane in every cell of your body are countless tiny molecular pinwheels spinning at unfathomable speeds.

We named these ubiquitous pinwheels ATP synthase, and evolution has stubbornly held onto the design for billions of years.

A channel, a wheel, and a wall. Protons whiz by, the pinwheel spins, and ATP flies out. A tiny Hoover Dam.

The ATP spewing out of the pinwheel holds a tiny packet of energy. That energy is the common currency of life. A universal penny that all of life accepts.

Elsewhere on the membrane, protons get pumped back where they came from. The energy comes from all different mechanisms across life. You can power your compressor with sunlight, chemicals, volcanic vents, food, or whatever. It’s the pumping that matters.

And the leaking.

And the membrane.

About that membrane…

None of this works without a container. An air compressor running in your driveway can’t create a gradient that does anything.

Life—Earth life, anyway—doesn’t defeat entropy. It controls the route toward it.

By making skin. The membrane isn’t metaphorical. It’s literal.

Textbooks talk about membranes as barriers. Gates. Interfaces between inside and outside.

All true.

But it’s also about the simplest way to precisely control gradients for the purpose of doing work. It lets life control the leak.

Sci-fi writers talk about sentient gas clouds and micro magnetic fields. I’m not so sure. It all sounds like air compressors blowing against nothing.

It all starts with a leaky tire.

We spend our lives pumping against the leak, pushing against equilibrium while the universe patiently waits.

Eventually, the tire goes flat.

My immune system has decided that Lodgepole Pine semen is an existential threat.

Every year at about this time, our forest reminds me that it’s full of perverts. Trees and grasses alike flip on the Barry White and engage in a group sex act so profoundly gargantuan that it can be seen on weather radar.

Their Bacchic mess winds up everywhere. For about a month every spring, a film of plant sperm covers our corner of Montana, sending my body into a tailspin of histaminic rage.

Time to know thine enemy. Pollen.

It’s everywhere because it has to be everywhere. Plants can’t walk.

It’s a big engineering challenge: project your biological presence into the environment because you’re literally rooted to the ground. That’s hard. The air is a hostile place.

It’s not a new problem. It’s as old as reproduction itself. Two organisms need to swap DNA and make a new organism.

Animals and other motile critters have it easy. They mostly put their cells into each other. Simple enough.

Other organisms let the environment do the work. Release your reproductive cells and let them swim to or just drift into each other.

Fish and algae do it all the time. Broadcast spawning.

Plants do it, too. Liverworts send their sperm swimming through the water. But that tethers them to the water.

Introduce air as the broadcast medium and you’ve got much bigger problems.

After all, we and every cell in every living thing are essentially bags of seawater. The more extreme the environment, the more extraordinary the hoops.

You have to launch living cells into the atmosphere. Across a dry, oxidizing, UV ravaged sky. It has to survive and land in exactly the right place, despite having no control over where it goes.

So you have to make a lot of them, cheaply, and hope for the best. Floating cells. Disposable cells.

It isn’t dust. It’s alive.

Tiny packets of ocean chemistry, nearly indestructible and so numerous that they blanket continents and ruin springtimes for dermatologists.

Inside are living cells. Usually two. One becomes sperm. The other grows a tube. When pollen lands in the right place, the tube grows toward the egg. An aqueous channel, finally. The sperm does what sperm does, and voila.

Weird at the beginning, familiar at the end.

But for all the constraints, wind pollination has evolved over and over again. Pines, grasses, sedges, oaks.

All of them learned the trick, because they had access to the same ancient capsule material. Sporopollenin.

And it evolved long before plants conquered land, back when spores drifted and plant sperm still swam freely in open water.

One of the most chemically stable and poorly understood materials in biology, built into the shared history of everything that makes seeds.

So came pollen. An aquatic reproductive system, floating in the sky. A different kind of ocean, the same kind of solution.

There was no need to invent a better molecule, just a better package.

And so, Montana disappears beneath a haze of sex dust. The forest launches trillions of microscopic, armored gametophytes into the atmosphere and lets probability do the work.

My immune system calls this a crisis.

Evolution calls it one of the greatest engineering solutions life ever discovered.

Just don’t get me started on plants that trick insects into rolling around in their genitals. Yet.

Note: I’ve been reading When the Earth Was Green by Riley Black and it’s really got me thinking about plants. You should check it out.

I bit into a jalapeño popper the other night and realized: this plant is trying to tell me something.

It didn’t want me to eat it. But fruit is supposed to be eaten. That meant something else was supposed to. Something that can’t taste capsaicin. A discovery, waiting to happen.

Darwin once predicted the existence of a moth with an incredibly long proboscis because he found a thin, slender flower that demanded it.

The main and probably only difference between me and Charles Darwin is that I have a cell phone.

Birds. Birds can’t taste capsaicin.

Birds often swallow pepper seeds whole, but mammals usually grind them up.

The whole point of fruit is to put seeds in fertilizer.

Mammalian molars are very good at destroying seeds, which simply won’t do if you’re a pepper plant just trying to have babies.

Birds are more of a down-in-one situation. Seeds go in. Oftentimes, seeds come out.

Darwin got famous, and I predicted that birds don’t chew. Another beer, please.

Actually, they do chew. Just not in their mouths.

And not with teeth.

They swallow rocks and use them as grinders. Poorly.

What is even happening? I’ve known forever that chickens swallow rocks, but never spent time unpacking this with an evolutionary lens.

Plants tell you which parts to eat. Fruit is delicious. Leaves are fibrous and usually bitter. Seeds have shells and husks.

If you want to get nutrition from leaves and seeds, you have to break them.

Mammals and dinosaurs cracked this nut in very different ways.

Mammals carry grinders in their heads, and that comes with advantages. Chewing allows the mind to ensure that as much nutrition as possible gets extracted from each bite.

It’s efficient, but when you’re eating, that’s all you’re really doing. And if you’re trying to survive on plants, you’re eating all the time.

Many dinosaurs chose volume. Most teeth tore and chomped, but didn’t grind. Bird ancestors were carnivores built for tearing flesh, not grinding plants. Enormous amounts of food went in, and the stomach was left to do the work.

Enter rocks: the teeth of the stomach.

Dinosaurs with gizzards could eat quickly, then move while digestion caught up.

Which has been helpful for birds. They swallow everything whole and then fly off.

No need for front-heavy chewing muscles. Compatible with a fly-at-any-moment lifestyle.

But a muscular sack and a handful of pebbles don’t grind seeds with the same efficiency as teeth.

Some seeds get through. That’s what matters to a pepper plant.

The heat on a jalapeño popper isn’t a warning. It’s a filter.

The plant wants its fruit to be eaten—just not by you.

We’re all just worms with fancy bits stapled on.

If you internalize that fact early enough in life, you start noticing things. For one, it’s weird that we show affection by touching mouth parts.

Strip away the legs and hair and you’re basically left with a tube. Food goes in one end, waste out the back. Genitals somewhere in the mix.

Despite all their art, politics, and obsession with TikTok, many humans spend a lot of time securing calories and safety so they can live long enough to create and rear young. Birds and ants seem to be interested in the same things.

It wasn’t always like this.

Let’s build a worm.

First, rewind a few billion years.

For most of life’s history, there was no front or back.

Early life floated, or stuck to things. A tiny world where things like impact, friction, and falling had little meaning.

Life cared less about Newton and more about perfecting the pathways that keep us 47% genetically similar to fruit flies.

Microbes dealt with chemical problems. Drop a little too much fresh water in a briny pool and whole colonies exploded. No time to worry what might happen if a rock falls on you.

But life, sunlight, and time have a history of building complexity. As long as you leave them alone long enough.

So let’s come back in a few billion years, when things start looking more wormy.

600 million years ago.

Nerves—life’s information superhighways—started firing by the early Ediacaran, when jellyfish drifted through the seas.

Action potentials transmit information over large distances to many cells at once. Nerves gave animals a command center that could send high-fidelity messages over distance.

Life began running on two scales: DNA controlled the tiny whirs and zips inside cells. Neurons steered the ship, and let the ship get really big.

Modern nerve signals move at ~100 m/s; fast enough for a sauropod to flinch when you step on its tail. Diffusion would take years to decades to do the same job.

Jellyfish Earth probably looked a lot like pre-jellyfish Earth. Except there were jellyfish, and some really interesting UFO-like organisms that descended on microbial mats.

But no vectors. No macroscopic over there.

Then it happened, sometime in the late Ediacaran. Something in the mud—something that knew up from down—moved forward. Toward something. No guessing, no filtering.

That way.

A worm. A tube with a front, back, left, and right. Undulation be damned. Worms could seek. They could follow.

Successfully. Explosively, even.

Worms learned to graze, scavenge, and hunt. They could flee. Maybe even love.

Worms awoke from whirring metabolic machinery and discovered the world we take for granted. The one where we feel water currents, experience gravity, and can duck a punch.

Worms discovered time as we know it.

Catch a ball. Worms did that.

They discovered an empty playing field that had been there all along, hidden by perception. Everywhere around them, other life was stuck in the old way of being. Slow from far away, blindingly fast up close. Totally non-threatening on the scale of meters. Everything became food.

So, evolution did what it always does in a vacuum: It radiated.

Life rushed to fill the world with possibility. Evolution flung spaghetti at the wall. Most of it didn’t stick, but some did.

Teeth, pincers, claws, bones, arms, legs, shells. Organs of all shapes and sizes.

Eyes and skin coevolved into an endless menagerie of colors and patterns.

Worms, all.

Humans have thumbs and language and spaceships and war. We move with intent. Our watches tick seconds because rocks take seconds to fall.

We live in a world discovered by worms. A world with direction, and time.

It didn’t have to be this way.

We don’t come from them. We are them.

***Thanks to for encouraging me to illuminate this manuscript.

Plants invented fire.
On Earth, anyway.

Stay right where you are, but rewind 2 billion years.

You’re wearing a fully contained hazmat suit complete with SCUBA-style oxygen tank. Without it, you’d suffocate in a CO₂ and methane-rich atmosphere before you had time to run this thought experiment.

It’s nighttime and your flashlight just went out. You need to see your watch or something bad will happen. Your visor is fogging and time is running out.

Thankfully, there are matches in your pocket. You nervously strike one. The phosphorus fizzles for a second or two, and then goes out.

You try again. And again.

No fire. Just a faint smolder and then nothing. It doesn’t matter what you feed it. Nothing catches.

Plants haven’t invented fire yet.

Fire needs oxygen, but this Earth has almost none.

How could this be?

Pop sci writers love to remind us that you can’t unmix your cream from your coffee.

Globally, true.

Locally, plants separated the coffee from the cream.

In early Earth, all the carbon and oxygen were stuck together as CO₂. Plants figured out how to yank them apart and store the energy needed to do the yanking.

Carbon in the plant, oxygen in the atmosphere.

There’s sunlight in the plant. Heat up a plant near oxygen and the sunlight comes back out. Fire. CO₂. Entropy.

Fire mixes the cream back in.

But if everything mixes back together, the system resets.

Photosynthesis churned for a billion years before fire could burn. Cyanobacteria died and their carbon was released. Oxygen climbed high enough to cause multiple mass extinctions, but your match would still fizzle.

Something else was needed to tip the balance.

Plants.

Plants are big, made of carbon, and get buried in the mud.

Separate carbon from oxygen, then hide the carbon. You’re left with a surplus of oxygen, ready to ignite the world. Give the atmosphere fuel, and something—fire, bacteria, you—will turn it back into CO₂.

Wait, this is all just a battery, isn’t it?

Early Earth had the ingredients for today, but they were in all the wrong places and mixed up.

It was creamy coffee.
A dead battery.

Life and sunlight created voltage.

Voltage on a global scale. Work done against entropy. We search for it when we point our spectrographs at exoplanets.

When we look for life out there, we’re looking for other batteries.

But for now, we don’t know of other batteries like ours. Earth is the only place we know of where you can find something on the ground and light it on fire.

Everywhere you look, Earth burns.

Breathe in oxygen. Breathe out CO₂.

You are the fire.

Most cave people weren’t cave people at all. We just think they were because things that go into caves tend to stay there.

Look at an image of Earth at night and you’ll notice it: a glittering string of lights along the coasts. People like the ocean. Calories, transportation, views. What’s not to like?

This isn’t a new idea.

Early humans likely thought the same way. During the Pleistocene Ice Age, they moved from Asia into the Americas, probably along the coast.

Kelp, fish, seals. A long walk on the beach.

We think that’s how it happened because inland routes were covered in ice when the first human sites appeared in North America around 14,000 years ago.

So they likely followed the only open path. But it was the Ice Age, and those ancient coastlines are now tens to hundreds of feet underwater. We can’t easily access them. We can’t walk those routes or search them for archaeological evidence.

But we have a rough idea of what they were like. We’ve mapped the seafloor off the West Coast, and that part of Pleistocene North America was a vast lowland plain.

Smoke from a driftwood cooking fire hung over grassy, windswept marshland as early humans swatted flies and gutted fish. Charismatic megafauna wandered those plains. Mammoths, saber-toothed cats, and all manner of other giant mammals roamed the edge of the continental shelf as our ancestors followed them onto a new continent.

Then the ice melted.

And those plains became kelp forests.

That early, most consequential human world was drowned under rising sea levels. What did they wear? Eat?

Did they draw? Carve? Make jewelry? We can’t know.

Only fragments of our early coastal history remain: a few shell middens. Reminders that people liked shellfish then as much as they do now.

But humans are resourceful storytellers.

Enter the cave people. Or, more accurately, the accidental heroes of early human cultural imagination. They certainly existed, but were probably less common—and perhaps more eccentric—people who lived in holes in the mountains instead of along the vast, food-laden coastal plains.

We know a lot about them because things preserve well in caves. They made their paintings where they wouldn’t wash away, and threw their garbage even deeper inside.

Their coastal cousins didn’t leave much behind. The tide came in on their world, and we’re left to wonder.

Or not.

We tell stories about what we can see and touch. Scientists especially.

There’s a real bias against speculating about what we can’t see but know is there. You can see it in how we imagine cave dwellers, and in the near absence of coastal humans from that story.

Those coastal people were probably numerous, different in culture from cave dwellers, and responsible for a lot of the distribution of our species across the planet. They played a central role in who we became, but get almost no airtime.

If we can’t hold it, we don’t tell the story.

Go to a fossil exhibit, and you won’t hear as much about cardiovascular systems, or slugs, or bioluminescence—the things that don’t fossilize well. You’ll hear about trees and carapaces and teeth.

We find ourselves locked into talking about what we can find, and hesitant to be wrong about the things we know are there but can’t see.

I look at the sky and think about biosignatures. Entire worlds inferred from the way their light smears through a prism. An artist’s rendering in a press release. A NASA scientist hedging about the anthropic principle.

We’re comfortable reconstructing the past from fragments we can hold.

Physical tethers conjure memory. We buy souvenirs for a reason.

But the most important parts of reality are often the least recoverable.

If we’re going to fill in the blanks in this universe, we’ll need to learn to see what we can’t hold.

Yellow isn’t a color. It’s a choice our brains make.

If you’re over 30, you know that night used to be yellow. Before full-spectrum LED street lights took over the world, we lit our cities and cul-de-sacs with sodium lamps. Electricity passed through sodium vapor, and the excited electrons emitted a flat, nearly monochromatic yellow that colored the world.

589 nm. That was it.

If you’re under 30, go look it up on your phone. You can see what that yellow looked like.

But you can’t see that light unless you stand in front of a sodium lamp.
Because what we call “color” isn’t the light itself.

Your phone can’t make that light. It can only trick your brain into seeing it.

We intuitively know this. Get really close to your TV screen and you see little red, green, and blue dots. No yellow. No orange.

So what gives?

Well, we have three types of cones: red, green, and blue. We named them for the wavelengths at which they’re most sensitive, but they have wide response curves that, taken together, cover the whole rainbow. The curves overlap.

It’s the overlap that creates our world of color. Shine some yellow light into the eye, and the red and green cones fire at the same time and you see yellow.

But here’s the thing: your brain only measures how much the red and green cones are firing. It doesn’t know how they got there.

That means you can shine a little red light and a little green light into the eye—just enough to match the response of pure yellow.

The colors don’t mix out there. They mix in your eye.

The result? You see yellow, even though no yellow light ever entered your eye.

Why bother parsing the infinite ways something can look red if you’re really just trying to tell if you’re bleeding?

So the brain measures the activity of red, green, and blue, then presents us with a color. Three channels. Three values. All other information gets lost on the way to your mind, even though it’s still out there in the world.

But that compression starts to break your intuition once you see it.

Humans figured out the red, green, blue trick a long time ago, and in fact developed the CIE 1931 color space by asking test subjects to reproduce colors with red, green, and blue light sources. Model those three values, and you can build a screen that produces millions of colors.

Our screens don’t reproduce light. They reproduce sensation.

Sometimes, that compression isn’t enough. We need to know more than our brains can tell us.

How do we know what Neptune’s atmosphere is made out of? You can’t tell just by looking at it. It’s blue. So what?

Well, it’s not just blue. It’s blue after you add up all the light scattered and emitted by the gases in its atmosphere. Just like sodium emitting 589 nm, we can run Neptune’s light through a spectrograph and split that blue back out to figure out what it’s made of. All that information is baked into the blue of Neptune, but our brains aren’t built to read it.

Our brains aren’t built for hard edges, either.

Run sunlight through a prism and out pops a rainbow. ROYGBIV.

It’s a line, not a circle.

But our brains don’t like that red doesn’t touch blue.

So what do we see when we excite just the red and blue cones, on opposite ends of that line?

Magenta.

A color our brains invent to close the loop—to turn the spectrum into a circle instead of a line.

Only possible when red and blue light enter the eye at the same time.

In other words: there is no magenta light. It’s not on the rainbow. It doesn’t exist as a wavelength.

Magenta is an idea, not a property of the world.

Which is humbling, if you ask me.

We take for granted that color is a property of reality. But we take shortcuts, invent sensations, and lose most of what’s actually there.

And still, a sunset overwhelms.