Cursed current! It flung me in the path of a jet of hot water exiting an underwater vent. The proteins on the hot-facing side of my cell wall denatured and cracked, and my lipid cell wall loosened for a fraction of a second.
I started to erupt my insides out, but something bumped into me – plugged the flow – and my membrane snapped back around the contaminant. I went sploing, and felt very, very odd. The edges of my more rigid cell wall fluttered in the turbulence, kept in place by proteins stitching wall to membrane, as I oriented myself.
I rode an eddy into a column of cooler water. It was still in me. No – not it – he. This was definitely a living, stormy little personality inside my membrane, agitated by the warmth of my cytoplasm and the density of organic compounds right outside his cell wall. He tried to push out his metabolic waste products out into me, even as mine trickled into him. “What is this? This place is death!” cried out the bacterium.
“Why did you careen into me?” I said, belligerent with my own fear and confusion. “I was minding my own business.”
“You rushed me. I couldn’t do anything about it – you’re three times bigger than I am,” he snapped. “It was like being hit by a silicate grain. Which would have been fine, because a silicate chip wouldn’t engulf me.”
“Engulf you! As if I did it on purpose!”
We lapsed into a long, miffed silence. I became aware that he was dividing. Using material in my cytoplasm!
I could do nothing about it. I couldn’t have torn open my membrane again to eject him even if I wanted to. I drifted, mending, pumping out the waste products of that mending.
It had been a long time since he and I had anything in common. We had diverged over a billion years, when the seas were hotter and more acidic. Some especially distant archaea were other to me, but bacteria were deep other. Occasionally I had extended a bridge to exchange genes with such deep others when it seemed advantageous, but I’d never before seen so intimately and extendedly how different a bacterium was from me. His cell membrane used right-handed glycerol and was held together with ester bonds, where mine used left-handed glycerol and used ether bonds. He thrummed with alien biochemistry. One of his fundamental energy converting proteins was turned the wrong way on his membrane. Repelled, I decided not to linger on it.
But soon his differences encroached upon mine in the most violent and personal way possible. After he divided, one of the copies died. When the dead one’s membrane broke, his genome came spilling out and smashed into mine.
Having his DNA mix in with mine was bad enough, but we both carried a small number of genetic parasites – genes just active enough to insert themselves into our genomes, and splice their RNA transcripts out before they were read into proteins. Mine were reasonably adapted to me, and knew how where to insert themselves to not wreak havoc.
But his didn’t. They cut themselves into my genome randomly, and failed to seal it up back into a ring when they were done, breaking up my genes into straight, uneven pieces.
“Bfuh! Gnah!” I was truly cross now. “Can you not splitting do that?”
“What, die in a hostile environment?” the remaining bacterium said sarcastically. “Because there isn’t enough food? Well, archaeon! You have my deepest apologies!”
Infuriated, I started cloistering my genome in a protective wreath of lipid bags to mitigate the next invasion of genetic garbage. Which came, again and again. I myself divided repeatedly, hoping each time to find myself in a body with no copies of him. A few of such versions of me were indeed free, and drifted away – to an unclear fate. We were by now all burdened with a cluttered genome that would would need time to pare itself down.
All of us naturally lost genes. The ones who did (and survived the loss) divided faster, because we used less energy on transcribing them into proteins. We periodically gained new genes from small trade with neighbors who seemed healthy. But given the extent of the bloat, it was unclear we’d lose the extra sequences fast enough before our burgeoning energy needs drove all of us extinct.
…although something interesting was happening: the obverse genetic sickness was being forced upon him. He was in reproductive competition against himself (in me! disgusting!). Versions of him that pared down their genome, as always, reproduced faster and outnumbered the others. Normally a creature that lost too many genes would just die, but… you see, I was making the proteins he would normally make, since his genes had gotten tangled up in mine. And being inside of me was so stable that many of the genes that adapted him for more heterogeneous environments dropped away harmlessly. He was getting… really sleek, and small, and hot – several entire Kelvins hotter than me at this point.
More and more, what he was doing was just making ATP – sucking up protons until his exotic ester-bonded membrane glowed with a potential as intense as lightning, and spitting them out through tiny protein motors embedded in his membrane to make energy.
Which I could use, too.
Which I, in fact, had to use. Not having ATP was dangerous, but having too much of it was dangerous too. I used it to make all those extra proteins coded by the DNA he was stuffing my genome with, of course. But I also got bigger. I knit the cloud of lipid bags around my genome into something sturdier, a complete seal between the inside where DNA was transcribed into RNA, and the outside where RNA was translated into proteins, so I had more time to splice out the garbage from the RNA before it was translated.
And it still wasn’t enough. He burned brighter and brighter as his needs pared down (while his energy production remained constant). I had to use it for something. Out of sheer self defense I made a cytoskeleton with all that spare energy. It let me make different shapes, on purpose, with myself.
“Huh,” he observed, seeing this. “You could engulf more stuff on purpose, if you wanted to. By… er… using yourself to pinch around them.”
“I have had enough experimentation with engulfment to suit me for four planetary lifetimes, thank you very much,” I said icily, but in the end I was too curious. I tried it. I found some small wiggling creature too ignorant of my new capabilities to know she should flee, and wrapped myself around her until her insides came spilling out into me for me to repurpose.
I was dazzled and a little frightened. What was that? She had just been minding her business and I had come along and destroyed her for my benefit. I had… I needed a new word for what had just happened… I had eaten someone. What had I become?
I floated, despising myself and despising him (although I admit a part of me admired him for how immediately he had seen the application of the new cell structure). I wished dearly that I’d eaten him instead, that I’d successfully punctured and destroyed him instead of harboring him –
(but if you had, you’d be lonely)
Lonely? The notion hit me like a bubble of turbulence. What was lonely? It was an inverted notion: solitude and independence, but bad, somehow. Ridiculous. He had done nothing good for my existence since he entered it, quite literally.
I could not help but notice most of us big, doubled-up creatures died. I was relieved when I met any cousin of myself. It was some sign that our existence might be viable. We were rocketing along some grotesque evolutionary path that seemed untrodden for a reason.
If I were to die there was no future for him either. And at this point I would die too if he did. Our fates were one.
“Listen,” he said, one of those times I smelled a cousin – another doubled-up creature with a colony of little no-longer-quite-bacteria – and started instinctively following her chemical trail. “I’m going to say something crazy, but hear me out.”
“Fine,” I said.
“We’re going to go extinct because our genome is too big. Even if we’re working well in some ways, we’re bound to have other things that are going wrong, just because we have so many genes.”
“Not crazy,” I said. There was no longer rancor in my agreement. I could not blame him anymore for the genomic bloat. Will all the energy to go around I’d found myself adding structures of my own, all sorts of shamefully decadent specialized vesicles that I would never have considered in my old life. And the larger I’d grown the more space there was for him to proliferate in me, filling the interstices and giving me even more energy. There were hundreds of him in me now.
“When you meet that next cousin, line up your genome with hers – your entire genome – and trade copies. If it doesn’t fit you might have to do a bit of a merge, which will be scary, but –”
“This isn’t,” I started suspiciously, and stopped.
“What?”
“This isn’t a ploy to come into contact with a new population you can trade genes with, is it?”
There was a truly hurt silence, during which ATP continued to flood out of his tiny, hot, electrically charged bodies to power my cellular processes. An involuntary reaction upon which I was now utterly dependent.
“Oh, come on,” I said. “Is it so offensive of me to ask? You’re trapped in me, you have no opportunity to meet anyone of your own kind except for clones. It’s been many years of this barely-life for you. It would only be natural.”
“I don’t need to meet anyone new,” he snapped. “I’ve accepted that this is my lot now, and I have to do novel things to survive it. Have you?”
We did not speak for a while. When I caught up with the cousin, I dawdled before brushing up against her, gripped by fear of more existential change. But I didn’t want to be a coward and I knew I’d been a cad to my little guest.
I extruded a conjugation pilus out towards the cousin, and pushed genetic material through it. Except this time I wasn’t sending just a few genes, but a full copy of my genome.
She was astonished, and a little reluctant. She almost cut the connection several times before she made up her mind: she opened a second connection and pushed through a copy of her own.
“Fair’s fair,” I said, and took it.
Like me, this cousin had a collection of straight chromosomes, a legacy from the initial damage from the genetic parasites. It took a bit of work to capture every single strand and bring it into my nucleus.
The differences between us were nontrivial; we must have diverged a while ago. Now what? Express both sets of genes, halving the ATP expenditure per gene? I supposed so. Nothing particularly dramatic happened.
When it was time to divide, I copied both genomes. My little guest spoke. “Once you’re done, divide up the genes into two piles.”
“In the original combinations?”
“No, of course not. Do it randomly.”
So I sorted the genes into two groups and an hour later I had a sister, not a clone, who took half of the mitochondrial population. We drifted together for a bit, sizing each other up. After a while it became clear she was the fitter. Even though this made me the loser, I was happy. We had made something better, rather than simply waiting and hoping.
“We must do this again,” I told her. “We must all start doing this now, carrying two copies and exchanging one of them. This way we’ll stumble faster on good ways to be arranged. Perhaps we can all survive.”
Truthfully, neither of us were optimistic. There was nothing else like us in the whole ocean. If we were the only ones in a niche, and we hadn’t been in it for long, it was natural to assume it wasn’t a good one to be in. But we drifted apart, and the practice spread, because the next time I met a cousin-creature, she knew what it was all about and proffered a whole copy first.
But some hundred thousand years later, sex was more universal among us than had once ever seemed reasonable, and we were still alive. Not just alive, but gloriously and healthily alive. I was humbled enough by the results to say, earnestly, “You were right and I was wrong. Thank you.”
My little tenant hummed in pleased acknowledgment, lighting me up. There were now thousands of him dotted throughout me. His genome was nothing but a dozen proteins. Mine, on the other hand, had tens of thousands – and that felt fine. I brimmed with more decadent vesicles than ever, all serving a justifiable function. “I forgive you,” he said simply.
I had once seen him as a parasite. Now I felt like an ungainly oafish thing feeding off him. We had proliferated beyond our wildest hopes; there had been so many of us doubled-up creatures now, for so long, that some of us could not meaningfully swap genome-halves. We were too different. This was unheard of – even bacteria and archaea, which had diverged almost at the beginning, could swap gene pieces.
“I’ve been wondering how I can ever make it up to you,” I said.
“You are home to me,” he said. “I am content with it.”
I took his word for it, but I remembered what he had done for me, and I kept thinking. A billion years later some distant bacterial cousin that had cracked using water (water!) for energy had been so long at work that the ocean could not hold more of its byproduct, oxygen. It was a potent, nasty little gas but we had over the years acclimated over and over, and not died of it. After so much not dying from it, I’d been turning around in my head the notion of using it, coming up with an idea of how it might be done. It was my turn to make a bold proposal.
“To breathe it? How do you mean?” he asked.
I showed him.
It took many years, but he was patient, and acceded to powering my experiments. Eventually I was a colony of myself, anchored to the sediment in nutrient-rich waters with calm currents. Information and fuel thrummed through connected copies of myself. Other lifeforms drifted by in the water and sometimes settled on us. Almost too tiny to register, even though some of them were thousands of times larger than my little tenant and I had been when we came together.
I was a frondthing now, towering colossally above the quartz-speckled dolomite mud of the seafloor. Large and studded with sensors all over my surface – not my cell surface but my metasurface, my skin – I could feel the ocean. Not as one vector carrying me from one place to another, but as a collection of multidimensional movement – fast or slow, cold or hot, silty or clear, turbulent or laminar, acidic or alkaline.
The billions of hot, charged sparks of him permeated my body as I extended the drifting sheets of myself to sift the water for hydrocarbons and sulfides to feast on. A meter tall; the biggest and most spectacular creature that had ever existed. Being alive, I thought contentedly, feeding him sugars and fatty acids, couldn’t get more magnificent than this.