Kael-7 was seventeen years old when they lost the ability to dream. It happened in a gene-splicing clinic in Sector Crimson, one of the thirty-eight pressurized domes that now constituted the city of London, two hundred feet beneath the surface of the Thames that had swallowed the old world sixty years ago. The clinic was called HelixPoint, and its advertisements — projected directly onto the neural interfaces of every survivor in the sector — promised upgrades that would make the human body obsolete. Kael-7 had gone there for a respiratory enhancement, a standard procedure for anyone who worked in the flooded tube stations where the air was thick with methane and the spores that grew on the walls of the old tunnels. The enhancement worked. The dreams stopped.

Kael-7 did not notice the loss at first. Dreams were a luxury in the domes, a remnant of the old human brain that evolution had not yet discarded. What mattered was survival — oxygen levels, nutrient intake, mutation stability. The neural interface implanted at birth tracked all of these, displaying them as clean green numbers in the corner of Kael's peripheral vision. The interface also tracked something it called the Humanity Index, a score from zero to one hundred that measured how many baseline human traits a person still possessed. When Kael-7 was born in 2063, their Humanity Index had been ninety-four. After the respiratory enhancement at HelixPoint, it was eighty-seven.

The domed sectors of London had been built in the 2040s, after the Thames Barrier failed and the North Sea poured through the gap like a judgment from a god that had stopped believing in humanity. The old city still existed beneath the water — the Houses of Parliament, Buckingham Palace, the London Eye, all of them dark and silent, visited only by the gene-spliced divers who harvested metals and artifacts from the drowned streets. The thirty-eight domes were connected by pressurised tubes, and the air in those tubes was filtered through scrubbers that had been maintained past the point of any sensible engineering, kept alive by the desperate ingenuity of people who had nowhere else to go.

Kael-7 lived in Sector Amber, the eighth largest dome, with a population of forty-two thousand. The dome was a half-sphere of reinforced polymer, and its walls were lined with vertical farms that grew algae and soy and the genetically modified fish that constituted the primary protein source for the sector. The light was artificial and never varied, a steady amber glow that gave the sector its name and that everyone who lived there had learned to ignore. The neural interface could filter the light, could make it look like sunlight or moonlight or the neon glow of the old city, but Kael-7 had stopped using that feature years ago. It felt dishonest.

The corruption was first detected in Sector Violet, the smallest and poorest of the domes, where the air scrubbers had been failing for months and the population had been surviving on rations that were ninety percent algae paste. A gene-splicer named Dr. Aris Voss, who ran a clinic in the sector's lower levels, had developed a modification that allowed the human digestive system to extract nutrients from sources that would otherwise be indigestible — the fungus that grew on the dome walls, the synthetic fibers of old clothing, the cellulose in algae that normal human stomachs could not break down. The modification worked. The people of Sector Violet stopped starving. And then they stopped being people.

The mutation spread through the sector's water supply, because Voss had designed it as a contagious modification, a gene drive that would propagate through the population without requiring individual clinic visits. Within three months, eighty percent of Sector Violet's population had the modification. Within six months, their Humanity Index scores had dropped below forty. They could eat anything. They could survive on nothing. They had stopped speaking. They had stopped dreaming. The neural interfaces showed their brain activity patterns shifting, flattening, becoming something that no longer registered as human on the scanners.

Kael-7 was assigned to the investigation team because of their Humanity Index. Eighty-seven was still high enough to be trusted with decisions that required moral judgment, and low enough to survive in environments that would kill a baseline human. The team consisted of five people, each with their own modifications, their own adaptations, their own declining Humanity Index scores. The team leader was a woman named Sera-3 whose muscles had been reinforced with carbon fiber and whose Humanity Index was sixty-two. The medic was a man named Thorne-11 whose blood had been replaced with a synthetic oxygen carrier and whose Humanity Index was fifty-eight. The engineer was a person named River-5 whose hands had been replaced with multi-tool appendages and whose Humanity Index was forty-nine.

Each modification was a survival choice. Each survival choice was a mutation. Each mutation was a step away from humanity, a step toward something that could survive in the domes but could no longer remember why survival mattered.

The team entered Sector Violet through the pressurised tube connecting it to Sector Indigo, a tube that had been sealed for two months. The air on the other side was wrong — not toxic, not unbreathable, but wrong in a way that the instruments could not measure but that Kael-7 could feel in the part of their brain that still registered human instinct. The dome was dim. The algae farms on the walls had been eaten away, stripped down to the bare polymer. The people were still there — forty thousand of them — but they were not moving. They were standing or sitting or lying on the ground, their eyes open, their neural interfaces flickering with data that made no sense.

"They are still alive," Sera-3 said. Her voice was calm, the calm of someone whose Humanity Index was low enough that the sight of forty thousand catatonic people did not trigger an emotional response. "The gene drive has altered their neural architecture. The brain is still functioning, but the functions it is performing are no longer recognizably human."

"Are they in pain?" Kael-7 asked. It was a human question, the kind of question that came from a Humanity Index of eighty-seven. Kael-7 was surprised to find that they still cared about the answer.

"The concept of pain requires a self to experience it," Sera-3 said. "They no longer have a self."

The investigation took twelve days. Kael-7 spent those twelve days walking through the silent streets of Sector Violet, talking to the few people who had not yet lost the ability to speak, the ones whose Humanity Index scores were still in the forties and fifties. These people were terrified. They could feel the change coming. They described it as a kind of fading, a gradual loss of the things that had made them who they were — memories first, then emotions, then desires, then the sense of being an individual separate from the crowd. They were becoming a collective organism, a hive mind that did not think or feel or want but simply existed, absorbing nutrients from the walls and the air and the synthetic materials of the dome itself.

"Dr. Voss did not intend this," one of the survivors said. Her name was Mira-2, and her Humanity Index was forty-four. She was a geneticist who had worked in Voss's clinic. "The gene drive was designed to solve the hunger. It was not designed to alter consciousness. But the digestive changes required neural rewiring, and the neural rewiring had side effects, and the side effects were not detectable until it was too late."

"Voss knew," Kael-7 said. "Voss knew about the side effects."

Mira-2 did not answer. She did not need to. Her neural interface flickered, and the data stream that showed her brain activity flattened for a moment, and Kael-7 understood that she was choosing not to speak, choosing to protect the man who had destroyed her sector, choosing because she still could choose, because her Humanity Index was still forty-four, because she was still human enough to be loyal and human enough to be afraid.

Kael-7 found Dr. Aris Voss in his clinic on the fifth day. He was sitting in his office, surrounded by monitors that displayed the Humanity Index scores of every person in Sector Violet, watching the numbers decline. His own score was thirty-one. His eyes were the color of the dome walls, flat and gray and incapable of focusing on any single thing for more than a second.

"I was trying to save them," Voss said. His voice was distant, the voice of someone whose vocal cords were producing sound without the brain having decided what to say. "The hunger was killing them. The algae paste was insufficient. The fish stocks were declining. They were starving, and I could stop it."

"By turning them into something that is no longer human?"

"The human body is not designed for this environment. The human mind is not designed for this environment. We have been adapting piecemeal for decades — a respiratory enhancement here, a digestive modification there — but the adaptations are competing with each other. The system is unstable. What happened in Sector Violet was inevitable. If not my gene drive, then something else. The whole city is a genetic time bomb."

Kael-7 looked at the monitors. Forty thousand Humanity Index scores. The highest was forty-seven. The lowest was twelve. The average was twenty-nine and falling. At zero, the neural interfaces would stop registering the subjects as human at all — they would be classified as a new species, an organism that had evolved beyond the category that the interfaces were designed to measure.

"How long?" Kael-7 asked.

"Two weeks. Maybe three. The rate of decline is accelerating. The adaptations are compound. Each one enables the next. The organism is optimizing for survival in an environment that does not require consciousness. Consciousness is expensive, in biological terms. It consumes energy. It produces nothing that the environment rewards. Evolution is selecting against it."

The choice came on the eighth day. Kael-7's team had completed its investigation and submitted its report to the Sector Council. The report recommended immediate quarantine of Sector Violet and the development of a gene therapy that could reverse or slow the mutations. But the Sector Council — the thirty-eight representatives who governed the domed city, one from each sector — could not agree on a course of action. The representatives from the wealthier sectors wanted permanent quarantine, a sealed dome that would contain the contagion. The representatives from the poorer sectors, whose own populations were suffering from the same malnutrition that had driven Voss to create his gene drive, wanted access to the modification, wanted the ability to survive without food.

The debate lasted five days. In that time, Sector Crimson reported its first cases of the mutation. Then Sector Amber. Then Sector Indigo. The gene drive had escaped Sector Violet through the pressurised tubes, through the shared water supply, through the genetic material that circulated through the city like a rumor, invisible and unstoppable.

Kael-7 returned to Sector Amber on the thirteenth day. Their own Humanity Index was eighty-three now — the prolonged exposure to the contaminated environment in Sector Violet had accelerated their mutation rate, and the respiratory enhancement they had received at HelixPoint had made them more susceptible to the gene drive's neural effects. They could feel the change beginning. It was not painful. It was not even unpleasant. It was a kind of calm, a kind of acceptance, a gradual fading of the anxiety that had defined their life in the domes. They stopped worrying about food. They stopped worrying about air. They stopped worrying about the future.

The neural interface displayed a warning: Humanity Index 79. Recommended intervention: immediate gene therapy. Kael-7 dismissed the warning. They were not sure why. The part of their brain that wanted to survive was still functioning. The part of their brain that wanted to be human was beginning to fade.

They went to see their mother. Kael-7's mother was a baseline human — no modifications, no enhancements, a Humanity Index of ninety-eight. She lived in Sector Emerald, the dome reserved for the elderly and the unmodified, a museum of the old world where the light was set to mimic natural sunlight and the algae farms were hidden behind false walls that looked like the English countryside. Kael-7's mother was seventy-two years old, and she was dying of a cancer that the gene-splicing clinics could have cured if she had been willing to accept the modifications. She had refused. She had chosen to die as what she was rather than live as something else.

"You are changing," she said. She was lying in a bed in the Emerald hospice, her face lined with age and illness, her eyes still the bright blue that Kael-7 remembered from childhood. "I can see it in your face. You are becoming like the others."

"I am surviving," Kael-7 said.

"That is not the same thing."

"It is the only thing that is the same. Everything else is a luxury. Dreams, memories, the sense of self — these are things that evolution will discard if they are not useful. They are not useful here. The domes do not reward consciousness. They reward adaptation. The ability to survive on nothing. The ability to exist without wanting."

"Then what is the point of surviving?" Kael-7's mother asked. "If you survive by becoming something that is not you, then who has survived?"

Kael-7 did not answer. They could not answer. Their Humanity Index was seventy-one now, and the question required a kind of reasoning that was becoming difficult. They could still understand the words, still parse the syntax, still process the logical structure of the question. But the emotional weight of it — the grief in their mother's voice, the accusation, the plea — was fading, becoming distant, becoming irrelevant.

The final choice came three days later. The gene therapy that the Sector Council had finally approved was available at every clinic in the city, a one-time treatment that could reverse the mutations and restore the Humanity Index to its original baseline. But the treatment had a side effect. It would undo all modifications, not just the ones from the gene drive. The respiratory enhancements. The digestive modifications. The neural interfaces. Everyone who took the treatment would become baseline human again — fully human, fully vulnerable, fully incapable of surviving in the domed city that they had built.

Kael-7 stood in a clinic in Sector Amber, holding the injector that contained the gene therapy. The injector was cool in their hand. The neural interface displayed a choice: Accept treatment — Humanity Index will restore to 94. Estimated survival probability in current environment: 12%. Or: Reject treatment — Humanity Index will continue to decline. Estimated time to zero: 9 days. Estimated survival probability at zero: 89%.

The numbers were clear. The mathematics of evolution were clear. Survival favored the mutation. Humanity favored the treatment. Kael-7 could be human and die, or become something else and live.

They thought about their mother, choosing cancer over modification, choosing death over transformation. They thought about Aris Voss, watching the numbers decline on his monitors, having already lost enough of himself that the tragedy no longer registered as tragedy. They thought about the forty thousand people in Sector Violet, standing or sitting or lying on the ground, their eyes open, their brains performing functions that no longer included thought or feeling or desire.

They thought about justice. Justice was a human concept. Justice required a self to want it, a self to demand it, a self to fight for it. The gene drive was erasing justice along with everything else. There would be no trial for Aris Voss. There would be no reckoning for the decisions that had destroyed Sector Violet. There would be no accountability, no punishment, no recognition of the crime. There would only be adaptation, and survival, and the slow, steady decline of everything that had once made people human.

Kael-7 pressed the injector against their arm. The neural interface displayed one final warning: This action will reduce survival probability by 77%. Do you wish to proceed?

They pressed the button.

The treatment took twelve hours. Kael-7 spent those twelve hours in a medical bay in Sector Amber, their body convulsing as the gene therapy undid the modifications that had kept them alive in the domes. The respiratory enhancement dissolved, and their lungs began to struggle with the methane-tinged air. The digestive modifications reversed, and their stomach cramped at the thought of algae paste and synthetic protein. The neural interface flickered and died, and for the first time since birth, Kael-7 saw the world without the green numbers in the corner of their vision. It was terrifying. It was painful. It was human.

When it was over, Kael-7's Humanity Index was ninety-four. Their estimated survival probability was twelve percent. They did not know how long they would live. They did not know if the choice they had made was the right one. They knew only that they could dream again, and that the dream they had, on the first night after the treatment, was a dream of the old London — the London above the water, the London of sunlight and rain and people walking on streets that were not pressurized tubes, the London that had existed before the choices that had led to the choices that had led to the domes and the mutations and the slow extinction of the human.

Behind every adaptation lies a choice. Behind every choice lies the question of what we are willing to lose in order to survive. The domes had been built to preserve humanity, but humanity cannot be preserved by becoming something else. Justice requires a self that wants it. Mercy requires a self that can feel it. Love requires a self that can recognize another self, separate and precious and irreplaceable. The gene drive had erased all of these things, and in doing so, it had achieved a kind of perfection — an organism that could survive anything, because it no longer had anything to lose.

Kael-7 chose to lose everything. They chose to be vulnerable. They chose to be human, knowing that human was a category that might not survive. The neural interfaces tracked the numbers, and the numbers said the choice was irrational, and the numbers were right. Justice is irrational. Mercy is irrational. Love is irrational. These are not survival strategies. These are the things that make survival worth wanting.

In the flooded tube stations beneath the domes, the gene drive continued to spread. The Humanity Index scores continued to fall. The city continued to adapt, to evolve, to become something that no longer dreamed or remembered or wanted. But in Sector Amber, in a medical bay that smelled of antiseptic and algae, Kael-7 lay in the dark and dreamed of sunlight on water, of rain on stone, of a city that had not yet learned the cost of survival. The dream would not help them live. The dream would not feed them or protect them or make them stronger. The dream was a luxury, an expense, a remnant of a brain that evolution was selecting against. But it was theirs. It was human. And as long as they could dream, they could still believe that humanity was worth the cost of being human.