OMEYOCAN, THE PLEIADES—Lunch-bound crowds jostled Killa as she crossed the stone plaza between the Seven Towers. Three suns glowed at zenith, warming her skin. Killa smiled to herself as she stopped in the shadow of the Fifth Tower and watched the antics of four tow-headed boys who played at the edge of the reflecting pool. They splashed each other, then dodged behind the obsidian stele that rose from the middle of the pool.
One of their fathers tried to stop their rambunctious play after a volley missed its target and hit two passing women. With a surprised screech, the women brushed droplets from their business suits and hurried away. Even that didn’t catch the attention of the boys’ other three fathers, who stood with their backs to the pool and continued talking without a pause. Across the plaza, Killa saw four toddlers who had the full attention of all their mothers, with one helping each of the dark-haired girls to step across the sun-bathed corridor and avoid tripping the preoccupied adults.
It was such an ordinary, commonplace scene. Each face was repeated in the identical features of multiple siblings, and—of the hundreds of faces Killa saw before her on the plaza—all were female except for the four young boys and their fathers. She knew no one would acknowledge the danger she saw before her. She’d been down that path before.
Reluctantly, Killa turned her back to the plaza and entered the Fifth Tower. She gave her eyes a moment to adjust to the relative darkness and repositioned her portfolio as she gathered her willpower. She hurried across the lobby to the riser and requested the two hundred-sixtieth floor.
Security scanners admitted Killa to the Science Fund office. She settled into a multicolored chair and focused on relaxing the muscles in her neck and back, preparing for a conversation she dreaded. In her mind, Killa could already hear the doubt in Oxomoco’s voice. They’d been friends for almost forty years, since they began their formal training. Her willingness to challenge every hypothesis was one of the reasons Oxomoco made an excellent Science Fund Chair, but it also made conversations with her difficult.
The door slid open and Oxomoco entered the room. She was half-a-head taller than Killa and had startling emerald-green eyes that could pierce you when she was intent on getting her way. Generous silver strands highlighted Oxomoco’s blunt-cut blonde hair, a change since she last saw her. Killa’s own hair had been gray since her early thirties, but she’d always felt it accentuated her dark eyes.
“I’m always surprised to hear from you.” Oxomoco sat across the desk from Killa. “Where does the time go?”
“I often wish I knew,” she replied. “I didn’t want to trouble you with this after all the help you’ve given me over the years, but you’re the only person I know who can make people listen. And someone has to listen.”
“Well, I hope you won’t be disappointed. You know we can always talk, but I can’t do as much as I’d like. I know you’ve barely had enough funding to continue your work since that butterfly incident.”
“Oxomoco, I’m not here about money. I only wish it was that simple. You could say I’m here because of Cipactonal.”
Oxomoco grew very still, her green eyes probing Killa. “What about my son?”
“Let me show you.” Killa pulled a data wand from its case. Oxomoco took it and placed it into the reader. Charts showing test data on the sex-determining region Y gene transformed the wall.
“Ah yes, the SRY gene. This data shows mutations over more than five generations?”
Oxomoco looked at the next set of charts.
“Why are these identical?” As Oxomoco brought of the first set of charts back up so both sets were showing, her back stiffened and her eyes opened wider. Just as Killa predicted when she planned her presentation, Oxomoco didn’t miss the different titles.
“But it shows there’s almost no variation in the Y chromosome.”
“This is the species of butterflies on which you did that talk in Citlalco,” Oxomoco stated flatly, examining the second set of slides. Her voice dropped as she motioned to the first ones. “And this is how humans map?”
Killa nodded. She knew how much Oxomoco wanted it to be wrong. If not for her earlier research on causes of butterfly extinction, she might have missed the significance. Even so, Killa had hoped for another explanation. Just as Oxomoco was doing, her first step had been to display the graphs side-by-side.
“Are you sure this is reliable data?”
“I’m positive. I’ve been trying to disprove it for the past year.” Killa shared the rest of the data. “The human genome has become a sort of battlefield between male and female genes. Of those that survive, ninety-seven percent produce females, just like the butterflies that started my research into the sex-chromosome drive. And you can see that genetic mutations aren’t affecting just butterflies.” She put up the last chart. “I can now show this kind of data on more than two dozen species that have been affected by the sex-chromosome drive in as many years.”
“I guess the pattern was there all along, if we’d just looked,” Oxomoco said.
“How do you think our colleagues will react when data shows the at-risk species is our own?” Killa asked.
Oxomoco stood, walked to the glass wall that faced the plaza and looked down on the activity below. The tense lines around her friend’s eyes and mouth told Killa that Oxomoco felt overwhelmed by what she saw, and by what she didn’t see.
“It’s certainly not news that more females than males have been born for decades—certainly during all of our lifetime,” Oxomoco said.
“That’s true.” Killa joined her watching the women cross the plaza below. “It was just easier to believe it was because pollution increased the estrogen-mimicking chemicals in the body or because of older women bearing children, rather than the result of genetic catastrophe.”
They knew all the rationales—with fertility drugs, instead of one female child, generally three or four were born at one time. Before medical intervention, these children wouldn’t have been conceived. Before scientific advancements in newborn care, they wouldn’t have survived. Now they lived to reproduce. In each generation, more girls grew up with identical sisters as the result of fertility drugs. With fewer males born each successive generation, more boys grew up with cloned brothers.
Pointing to a chart of extinct species, Killa continued, “You can see the research shows a radically different cause. The sex-chromosome drive is a genetic flaw that leads to our extinction, just as it has for at least twenty-three other species in as many years.”
“But why are there so few changes on the Y chromosomes?” Oxomoco returned to her desk and continued to review the data.
“When the sex-chromosome drive is activated, survival of the Y chromosome depends on its being able to hide from the X chromosome,” Killa said. “It’s simple mathematics—females have two X chromosomes and males have one, which gives the X chromosome a three-to-one advantage over males’ single Y chromosome.
“To survive, the Y chromosomes shed as many genes as possible and shut down the rest. They kept genes that enhanced male survival, regardless of their effect on females,” Killa explained. “Over many generations, the male gene only changed in response to X-sweeps, the infrequent mutations aimed at improving conditions for survival of females. The new mutant SRY gene restored the balance for males, if it could.”
“What does this have to do with Cipactonal?” Oxomoco’s tone made Killa think it was a rhetorical question.
“I know how hard it’s been for you—a woman having an only son when most boys are cloned and raised by men,” Killa said quietly. “It’s been a lonely world for Cipactonal. Kids can be even crueler than our colleagues.”
“You think there’s a chance he may not have the sex-chromosome drive because I was able to have him naturally?”
“It’s a long-shot, but one worth looking into. Maybe if you had a daughter…” Killa suggested.
They talked until late in the night. Oxomoco’s position allowed her access to in-depth information on interdisciplinary research going on throughout the system. With Killa’s help, she assembled a research team dedicated to reversing the effects of the sex-chromosome drive.