The Instructions Underneath

The swab kits were still on the bench when everyone else left. Coach Diaz had passed them out at the start of practice, said something about a science partnership and a saliva study, and then a whistle happened and forty kids ran and nobody swabbed anything.

"She forgot to collect them," Soren said. He was reading the little folded paper that came inside the kit. "There's a sample-one and a sample-two tube. You do one before and one after."

Maya was lying flat on the cold floor, breathing like a bellows. "Before and after what."

"Exercise, I think." He turned the paper over. "It says the study is about, hold on. Methylation."

"Methyl what."

"Little tags," Soren said. "On your genes. Chemical tags that sit on the DNA and tell it when to switch on and off."

Maya sat up. "Wait. My DNA is the same in my hair and my toe and my eyeball, right. Same instructions everywhere."

"Right."

"So how does my toe know it's a toe."

Soren stopped reading. This was the thing about Maya. She skipped the paper entirely and went straight to the crack in it.

"Because," he said slowly, "the tags are different in different cells. Same book. Different pages folded down."

"Okay." She grabbed a kit. "So why does a study want spit from a running class."

He read the last panel. Read it again. "It says the tags can change. From exercise."

"They change your DNA?"

"No. That's the weird part." He looked up. "The DNA stays exactly the same. The letters don't move. But the tags on top move. And it says here they've measured it happening after just one workout."

Maya went very quiet. .

"One workout," she said. "Like the one we just did."

"Like the one we just did."

She looked down at her own legs, still pink and hot from the four hundreds. "So right now, in there." She pressed a hand against her thigh. "Something already got rewritten."

"Not rewritten. Re-tagged." Soren was already opening tube one. "We can't do the before part anymore. We already ran. But we're supposed to have two samples and we've got zero, so."

"So we make it a real experiment," Maya said. "Not fake it. We do it right."

They looked at each other. Neither of them had planned to run again.

Maya swabbed the inside of her cheek and dropped the swab in tube one. "There. That's after-the-first-run me."

"Cheek cells, though," Soren said. "The study wants muscle. The tags in muscle are the ones that flip after exercise. Cheek might not do the same thing."

"We can't swab a muscle, Soren."

"I know." He wrote something in his notebook, the pen moving fast across the page, and then he underlined it twice. "But listen. Even if we can't see it in the spit, it's happening. Somewhere in your leg, right now, a gene that helps your muscles use sugar just got its tag knocked off. That's a real one they found. Exercise pulls the tags off certain genes and the genes wake up."

"For how long."

He stopped. "It doesn't say."

Maya stood up. "Then that's the experiment. We run again. Harder. And we see if I feel different, if the second one is easier, because the genes that got woken up the first time are already awake."

"That's not really how you'd measure it."

"I know. But I want to feel the thing the paper is talking about. I want to catch it moving."

So they went back out to the empty track. The sky had gone the orange color it goes right before the lights buzz on. Maya ran the first curve and Soren timed her with the stopwatch on his wrist, and when she came around he read her the number and she made a face and went again.

Third time around she slowed to a walk beside him, hands on her head.

"It's not easier," she said. "My legs are worse. I'm slower."

"Right," Soren said, and there was something careful in how he said it.

"That ruins it."

"No. Think about it." He was walking backward in front of her so he could see her face. "You feel worse. Tired, sore, slow. But the paper says the genes are turning on. So the tired isn't the opposite of the change."

Maya stopped walking.

"The tired IS the change," she said. "The sore is the instructions getting read."

"That's what it looks like."

She stared at her own hands like they belonged to someone smarter than her. "Every single time I've ever felt wrecked after a run. Every time I thought I was just wrecked."

"You were being edited," Soren said.

"By the running." She said it very slowly. "The running reaches down under the letters and moves the tags around and I can't see it and I can't feel the tags, I can only feel the tired part."

Soren nodded. He'd stopped walking backward. They were both just standing on the empty track in the orange light.

"Here's the part I can't get out of my head," he said. "The same DNA. My whole life it's the same DNA. And I always thought that meant it was, like, finished. Written down. Locked."

"But it's not." Maya turned in a slow circle, looking at the track, the fence, the buzzing lights coming on one by one. "It's got a whole layer on top that keeps changing. Every time I do something. The book stays the same and something keeps folding down different pages."

"And nobody assigned which pages." Soren's voice had gone quiet. "You do. By what you do."

Maya thought about the kids who found her too much. Too many questions, too fast, never sitting still. She thought about how none of that felt like a thing she had chosen so much as a thing she was.

"So the me I'm going to be tomorrow," she said, "is partly getting written right now. By this. By being out here doing the second run for no reason except we wanted to catch it."

"By the run you didn't have to do," Soren said.

Maya bent down, unzipped the kit, and took out tube two. She swabbed the inside of her cheek in the last of the orange light, and capped it, and held it up to the lamp so the swab glowed white inside the plastic.