“Yes. Depth of chests have grown greater, I read.”

She laughed again. “The thin air, right?”

“Presumably. It’s true in the Andes, anyway. The distances from spine to sternum in Andean natives are nearly twice as large as they are in people who live at sea level.”

“Really! Like the chest cavities of birds, eh?”

“I suppose.”

“Then add big pecs, and big breasts. . . .”

He didn’t reply.

“So we’re evolving into something like birds.”

He shook his head. “It’s phenotypic. If you raised your kids on Earth, their chests would shrink right back down.”

“I doubt I’ll have kids.”

“Ah. Because of the population problem?”

“Yes. We need you issei to start dying. Even all these new little worlds aren’t helping that much. Earth and Mars are both turning into anthills. You’ve taken our world from us, really. You’re kleptoparasites.”

“That sounds redundant.”

“No, it’s a real term, for animals that steal food from their young during exceptionally hard winters.”

“Very apt.”

“We should probably kill you all when you turn a hundred.”

“Or as soon as we have children.”

She grinned. He was so imperturbable! “Whichever comes first.”

He nodded as if this were a sensible suggestion. She laughed, although it was vexing too: “Of course it will never happen.”

“No. But it won’t be necessary.”

“No? You’re going to act like lemmings and run off cliffs?”

“No. Treatment-resistant diseases are appearing. Older people are dying. It’s bound to happen.”

“Is it?”

“I think so.”

“You don’t think they’ll figure out ways to cure these new diseases, keep stringing things along?”

“In some cases. But senescence is complex, and sooner or later. . . .” He shrugged.

“That’s a bad thought,” Zo said.

She stood, pulled the dried fabric of her singlet up her legs. He stood and dressed too.

“Have you ever met Bao Shuyo?” he asked.

“No, who’s she?”

“A mathematician, living in Da Vinci.”

“No. Why do you ask?”

“Just curious.”

They hiked uphill through the forest, from time to time stopping to look after the quick blur of an animal. A big jungle chicken, what looked like a lone hyena, standing looking down a wash at them. . . . Zo found she was enjoying herself. This issei was unteasable, unshockable; and his opinions were unpredictable, which was an unusual trait in the old, indeed in anyone. Most of the ancient ones Zo had met seemed especially bound in the tightly warped space-time of their values; and as the way people lived their values was in inverse proportion to how tightly they were bound in them, the old had ended up Tartuffes to a man, or so she had thought, hypocrites for whom she had no patience at all. She despised the old and their precious values. But this one didn’t seem to have any. It made her want to talk more with him.