Even before the applause had faded away, an old, balding rat was scurrying across the auditorium to overtake the raven who had given the talk.

“Interesting seminar, Dr Blackfeather,” he shouted. Blackfeather turned, smiling as widely as his beak would allow.

“Hello, Professor Shortfur. Didn’t think you’d be present.”

“Couldn’t miss your talk, could I? Though actually, today, I had a personal interest in the subject. Your theories about the monkey cities are fascinating. Although I hope you know it’ll be an uphill climb to publish them. With fossil evidence of rats and ravens in these cities since antiquity, we’re biased to think we built them ourselves.”

“I find my evidence convincing.”

“It certainly seems like bipedal monkeys did most of the work. But linking the monkeys’ extinction to our species’ rapid cognitive evolution … that’s a brave claim, and one directly relevant to my own research.”

“Indeed? How come the renowned geologist is suddenly investigating brain evolution?”

“It’s a long story. Have you read my paper about how closely the monkeys’ industrial era aligns with rising global temperatures? No? The correlation is nearly perfect. Do you think it’s possible that the Warm Age caused —”

“On such short time scales? Sorry, but that makes no sense.”

“These monkeys make no sense,” Shortfur replied irritably. “Maybe they had a temperature-dependent engineer phenotype? I honestly don’t know, I’m not the evolutionary biologist here. Just saying — the fit’s too good to be a coincidence.”

“Well, correlation is not causation. Maybe … maybe it’s the other way round — the monkeys somehow changed the climate.”

They stared at each other for two full seconds, then both burst out laughing.

“Let’s be serious for a minute,” said Shortfur. “This was a normal species, like us, for millions of years. Then, within decades of the Warm Age beginning, they suddenly all went crazy.”

“By crazy you mean the overpopulation? The monkey-made cities I was talking about?”

“Yes, but also literally crazy. They drove a lot of animals to extinction — ate them, I presume — while at the same time, they were keeping wolves and dinosaurs as pets.”

“If by dinosaurs you mean chickens, we know they harvested them for amino acids.”

“No, I mean actual dinosaurs. Some of the biggest, most ferocious species.”

Blackfeather gaped. “I thought they predate monkeys.”

“Predate as in eat?”

“Predate as in pre-exist. By millions of years, if you trust Beakk’s isotopic analyses.”

“I don’t. Radiometric dating is unreliable around that period. I received some samples from ancient islands in the Pacific, with isotope ratios that Beakk would confidently date as being from the future. Anyway, the fact remains that most dinosaur fossils were found near monkey city centres. Indoors, in huge halls. My point is, monkeys were up to some seriously weird stuff during the Warm Age.”

“And you propose this was somehow caused by the changes in the atmosphere? I’ll have to think about this …”

“Wait, it gets even more interesting. Do you know Dr Whiskers from South Sewer University?”

“Heard of her. An astrophysicist, isn’t she? What’s she got to do with it?”

“As I’m sure you’ve heard, her team’s lunar probe brought back some suspected organic matter last year. They isolated something that might be DNA and sent it to my department for sequencing. I saw the results this morning. Guess what it was.”

“No way. You’re making this up.”

“I swear I’m not. The DNA was too ancient to pinpoint the species, but the conditions preserved it perfectly, and it’s a primate alright. On the Moon.”

“Nonsense. They haven’t got any wings.”

“Damned if I know how they got there, but it’s them. No other primate species was ever smart enough to get all the way up there. And then within a couple centuries they were gone, which, according to your superb talk, sparked our own cognitive evolution and current societies. What do you make of it?”

“You think they all sailed off into the sky.”

“Don’t tell me what I think. What do you think?”

“Do you want my honest opinion?”

“Always.”

“You seem confident in the DNA evidence, so I’ll accept your claim that they landed a monkey on the Moon. That’s an incredible discovery in itself, truly exciting. But this act seems to me like their desperate attempt at a last-minute escape, and they’re unlikely to have got much farther. It doesn’t outweigh the evidence — ample evidence — that they simply ran out of resources and died out fighting over leftovers. Maybe the survivors were outcompeted by more intelligent species like rats, ravens and parrots. Maybe they were weakened by the pollution or hunted down by their dinosaurs. The bottom line is, I find it hard to accept that they found a magic solution in the nick of time, then disappeared without a trace.”

“You know what I find hard to accept?” said Shortfur vigorously. “That a species intelligent enough to build the Berlin Sewer and catapult itself to outer space would meet its end like bacteria in a neglected dish. I believe — I want to believe — that some of them made it out, against all odds. That they’re still alive on some strange planet. Watching us, perhaps.”

Blackfeather’s eyes glinted as he placed a friendly wing on the old rat’s shoulder. “I want to believe it too, Professor. But I can do nothing but hope. With your permission, I’ll be returning my attention to Earth, where it belongs.”