“Mammals, fish, whatever,” said Rad. “My point is, those tiny land animals became the biggest things in the ocean.”

“It’s the best-documented example of macroevolution in the fossil record.” Marty stifled a yawn. “The buoyancy of water prevents growth restrictions, and the bigger you are, the easier it is to stay warm.”

“And whales need to stay warm because they’re warm-blooded?”

“That’s right.”

“Merfolk are mammals too…”

He sighed. “What are you getting at, Rad?”

“Well, merfolk are warm-blooded and need to keep warm too. You mentioned in the documentary they’ve been spotted all over the world, not just in tropical waters. So…maybe merfolk are gigantic, like whales? Or at least a lot bigger than us?”

“You saw the skull. It was the same size as yours or mine.”

“It could have belonged to an infant.”

Marty rubbed his forehead, sensing a headache looming. “I doubt that very much.”

“Why?”

“I just do.”

“Come on, Marty! Humor me. I think I’m onto something. This is a totally feasible—”

“It’s not,” he told her curtly. “Look, whales as you think of them started inhabiting the oceans forty to thirty million years ago, okay? They were solitary animals, and there were some damn big predators in the oceans then. Being large helps an animal keep warm, but it’s also a good deterrent against getting eaten. That’s perhaps the most important reason why whales grew so large. Merfolk, on the other hand, are presumably intelligent and social, like us. A more fitting aquatic equivalent would be dolphins, which are intelligent and live in pods with strong social bonds. They work together to hunt and deter threats. They don’t need to be the size of a house to get by.”

The flight attendant parked the service trolley in the aisle next to them. Rad ordered a coffee with sugar and cream, while Marty demurred.

“Yes, he’d like a coffee too, please,” Rad insisted.

“No, I would not, thank you,” he said.

“Okay, two for me then.”

The flight attendant poured two coffees, set them on Rad’s fold-down tray, and moved on to the next row of passengers.

“I told you I don’t want one,” Marty told her.

“Ow! Too hot!” she said, sipping one of the coffees and setting it back down on her tray. “I ordered you one because I know you too well, Marty. You’re going to see me enjoying mine, and you’re going to ask for a sip. I’d rather you just have your own.”

“I’m not going to ask for a sip.”

“You always take food off my plate when we’re out for dinner.”

“That’s different.”

“You also finish my alcohol if I don’t want it.”

The looming headache began to throb, and it wasn’t solely from being tired and hungover. Rad could be maddening sometimes. Still, he probably should have asked the flight attendant for a glass of water.

“Are you my fan, Marty?”

“What?”

“Are you my fan?”

“Of your show?” He shrugged. “I watch it…sometimes.”

“So you’re my fan?”