I had finished the beer. I let Peter call for another one.

Naked mole rats turned out to be spectacularly ugly little rodents—Peter showed me pictures on his handheld—that live in great underground colonies beneath the African deserts. They have bare, unweathered skin, and their bodies are little fat cylinders, to fit into their dark tunnels.

The mole rats’ favorite food is tuber roots, which they have to go dig for. But the roots are widely scattered. So although they are stuck in cramped conditions underground, it is better to produce a lot of little mole rats than a few big ones, because many little helpers tunneling off to find the roots are more likely to succeed than a few.

“Exactly the conditions where you might expect eusociality to develop,” Peter said. “A situation where you’re forced to live with high population density, limited resources . . .”

Mole rats live in great swarms—and in each colony, of maybe forty individuals, at any one time there is only one breeding pair. The other males simply keep zipped up, but the other females are functionally sterile. They are kept that way by behavior, by bullying from the “queen.”

The workers even have specialized roles—nest building, digging, transporting food. A mole rat will go through several roles as she ages, gradually moving outward from the center. “Some of the ants are like that,” Peter said. “The young serve inside the nest, where they do such chores as nest cleaning. When they get older they serve outside, maybe constructing or repairing the nest, or foraging for food . . .”

For the mole rats, everything works fine until the queen shows signs of falling from her throne. The sterile workers suddenly start to develop sexual characteristics, and there is a bloody succession battle—and the prize for the victor is nothing less than the chance to pass on her genes.

“And that’s why the old fogies are pushed out to the perimeter of the colony,” Peter said coldly. “They are the ones in the front line when a jackal digs up a tunnel—but they are dispensable. You want your young at the center, where they can be quickly deployed to replace the reproductive. But the old ones sacrifice themselves for the sake of the group readily enough. That’s another eusocial trait—suicide to protect others.

“You see what I’m saying. The mole rats are eusocial,” he said. “There is absolutely no doubt about that. As eusocial as any ant or termite or bee—but they are mammals.”

He talked on about mole rats, and other mammals with traces of eusociality—hunting dogs in the desert, for instance. One detail startled me. In the mole rat warrens, the rodents would swarm and huddle to control the flow of air through their passageways. It was just like the Crypt, though I hadn’t told him about Rosa’s antique ventilation system.