“And all these examples became parables in the sixties and seventies because everybody thought that something of the same sort was going to happen to us,” Lisa finished for him. “I see.”

“If only,” Miller said. “What actually happened was that a few strident alarmists began telling people that something of the sort was bound to happen to the human population if we didn’t take measures to prevent it, and take them soon.For five years or so, a few people listened, and crew anxious—and then even they decided that by far, the easiest way to stave off the anxiety was not to listen to the alarmists. So they played the proverbial ostrich and stuck their heads in the sand. They were encouraged to do it by economic theorists who # thought that economic growth was the only worthwhile goal of collective human endeavor, and that population growth was good because it facilitated economic growth. Ironically enough, the original founders of Mouseworld were also anti-alarmists.”

Lisa hadn’t been expecting that, and she couldn’t take advantage of the pause that Miller left for her to pick up the baton and carry the argument forward.

“After Calhoun’s demonstration,” Miller continued, “other researchers tried to repeat his experiment using mice, which were more convenient by virtue of their smaller size. McKendrick was one of those researchers. The other experiments duplicated Calhoun’s findings, and so did some of McKendrick’s populations, but McKendrick also found some exceptions. Some of his mouse populations didn’t exhibit the standard boom/crash scenario. They adapted their behavior to a much higher population density than their wild cousins were used to. There was still a certain amount of nastiness, but they managed to limit their breeding without overmuch cannibalism, and the increase in mortality that helped bring the two into equilibrium was achieved without overmuch fighting.”

“I get it,” Lisa said. “Mice are meek, like snowshoe hares, while rats are more like lemmings.”

“That’s part of it,” Miller agreed. “But it’s not the whole story. Snowshoe hares may be meek, but they still go through boom-and-crash cycles. Nobody knows for sure, but the more important distinction might be that when rat numbers explode in the wild, they’re usually cut back by disease—as witness the Black Death. Calhoun’s rats were flea-free, of course, so they didn’t suffer the same check. Plagues of mice are more commonplace than plagues of rats, especially in limited spaces, but there doesn’t seem to be an external limiting factor that kicks in—not reliably, at any rate. For that reason, mice seem to have evolved their own internal limiting mechanisms. Because the mechanism is activated only under exceptional circumstances, which may occur only once in a hundred or a thousand generations, a lot of strains lose it to genetic drift—but enough retain it to gain a selective benefit when the conditions do arise. The same is true of some insects that became human commensals as soon as the first agriculturalists began cultivating wheat and rice. The grain beetles, for whom a field of wheat was Utopia and a granary Seventh Heaven, have relatively efficient internal mechanisms of population control, which can stabilize their populations and protect them from the devastations of boom/crash cycles.

“Storytellers in search of more reassuring parables argued that if mice were smart enough to avoid the worst effects of overpopulation, ultrasmart humans ought to be able to do it too. They chose to ignore the fact that it wasn’t intelligence that was enabling McKendrick’s luckier mice to do what they did. They also chose to ignore the fact that humans haven’t gone through nearly enough generations since the first human population crisis to begin to develop the kind of facultative response that the luckier mice possessed.”

“And these are lucky mice?” Lisa asked, waving her hand in a broad semicircle to encompass as much of Mouseworld as she could.

“They are now,” Miller confirmed. “To begin with, all four populations boomed and then crashed, and then went through the whole cycle again—but after the second crash, the more adaptable mice had come into their inheritance. Since then, all four populations have stabilized. Imagine that: London, Paris, Rome, and New York, all marching in step toward a common goal! Inspiring, in its way, but no real cause for congratulations. The mice have been intensively studied, of course, to see exactly how they work the physiological tricks that allow them to stabilize their populations, in the hope that science might provide for humans what natural selection probably hasn’t—but given that we areso smart, it seems ridiculous to try to duplicate the admittedly imperfect methods of mindless mice, don’t you think?”

“I don’t know,” Lisa said. “It depends. If intelligence produces a political solution to the problem, that would be a triumph. But if it doesn’t … mightn’t it be a good idea to have a biological solution as backup?”

“If only it were that simple,” Miller replied sadly—but he didn’t seem in the least scornful of her suggestion. “Alas, if our intelligence is inadequate to facilitate a purely social solution, it can hardly be expected to facilitate the social application of a biological one. People who refuse to use contraception for the sake of the common good are hardly likely to accept institutionally imposed sterilization, are they?”

“Actually,” Lisa said, grateful that the training she’d recently undergone was useful for something, “that’s not as obvious as it seems. People accept policing to the extent that they do because they admit the necessity of restraint and want it imposed uniformly and fairly. All motorists routinely break the speed limit and park their cars wherever they can, and they all get mad if they’re caught by radar or ticketed by a traffic officer, but they all accept the fundamental necessity of speed limits and parking restrictions.”

“That’s a fair point,” Miller conceded, “and the comparison is probably more relevant than it seems, given that so many people seem to care at least as much about their cars as their children. I can see that you’ll be a considerable asset to my seminars on the neoMalthusians. Maybe you can take them over next year. But you mustn’t allow yourself to become too entranced with Mouseworld. Whatever its running costs may be, they’re trivial compared to the time it can soak up. Whatever you do, don’t volunteer to help with the counting or the data processing. As far as the production of interesting results is concerned, the cities ran into the law of diminishing returns ten years ago. No matter how long they may continue, each hour invested in their observation will produce less and less reward as time goes by. You and I, Lisa, must concentrate our attention on events on a much smaller scale. DNA is the key to everything: all biological understanding and all bio technological possibility. Can we move on now?”

She couldn’t help noticing that it was the first time he had spoken her name. She was slightly ashamed of herself for caring, but she figured that she could probably forgive herself, if the need arose.

In spite of Morgan Miller’s advice, Lisa couldn’t help being fascinated by Mouseworld. She was relieved to discover that she wasn’t the only one and that its captivating influence wasn’t confined to fledgling research students. Chan Kwai Keung was already in his second year of postdoctoral study, having committed himself to the long rite of passage by which aspiring university scientists had to spend the early phases of their careers working on short-term contracts for derisory salaries. His stature was a little shorter than Morgan Miller’s, and no slimmer than Lisa’s, but he moved with an economical grace that made him seem far less obtrusive than either of them. He always had a book in his hand, but Lisa suspected that the habit had as much to do with an obsessive need to have a kind of retreat permanently available as with any desire to cultivate an image as the most studious apprentice in the department’s junior ranks.