Robert Heinlein and the basic theorem of population mechanics.

It’s been a project of mine, over the last few months, to catch up on some of Robert Heinlein’s less-famous books that I never got around to reading as a youthful sci-fi fan. That’s how I happened to be reading his 1950 novel Farmer in the Sky on the same day that I saw this Jordan Weissmann article on the Atlantic website about solving America’s demographics problem.

The problem is that the fertility rate in the United States has recently fallen below replacement level. That level in developed countries is around 2.1 children per woman – one baby to replace the mother, one to replace the father, and an extra fraction of a baby to cover accidental deaths. Below that level, barring immigration, a population will gradually contract. The problem isn’t contracting population per se. It’s that as fewer children are born, the ratio of working adults to non-working senior citizens tips toward the latter. With fewer workers, the economy can’t produce enough wealth to support its growing complement of seniors in the state of comfortable retirement they’ve come to expect.

Weissmann’s solution is straightforward – America just needs to bring in more immigrants. He needles the New York Times‘ Ross Douthat for his recent musings on the fertility problem which declined to endorse the open-borders approach Weissmann favours.

If America wants to stay productive, it’s hard to see how it (and other developed countries in the same demographic boat, like Canada) can avoid taking in more newcomers. As Weissmann argues, in the short run it’s probably necessary. But in the long run, reversing demographic decline isn’t a simple matter of slapping a welcome mat by the abandoned border checkpoints. First off, the decline isn’t limited to the developed world. The United States, Canada, and Western Europe are joined on the vanishing side of the 2.1 cutoff line by traditional people-exporters like China, Vietnam, and Iran. India’s fertility rate is 2.58 and falling fast – that’s about what the U.S. rate was in the 1960s. Mexico’s is down to 2.27.

In the past these countries were happy to watch their surplus population drained off via emigration to the West. If current trends continue, it won’t be long before they feel the demographic crunch too. They’ll begin offering incentives to keep their brightest and most ambitious young people at home. America will be obliged to compete against other rich countries, most of them in much direr demographic straits, for a shrinking pool of potential immigrants.

The West will have no difficulty recruiting newcomers, not anytime soon. But these newcomers will be harder to assimilate than ever before. If we want to bring them in sufficient numbers to counter demographic trends, there will simply have to be more of them than we’re used to – a larger lump dropped in the melting pot all at once. And the composition of the lump will resist mixing. Up till now we could take our pick of striving geniuses stifled by a lack of opportunity in their crowded home countries. Increasingly we’ll have to hustle for a share of the dissatisfied B-students whose countries couldn’t be bothered to make an effort to retain them. The easiest to recruit will be those from the poorest, most chaotic, and most fecund countries. They’ll be less literate, slower to pick up the language, more alien to the existing culture than previous immigrants. Being generally ill-educated, they’ll compete for jobs with the poorest slice of the native-born population, driving down the cost of unskilled labour and exacerbating income inequality.

Eventually, most likely, the West will absorb and be fortified by the immigrant wave, as it has previous waves. But it’s not such a cost-free operation as Weissmann implies. And once fully assimilated, the newcomers will be just as apathetic about reproducing as the rest of us.

What does all this have to do with Robert Heinlein? Here’s Paul du Maurier, an incidental character in Farmer in the Sky, discussing population projections with a fellow colonist on Jupiter’s moon Ganymede. They’re debating how many ex-Earthlings their growing colony can accommodate:

“Studied any bionomics, Bill?”
“Some.”
“Mathematical population bionomics?”
“Well – no.”
“But you do know that in the greatest wars the Earth ever had there were always more people after the war than before, no matter how many were killed. Life is not merely persistent, as Jock puts it; life is explosive. The basic theorem of population mathematics to which there has never been found an exception is that population increases always, not merely up to the extent of the food supply, but beyond it, to the minimum diet that will sustain life – the ragged edge of starvation. In other words, if we bled off a hundred thousand people a day, the Earth’s population would then grow until the increase was around two hundred thousand a day, or the bionomical maximum for Earth’s new ecological dynamic.”

This lump of unleavened Malthusianism represents the best wisdom of the forward-thinkingest slice of the American intelligentsia circa 1950. In science-fiction from that era, unconstrained population growth is simply assumed. That was why all those intrepid space cadets blazed their trails to the stars in the first place – so that humanity’s teeming hordes could be deposited on the snowy plains of Ganymede, making room for more babies back home. It would never have crossed Heinlein’s mind that the Ganymede colony might have trouble attracting qualified geo-engineers because the aging home planet refused to let them emigrate.

I don’t read enough modern fiction to know if Heinlein’s successors are contemplating, as he did, the dystopian possibilities of current population trends. My sense is that the so-called demographic death-spiral has been relatively neglected, compared to the attention the population bomb got fifty years ago. I can think of a couple of recent-vintage sci-fi stories that are still built around population-bomb assumptions, but the only death-spiral story I know of is P.D. James’ allegorical The Children of Men, discussed in the article linked above. (I reviewed the entertaining but largely off-point film adaptation a few years back.)

Why has the death-spiral been neglected? For starters, many well-informed people seem oblivious to the direction the demographic arrow is now pointing. Secondarily, there’s an ideological bias at work. While death-spiralers are noticeably clustered on the political right, population-bombers tend to be on the left. Among the latter, there seems to be a widespread feeling that if we do dwindle away, hell, who’d miss us. Take this recent article in the New Yorker on the ethical implications of having children. Elizabeth Kolbert blandly quotes the philosopher David Benatar, who is untroubled by the prospect of human extinction:

“Humans have the unfortunate distinction of being the most destructive and harmful species on earth,” he writes. “The amount of suffering in the world could be radically reduced if there were no more” of us.

…But she’s openly skeptical of the economist Bryan Caplan’s suggestion that maybe having kids is, you know, a good thing:

“More people mean more ideas, the fuel of progress.” In a work that’s full of upbeat pronouncements, this is probably his most optimistic, or, if you prefer, outrageous claim.

Until recently that “outrageous claim” was held nearly universally. In a few rich countries it appears already to be the minority view. How much longer will it hold sway in the rest of the world?

The United Nations’ 2004 report World Population to 2300 projects the planet will peak at 9.22 billion people in 2075, then stabilize at around 9 billion. But that projection assumes fertility rates will do something weird:

[F]ertility will fall in all countries below replacement (in the medium scenario) and rebound to replacement after a period largely similar across countries of a century or so.

It’s obvious enough why the UN is projecting fertility rates to fall – that’s what they’re doing already, pretty much everywhere; the only question is whether they’ll plummet in the developing world to the depths they’ve reached in the rich countries. But what about the UN’s assumption that after a seemingly arbitrary period of “a century or so”, fertility will “rebound”? Is there any reason to suppose this will happen in the countries that have already fallen below replacement level?

Is it reasonable to expect fertility to rise from current levels? It is impossible to tell, but one can consider the implications if it does not. … By 2300 … [a]bout half the countries of Europe would lose 95 per cent or more of their population, and such countries as the Russian Federation and Italy would have only 1 per cent of their population left. Although one might entertain the possibility that fertility will never rise above current levels, the consequences appear sufficiently grotesque as to make this seem improbable.

As near as I can tell, this is the only explanation in the report for the assumption that in the long term, fertility rates will “rebound” to replacement level: It would be “grotesque” if they didn’t. Well, there you go.

The UN recognizes, and Farmer in the Sky demonstrates, that you can’t simply project current trendlines until they slope off the edge of the graph. Who knows, maybe there’s another baby boom right around the corner. Or maybe not. Robert Heinlein imagined that mankind was cursed with a biological imperative to overbreed, and that with a little gumption we would escape this curse by conquering the stars. But what if our imperative is nothing more than a polite suggestion, and our real curse is that, given the choice, few of us bother to heed it?

M.

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I’ve been kvetching about this issue for years, most recently in a 2010 post about how the future will belong to fast-breeding religious conservatives.

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Update, July 27, 2020: Redirected a couple dead links, added cover image, and linked to Bibliography page.