Bryan Caplan  

Good News About Subsistence

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Robin's sounding strangely like a doom-sayer* lately:
But as long as enough people are free to choose their fertility... then in the long run we should expect to see a substantial fraction of population with an heritable inclination to double their population at least every century.  So if overall economic growth doubles less than every century, as I've argued it simply must in the long run, income per capital must fall over the long run, a fall whose only fundamental limit is subsistence; we can't have kids if we can't afford them.
For flesh-and-blood lives, as opposed to vivid simulations, I actually agree with Robin.  But there are important - and heartening - caveats that I think (?) he accepts, but isn't pushing:

1. The fact that repeatedly doubling the human population will eventually reduce per-capita income does not show vastly increasing it would reduce per-capita income.  As I said before:
"It has to stop sometime" was as true when our population was 10,000 as it is today.  But as far as we can tell from the simultaneous rise of population and per-capita income, "sometime" is a long way off.
2. As Landsburg has argued, if you don't like your family's per-capita income, you can unilaterally raise it by having fewer kids.  If you're worried that your neighbors' breeding is reducing your kids' expected wages, take the money you saved by having fewer kids, and set up a trust on their behalf. Just make sure that the trust invests in capital, land, and/or other assets that go up in value as population rises. 

Of course Robin could point out that in the long-run, people who use these strategies will become a small fraction of the population.  True enough.  But the total number of descendants of less fertile people doesn't have to decline over time.  As long as your dynasty doesn't fall below replacement, following my proposed strategy implies merely that your descendants will be increasingly outnumbered, not that they'll go extinct.

3. You have to be careful with the word "subsistence."  It's true that eventually the relative price of kids will be so high that the average person will only be able to physically sustain two.   But people in this "subsistence" regime could still have awesome entertainment, art, science, blogs, virtual reality, and so on.  The relative price of fitness-reducing consumption will fall over time.  Implication: In Robin's seemingly frightening scenario, anyone willing to forego a child could consume a massive bundle of fun stuff instead.

In short, the best way to explain Robin's claim isn't that our descendants will be "forced" to slave day and night to feed hungry mouths.  Rather, it's that our descendants will care a lot more about kids than we do.  However, if one of your quirky descendants wants a different kind of life, it will still be well within his budget set.

* As far as I understand, Robin cares about aggregate, not per-capita welfare.  So he would deny that he's being a doom-sayer.


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COMMENTS (9 to date)
Norman writes:

With these caveats, particularly the third, I think I can agree with the argument. I think a big part of what is missing in Robin's version is the idea that having children is constrained by both income and relative price, not just income alone (which is the usual final destination of Malthusian arguments, and why I never put much stock in them).

I'm still a bit put off by the idea that technological growth is constrained by numbers of atoms, which I think fundamentally misinterprets the nature of knowledge, but with the relative price of children and the "outside option" included, this becomes less of an issue.

Toon India writes:

well, the meaning of 'subsistence' will change drastically for the middle class.. now subsistence for the middle class also includes so I guess the next generation will have lesser kids will they will have resources per capita.

Awesome blog!!

JPIrving writes:

Doesn't each new person have two hands and a brain? Why can't they use capital (with increasing performance/price ratio)to grow GDP/head? Who cares if it hits a wall in 5k years, as long as we get immortality and rocket cars?

Ray Kurzweil says that the end result of the exponential growth in technology, will be to convert all matter in the universe into a single "living" machine. I think if we reach that point and can't grow anymore, we can be content in the achievement :)

Blackadder writes:

Prof. Hanson's argument against economic growth continuing indefinitely was that there just weren't enough atoms in the universe for this to happen. Would the same hold for population growth?

eccdogg writes:

What makes Hanson so confident that he knows for certain the number of atoms in the universe or that it is finite?

I know that modern physics has established beliefs about those values based on a combination of empircism and theory, but certainly there is a probability greater than zero that the conventional wisdom is wrong when we are considering a vast space of which we only inhabit an infintesimal fraction.

Granite26 writes:

Of course Robin could point out that in the long-run, people who use these strategies will become a small fraction of the population. True enough. But the total number of descendants of less fertile people doesn't have to decline over time. As long as your dynasty doesn't fall below replacement, following my proposed strategy implies merely that your descendants will be increasingly outnumbered, not that they'll go extinct.

Libertarian Wonderland, that... Say you do the investing in capital bit, and your kids do get your proportion of productivity over their smaller numbers down the line. A few generations later, the breeders vastly outnumber your decendants, who own (per capita) a disproportionate percentage of the resources.

Modern history has proven that that situation 'isn't fair' and that the wealth will need to be 'shared', and that's only in a peaceful democracy setting.

Andy McKenzie writes:

Bryan, you wrote, "following my proposed strategy implies merely that your descendants will be increasingly outnumbered, not that they'll go extinct."

You're assuming that individuals from your trust-fund protected descendants and the other group of higher-breeding individuals will not cross lines and have children. That seems unlikely and if carried out to its logical extreme would lead to expressing recessive mutations and reduce fitness among the small interbreeding population.

Overall I agree with you as compared to Robin, however. That's because because genetic engineering is going to be commonplace in at most 500 years and will make his arguments about the personalities that will survive basically moot.

Doc Merlin writes:

This is silly, the most useful in the long run, resource is human creativity. This whole thing in nonsense in any reasonable period of time. Sure, 1k years from now, it might be an issue, but now its not. However, I can't really predict what technology will be 100 years from now, much less 1000 years, so, I will chalk this whole exercise up to silliness.

Tim Tyler writes:

Re: 'Of course Robin could point out that in the long-run, people who use these strategies will become a small fraction of the population. True enough. But the total number of descendants of less fertile people doesn't have to decline over time. As long as your dynasty doesn't fall below replacement, following my proposed strategy implies merely that your descendants will be increasingly outnumbered, not that they'll go extinct.'

You need an exponentially increasing population for that to work.

An exponentially increasing population seems unlikely - since spatial resources apparently increase at most according to t cubed.

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