Want to Bet? A Reply to Greg Clark

Greg Clark freely admits that the last two centuries have been wonderful for mankind. But will current trends continue? Clark suggests that they won’t. Growth is a “race between resource costs and scale economies as population grows” and “for 99.9% of human history, up till 1800, the winner in that competition was resource scarcity.” This seems like a telling point: Shouldn’t we base our predictions on all the data instead of the most recent .1% of it?

But how far is Clark willing to take this? The last two hundred years have been unprecedented in countless ways. Population, per-capita income, technology, science, literacy, culture, democracy, lifespan, and international trade exploded. Slavery, monarchy, and death from infectious disease withered away; war itself is poised to join them. Does Clark really expect long-run historical norms to reassert themselves in most of these areas? When you compare the last .1% of human history to the previous 99.9%, there really appears to be a structural break. You don’t have to understand the underlying model to accept this brute fact.

But we can do much better than merely insist, “The modern world is different.” Contrary to Clark, my target essay didn’t merely observe that population and per-capita living standards both sharply increased over the last two centuries. Instead, I built on two widely accepted claims. First: New ideas are the main driver of economic growth. Second: Higher population increases both the supply and demand for new ideas.

Clark is right to name economies of scale as one social benefit of population. But he neglects the far more important effect on innovation. The technological advance that Clark credits for rising abundance of food and energy didn’t come out of thin air; it came from people. If the Black Death had never happened, there is every reason to think that the modern world would have arrived centuries earlier.

A few challenges for Clark:

1. You think one important reason why food and energy grew cheaper in the modern era is that “Only a small fraction of the world grew rapidly.” But if you look at your own graph, the downward trend continues long after economic growth spread to most of the rest of the world.

2. “The supply of new lands is largely exhausted.” This is factually mistaken. In the United States alone, only about 20% of available land is used for growing crops.[1] This percentage has been roughly constant since the 1930s—not because no other land suitable for farming exists, but because conversion of forests to farmland has been roughly balanced by conversion of farmland to forests.

3. Negative externalities of fertility? Even in a Malthusian world, population is not analogous to air pollution. Suppose we literally lived in a zero-sum world. As long as parents are financially responsible for their children, any negative effect of population on living standards is internal to the family. As Landsburg explains:

When people think about overcrowding or overpopulation, they typically imagine that if, for example, I had not been born, everyone else would have a slightly bigger share of the pie. The truth is that if I had not been born, both of my sisters would have substantially bigger shares of the pie and everybody else’s share would be pretty much the same as it is now.[2]

In other words, the negative externalities, if any, are intra-family. If parents didn’t care about their already existing children, or if children didn’t value siblings, there might still be a problem. But parents do care about their already existing children, and at least many children value having siblings. So it’s unclear whether a problem even exists.

4. Are you actually willing to bet that global real per-capita GDP will be lower in 2020 than it is today? How about 2030? 2050? If you’re willing, let’s hammer out a deal. If you’re not, it looks like I’m not the only one who finds the last two centuries a more reliable guide to the future than the preceding two hundred millennia.


[1]See H. Thomas Frey, “Trends in Land Use in the United States.” In Julian Simon, ed. 1995. The State of Humanity. Cambridge: Blackwell, pp.434-411.

[2]See Steven Landsburg. 1997. Fair Play. New York: Free Press, p.150.

Also from this issue

Lead Essay

  • Bryan Caplan argues that declining world populations aren’t such a good thing after all. While we may have dodged the “population bomb” predicted in the 1970s, the world still benefits from more suppliers — and demanders — of new goods and services. Friends of scientific and cultural advancement should want more people around. All of which leads him to a question: Are there ways to incentivize population growth without sacrificing individual liberty? Caplan suggests several methods, including open immigration, tax incentives for children — and the direct, ultimately private argument that having more kids is more fun than most people realize.

Response Essays

  • Gregory Clark argues that, while Caplan may more or less accurately describe the history of economic development, mineral and other reserves in the West have been significantly depleted. What holds true today will not hold true indefinitely regarding food, energy, and basic mineral commodities. The balance between population growth and resources only recently tipped toward abundance, and it will likely tilt in the other direction soon.

    Clark agrees, however, with Caplan’s suggestion that on the margin, middle-class families stand little to lose and much to gain by having more children; cultural assumptions in the West likely overestimate the importance of nurture, and as a result, middle-class Americans probably do overinvest in their children.

  • Matthew Connelly reviews the history of pro- and anti-natalist policies around the world. He finds them both full of coercion, perverse incentives, misogyny, and — if states try hard enough — atrocity. Population trends, however, are very stubborn, and the payoff to such policies is low. In his words, “economists do not know where babies come from.” Not, anyway, such that they can motivate people without destroying their autonomy. If libertarians are recruited to the pro-natalist side, as Caplan urges, their enlisting could come at the price of individual liberty itself.

  • Betsey Stevenson agrees that parents are often generally less happy than otherwise similarly situated nonparents. But she casts doubt on the theory that excessive parental worry is the source of the unhappiness. The most worrying parents, those who spend the most time on childcare, are also the ones who report relatively higher levels of happiness. There is, moreover, more to life than self-reported happiness, and parents may very well have other desires and values than just this one. Neither self-reported happiness nor economic utility are all that there is to our various ideas of the good life. We still need to learn more about why parents describe themselves as less happy before we can prescribe more children and less worrying as the remedy.