When I was younger I was very concerned with overpopulation. Today I am not very concerned. When I was younger I read books such as Paul Ehrlich’s The Population Explosion, and Garrett Harden’s The Ostrich Factor: Our Population Myopia. It is because I read these books and internalized their lessons that I am not very concerned. You shall judge a prophet by the veracity of his visions, and the predictions of these books have not come to pass in our time. That is also the conclusion of a piece in The New York Times, The Unrealized Horrors of Population Explosion. In it the reporter observes just how much Paul Ehrlich got wrong, and, also exposes just how unrepentant he is. It strikes many, including myself, that his belief in his theory, his model, is far more robust than his adherence to the philosophy that one must update one’s expectations with new data. We are all familiar with the fact that evaluated over the past ~10,000 years the human population has exploded. But, over the past 50 years the growth has been far less explosive in relative terms. When Paul Ehrlich wrote his original book, The Population Bomb, in the late 1960s the global fertility rate was ~5. Today it is close to ~2.5. When I was born in Bangladesh the fertility rate was close to 7. Today it is close to 2.

The model which Ehrlich and many biologists are enamored of is that of carrying capacity, and the logistic growth curve. It is known to all biologists, and for those in fields such as ecology it permeates their understanding of the phenomena which define our world. In short, density dependent dynamics are such as that over time species reach a carrying capacity, where their numbers are held in “check” by exogenous and endogenous forces. The exogenous being resource depletion, and the endogenous being competition within the species. These are “iron laws” of nature, and it is no surprise that the logistic growth model arose in response to the verbal arguments of Thomas Malthus. Paul Ehrlich, and many of his fellow travelers in the 1970s, were basically neo-Malthusians, and Malthusian thinking is only the formalization and explication of ideas which are as old as humanity itself. Hunter-gatherers engage in birth-spacing and infanticide because of considerations of finite resources. The city-states of ancient Greece practiced anti-natalism and encouraged migration because of resource constraints.

So where did Ehrlich go wrong? Julian Simon, Ehrlich’s nemesis, would say that his model went wrong when it viewed humans as a stress upon finite resources. Rather, humans were the ultimate resource. My friend Ramez Naam wrote a book, The Infinite Resource: The Power of Ideas on a Finite Planet, which outlines a major piece of the puzzle: humans are innovators, and those innovations increase productivity beyond imagining. Without nitrogen based fertilizer there is almost no way that we’d be able to support the population we have today, to give one example. Economists have attempted to formalize this process of growth through innovation (see Knowledge and the Wealth of Nations).

But there’s another element which is often neglected. Humans seem to reduce their fertility of their own will. That is, the demographic transition. Classical economic and ecological theory would predict that as humans produce more resources, they would produce more offspring. Times of plenty result in plenty of descendants. But what happened in nations like England in the 19th century was that gains in economic production correlated with declines in fertility. Naturally the gains were not swallowed by increased numbers. Rather, each human began to consume more and more, as the size of the pie exploded far faster than the number of humans. We live in a world of resource surplus, as the Malthusian trap was torn apart, and the gap between production and population kept growing.

Which comes to the point of this post: those who dismiss the population doomsayers need to be cautious of their own hubris. First, most of the gains in global decline in poverty has been driven by economic growth in China. And, that economic growth has partially been driven by a demographic dividend derived from the favorable dependency ratio of the last generation. It has been reported that Deng Xiaoping was convinced the wisdom of the “one-child policy” after observing that the “Asian Dragon” economies all saw benefits from reduced population growth. And it has to be remembered that this policy is coercive in exactly the manner that Paul Ehrlich had recommended.

But that’s a specific, and tendentious, objection. I say tendentious because China was already going into demographic transition, and East Asian nations which did not enact coercive population control also have very low fertility. But it seems plausible that the policy and the coercion had a major effect on the margin. The fertility would have been higher, and the demographic transition less sharp, without the policy. Since China is a nation of over one billion even marginal effects are very important. The second issue is that this is specific and somewhat narrow focused. The big picture is more important.

Paul Ehrlich himself seems to employ the classic dodge that his predictions will come to pass…you just have to wait long enough. This is a laughable response, even if on some level it is logically coherent. If you wait long enough everything you predict will come to pass. Your credibility stands and falls on whether you can predict it with some level of timely accuracy. It seems that today Ehrlich is resting his case on the fact that estimates always are bracketed by confidence intervals, but if you read his earlier work you’d not get a sense of this at all. What gives? Either he was very confident in the past, and now has simply moved goal posts, or, his writings are a mix of science and ideological polemic. I suspect the truth is a mix of both. But if you talk enough sometimes you’ll land on the truth like a dart on a bullseye.

If you have been reading me for a while you know that one of my favorite books of all time is The Fall of Rome: And the End of Civilization by Bryan Ward-Perkins. The author is an archaeologist, and he reviews the material record, and concludes that contrary to the revisionists and exponents of “Late Antiquity,” a great civilization did fall and decline in the 4th and 5th centuries. Ward-Perkins also emphasizes the Romans of that period did not truly see the great rupture coming. The end of antiquity was a surprise to them, for their world was an eternal one. The Pax Romana had lasted centuries. True, there were interruptions in the calm, such as the Crisis of the Third Century, but they had passed. Though obviously the Roman peace did not engender an affluent consumer society, Ward-Perkins notes that the industrial production in domains such as Britain in the 4th century left evidence in the form of pollution in alluvial deposits which were not matched again until the 18th century!

Focusing upon models such as that of a carrying capacity results in the idea of iron laws which proceed in a deterministic fashion. Neglecting the protean capacity for human innovation, the ability to transform the very parameters of the model itself, is a recipe for looking foolish. But embedded within Paul Ehrlich’s denial of the facts is the deep intuition that social chaos and collapse can come upon us when we’re least expecting it. Human ingenuity is hard to predict, but, it is inevitable. But so are panics and irrational excesses. Innovation and human ingenuity exists in a social context, and that social context may be more easily perturbed than we would like to think. Rather than a clean elegant deterministic model, we need to keep in mind the non-linearities of social processes. The human spirit is the source of our salvation. But it may also be the root of the demons which damn us.