Friday, February 27, 2009

Hans Rosling on Population Growth

I. Peak Population

Whenever you get a chance to watch a speech by Hans Rosling, take it. Last month he posted a video discussing the peak of population growth, and it's very interesting.

Rosling has spent most of his life working on health and development issues, currently he is closely involved with a project to help individuals around the world access and manipulate demographic data, at The site has some interesting ways of building graphs that allow you to see a large number of variables at play at once while still understanding what's going on. I like to imagine this makes Rosling the digital age's William Playfair (you know, the Scot who invented the line graph, the bar chart and the pie chart).

Much of Rosling's work (as a doctor, statistician, and public speaker) emphasizes ways to save children in the poorer regions of the world. Similar work caused Paul Ehrlich to raise a moral dilemma several decades ago in "The Population Bomb":

Treating only the symptoms of cancer may make the victim more comfortable at first, but eventually he dies - often horribly. A similar fate awaits a world with a population explosion if only the symptoms are treated. We must shift our efforts from treatment of the symptoms to the cutting out of the cancer.
In other words, if a high human population damages the environment, and leads to greater poverty, then isn't it misguided and dangerous for Hans Rosling to focus on decreasing child mortality in the developing world?

Rosling provides a response in last month's video which cuts right to the data. He provides interesting trivia and projections along the way.

Many who worry about overpopulation, including Ehrlich, rely on a Malthusian picture of population trends. Unchecked, they believe, birth rates will be high, and populations will grow until famine, plague or some mass extinction event pushes it back. The prevailing respect for Malthus is odd, because when Malthus applied his theory, he predicted that population growth would outstrip food supply in the mid-19th century. (It did not.) Neo-malthusians like Paul Ehrlich subsequently predicted mass famines in the 1970s. So why are Malthusians so often wrong? For starters, birth rates are not consistently high. Factors like increasing GDP and female literacy (among others) tend to push down population growth by lowering family size, even while longevity increases.

II. Sustainable Population

In the video, Rosling discusses where we can expect population to level off. Will that level of population be sustainable?

In evolutionary theory, "adaptive radiation" is used to describe how a species can aggressively fill out a new niche (in that case, through greater diversification). Even in the biological world, nature abhors a vacuum, a given species will quickly expand to find new boundaries. Over the course of history, mankind has faced some huge population explosions, despite no radical adaptive radiation, nor significant gains in territory. Such explosions might be worrisome at first. But if you look back through history, these population spurts often followed agricultural revolutions. It's not that we became more aggressive in breeding, but that we became more efficient at using the limited resources of this planet to sustain more people.

Of course global population will be sustainable once it levels out, because living well under sustainable levels is one factor which drives population growth, and also because the singularity is nigh.

This hits on a concept that I learned from the classic Sim City 2000: Sustainability is determined not by nature, but by technology. Or, the plough was just the first iteration of the arcology.

III. Further Consideration

* Emily Oster discusses how longevity can interact with other systemic social problems, like AIDS and development.

* Birth rates and longevity can be folded into median age, which may be a useful demographic indicator. The US has a median age around 36 years, while almost all of Sub-Saharan Africa has a median age between 14 and 20. We cannot expect Africa to follow a "build infrastructure, then profit!" path to development like the US or Western Europe. Most of the population in Africa is either too young to help build any infrastructure, or cannot expect to enjoy it very long. Increasing health outcomes is an accessible, meaningful, and perhaps obvious first step.

* You can make your own GapMinder graphs through Google Spreadsheets.