Capita

Pop quiz. Suppose you start with a human population of size two, and the population grows at an annual rate of 2%—that's the rate at which a population will double in 35 years. At that rate, it takes 1,128 years for the population to reach 10,000,000,000, which hypothetically we'll call the carrying capacity of Earth. Now suppose that after filling Earth, humans discover a nearby Earth-like planet that also supports 10,000,000,000 people, and further suppose humans innovate the means to transport themselves and their stuff to that planet cheaply, safely, and instantly. How long would it take to fill the new planet to its carrying capacity?

The answer is—duh!—35 years. Filling a second planet is merely another way to double the existing population, and 35 years is the doubling rate. And after filling that new planet, it would take 35 years to fill two more planets, then another 35 years to fill four more planets, another 35 years to fill eight more planets, and so on.

There's a physicist named Albert Bartlett who lectures on overpopulation, and he says inability to understand exponents is humankind's greatest shortcoming. Maybe he overstates his case, but there's a lot of failure going on in people's understanding of what per annum growth is all about, as evidenced by all the talk one hears these days of sustainable growth. There is not and can never be any such thing as sustainable growth, not for as long as the laws of physics resemble anything like what we understand them to be. As an upper-bound example, at our species' present size and with a 2% growth rate, it would take a mere 5,000 years for humans to convert all mass in the observable universe to human flesh. That's about as long as humans have been living in cities.

I pride myself on being able to understand a diversity of arguments, irrespective of whether I agree with their premises, but the argument that humanity has not, is not, and will not continue to be plagued by overpopulation problems is one I don't understand. It's not that I disagree with the premises. Instead, it's that any case that's to be made that overpopulation is not a continual threat for a successful species, including ours, has neither math nor biology on its side.

From the mathematical perspective, the problem is that exponential growth is fast—even if the annual rate is low, such as 2%. In our finite observable universe, all exponential growth must fail eventually.

But some people think this isn't a problem for us modern humans. Isn't our species' rate of growth slowing down? Aren't demographers predicting our species' population to stabilize sometime in the 21st century? Aren't the Malthusian doom-sayers going to be proved wrong?

This idea—that humankind will come to gracefully control its population—isn't the escape from overpopulation it may at first appear to be. And this has to do with biology.

The problem isn't merely that humans, on average, want to reproduce a lot. The scenario in which we're gracefully controlling our numbers hypothetically has that problem solved—presumably through the use of mild voluntary contraceptives, such as television. No, the problem begins specifically after we've stopped growing as a species: Natural selection requires a lot of graceless population control in order to work. Without some forceful culling from it, a gene pool isn't selected for anything, and given enough time without the negative feedbacks of selective pressures to keep it fit for its environment—whatever that may be—a genome will degrade. In short, without a drive to keep growing, a species will eventually find itself ousted by one or more other species. As living things, the point is not that we grow but that we try to grow.

I don't know what will happen in the 21st century or any other future century, but I do know that over the long term there'll be no such thing as graceful population control. Nor will there be sustainable growth. At best there'll be bursts of unsustainable growth followed by longer periods of graceless population control, and the latter will take the same regrettable forms as it has for past generations.

Why are we so afraid of this?