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Was Malthus mistaken?

Next Tuesday, for the first time in history, the world will have six billion inhabitants. It is with a certain sense of shock that I realize the world's population has doubled since I graduated from high school in 1960. The world seemed to me already full of people then, the cities crowded, spreading suburbs and smog everyday topics of conversation. Now I look around me, seeing a much more crowded world, and wonder "How long can this go on?"

Over 150 years ago the British economist Thomas Malthus predicted that human population growth is bound to outrun our ability to feed ourselves. The problem, he pointed out, is that human populations tend to increase geometrically. Eventually, inevitably, there will be too many people to feed, cloth, and house.

Why was Malthus so concerned about geometric growth? Geometric growth is what your money does in the bank, if left undisturbed. Every year a fraction is added to the total. The next year, the total for which the fraction is calculated is that much bigger. At first the money doesn't seem to grow much, but it is growing faster and faster as the total adds up. Eventually, if left undisturbed, the total will be growing very fast indeed. Compound interest, the bankers call it. If the Indians who sold Manhattan for $24 in beads had instead invested the money at 10% compound interest, they would have enough now to buy it all back, buildings and all.

Malthus warned that the human population will grow at compound interest, faster and faster, until something brings it into check.

Next Tuesday the world's population will be growing at a rate of 148 people a minute (247 births minus 99 deaths), and will equal 6 billion people.

How much is a billion? If this page of newspaper were filled with periods (69 dots per line in six 157-line columns) 6 billion of them would take up about 92,000 pages.

What will stop the human population from growing indefinitely, Malthus pointed out, is the finite capacity of the environment to support so many people. Biologists call this limit the "carrying capacity." As a population begins to approach its carrying capacity, resources become limiting, reducing the population's rate of growth. That's what scared Malthus, the slowing down process. He saw mass starvation as the human population grew beyond our ability to feed it.

Malthus didn't anticipate the impact of technological innovation -- who in 1850 could have imagined automobiles, or genetic engineering? The world did not in fact undergo mass starvation as Malthus had predicted, because as the human population grew, so did humanity's ability to feed it. A biologist would say technology has expanded the world's carrying capacity.

We live today in a world supported by continual economic growth. Economists have long ago written Malthus off as some kind of alarmist quack. On September 19 my favorite New York Times reporter Nicholas Wade wrote an article titled "Why Malthus was mistaken." Wade argued that the American population was "clearly not in doubling mode today," and that the "Malthus gospel" was a "consistent fallacy."

Do you see the discontinuity in what Wade is saying? He, and the many economists who largely structure the world we live in, are assuming that the world's carrying capacity can be expanded indefinitely. Any biologist will tell you that this just ain't so. Technology has expanded carrying capacity by borrowing against the future, damaging the environment and consuming resources it cannot replace. Most informed ecologists doubt whether the world can sustain a population of 6 billion, much less the billions of extra people that will be added in the future.

Technology can only delay the day Malthus feared, not repeal the basic laws of biology. We can only hope that as we enter the new millennium, fertility rates will gradually drop. In 1960 the world's population growth rate was about 2 percent. Today it is about 1.3 percent. The danger, unspoken by economists, is that at some point before growth rate falls to zero (that is, before we reach a stable world population size), we will have exceeded the world's carrying capacity. When this happens in animal populations studied by ecologists, population size often falls like a rock. One day there is just enough for everybody, the next, not quite enough for anybody. That was Malthus's warning, the nightmare that haunted him. Next Tuesday is not a date to celebrate, but to ponder.

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