Sunday, May 16, 2010

Malthusians Vs Cornucopians

The arguments around overpopulation and sustainable living tend to fall into two camps - the Malthusians and the Cornucopians. Each camp is sure it is right, and derides the other. The problem is that the arguments of both camps are flawed, and thus we are no clearer in understanding this very important topic.

The Malthusians get their name from Reverend Thomas Robert Malthus, who wrote the first edition of An Essay On The Principle Of Population in 1798 and the (final) sixth edition in 1826. Malthusians include Paul R. Ehrlich who wrote The Population Bomb (1968) and The Population Explosion (1990) and predicted widespread famines by the year 2000. A contemporary Malthusian is Professor Albert Bartlett who has lectured on population doubling over 1500 times and declares the human inability to understand the exponential function as our greatest failing.

Cornucopians get their name from ancient Greek mythology in reference to the horn of plenty or cornucopia. Another name for the Cornucopians is anti-Malthusians. Their most famous proponent, and nemesis of Paul R. Ehrlich, was economist Julian Simon. A contemporary Cornucopian is Ronald Bailey of Reason magazine.

The Malthusian argument goes like this. Population grows exponentially and so will inevitably outstrip any resource base, leading to mass famine. The Malthusian use of the concept of exponential growth is nearly always a constant rate of growth from which we derive - via the Rule Of 70 - the population doubling period. Hence, a growth rate of 1% results in a doubling period of 70 years whereas a growth rate of 2% results in a doubling period of 35 years. It sounds simple enough, so what's the problem?

The problem is that no population grows at a constant rate and hence it is claimed that no population grows exponentially. This the Cornucopians point out with glee, thus concluding that the Malthusians are wrong and that we have nothing to worry about. After all, it is claimed, humans are infinitely inventive and the more people we have then the more potential there is for human inventiveness. Technology, fuelled by human inventiveness, will surely find a way to feed humanity forever (or at least for the next several million years). So runs the Cornucopian argument.

So who is right? Should we worry about population growth, overpopulation and limits to growth?

Well, the Cornucopians are right to point out that populations do not grow via constant rate exponential growth. They never have, and they never will. However, given that populations grow via variable rates of growth, the question is whether or not such growth is comparable in power to constant rate exponential growth.

The answer is that...yes, variable rate population growth is comparable to constant rate exponential growth. This is clearly illustrated in my article The Scales of 70 and then proven in detail in the accompanying article The Scales Of e.

A classic example is the population doubling of our global population of 3 billion in 1960 to 6 billion in 1999. That's just 39 years, and didn't require any constant rate of exponential growth. Interestingly enough, the growth rates were roughly between 1% and 2% for those 39 years. Remember, classic exponential growth at a constant rate can be roughly modelled using the Rule of 70, which would have predicted doubling periods of 70 years for a 1% growth rate and 35 years for a 2% growth rate. So the actual population doubling period of 39 years is nicely bracketed by the predicted exponential growth doubling periods of 70 and 35 years.

Hence although the Malthusians are presented a flawed version of their argument they are essentially right. Variable rate population growth can outstrip any resource base in time frames that are exactly comparable to constant rate exponential growth.

Thanks for reading,


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