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Grant McDermott

Data. Economics. Environment.

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Poor Thomas Malthus. Has there ever been a more maligned and misunderstood figure in the history of economics?

With depressingly few exceptions, both his critics and supporters seem equally uninterested in discussing what the man actually wrote. Hardly a day goes by without some mocking reference to the Malthusian Doom that never seems to arrive and its progenitor's endless list of imagined shortcomings. For their part, most "modern Malthusians" in the environmental movement are equally ignorant of what the good Rev'rend was trying to get at, despite their appeals to his authority.

To try and illustrate by way of an example, consider this article by Ivo Vegter in South Africa's Daily Maverick. I'm going to ignore the general thrust of the post \(-\) parts of which I agree with \(-\) and focus specifically on what he writes about Malthus:
Malthus’s theory was simple. In fact, “simplistic” would be a better word for it. He postulated (though did not prove) that human population increases geometrically, while resources increase arithmetically. Geometric growth (often called exponential growth) occurs by multiplying a given quantity every year. Arithmetic growth (also known as linear growth) involves merely adding a fixed quantity each year. No matter what, the former will always outpace the latter over time. 

Let Malthus illustrate it himself: “Taking the population of the world at any number, a thousand millions, for instance, the human species would increase in the ratio of 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, &c, and subsistence as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, &c. In two centuries and a quarter, the population would be to the means of subsistence as 512 to 10.” 

Even a non-economist can understand this trivial piece of arithmetic. The problem is that neither postulate – not geometric growth in population nor arithmetic growth in resources – was supported by empirical evidence or economic theory. In fact, since neither has anything to do with reality: asserting them probably qualifies for at least some definitions of the word “mad”.
Okay, there's a lot that needs correcting here... and this despite the fact that Ivo spends a third of his time directly quoting the man! The first thing to note is that “postulates” is the wrong word to describe Malthus’s characterisation of population and resources [read: food] growth rates. Rather, he deduced these growth rates from preceding postulates and observations about the real world. Indeed, Malthus is quite clear about what his actual postulates are: “I think I may fairly make two postulata. First, That food is necessary to the existence of man. Secondly, That the passion between the sexes is necessary and will remain nearly in its present state.

So, we're not off to the best of starts. Still, you could argue that mixing up assumptions and subsequent deductions is perhaps a harmless offence in this case... so long as Ivo gets his basic critique right. Let's look a bit deeper at his specific criticisms then:
The problem is that neither postulate – not geometric growth in population nor arithmetic growth in resources – was supported by empirical evidence or economic theory.
This, particularly with regards to Malthus’ “postulate” on population growth, is quite false. Among other things, Malthus supported his theoretical arguments with empirical evidence from the newly established USA, which had doubled in size every twenty-five years. (Adam Smith had made similar observations in The Wealth of Nations two decades earlier.) The richly-endowed and untapped New World was especially relevant to Malthus, because his entire theoretical argument hinged on how population levels would hypothetically evolve free of natural constraints. Far from claiming this as the expected order of things, Malthus is very clear in his thinking [emphasis added]:
I said that population, when unchecked, increased in a geometrical ratio[...].

Let us examine whether this position be just.

I think it will be allowed, that no state has hitherto existed (at least that we have any account of) where the manners were so pure and simple, and the means of subsistence so abundant, that no check whatever has existed to early marriages; among the lower classes, from a fear of not providing well for their families; or among the higher classes, from a fear of lowering their condition in life. Consequently in no state that we have yet known has the power of population been left to exert itself with perfect freedom.
As a stylized biological assumption, I really don’t see what the problem is. Ivo again misconstrues the matter when he later writes: “Therefore, assuming geometric growth in human populations is a simplistic fallacy.” No, it is a reasonable benchmark upon which we can compare observed population growth rates!

Malthus later provided further empirical justification for his theoretical arguments in his second Essay on the Principle of Population; for instance, citing evidence from his travels in Scandinavia. I mention this not only to show that Malthus didn't simply pull these figures from his nether regions... but because it is important to note that he substantially revised upon his original essay after it was first published. Each time he undertook such a revision, he would address criticism and seek to add further evidence in support his arguments. By the 6th edition of Population, he had pulled together evidence from over 20 different countries and cultures.

If Malthus provided sound reasoning and evidence for his arguments on population growth, then he was undoubtedly on shakier ground with his assertions on food production. In fact, his downfall here was to base his arguments largely on historical observations of agricultural yields... so even then I don’t see how you could argue that there was no appeal to empirical evidence.[*] That's not to say that he didn't try to provide any theoretical underpinnings to his position, as he effectively described agricultural production as being subject to \(-\) what we would today call \(-\) diminishing returns to scale. From his second essay [emphasis added]:
The science of agriculture has been much studied in England and Scotland; and there is still a great portion of uncultivated land in these countries. Let us consider at what rate the produce of this island might be supposed to Increase under circumstances the most favourable to improvement. 

[...]In the next twenty-five years, it is impossible to suppose that the produce could be quadrupled. It would be contrary to all our knowledge of the properties of land. The improvement of the barren parts would be a work of time and labour; and it must be evident to those who have the slightest acquaintance with agricultural subjects that, in proportion as cultivation extended, the additions that could yearly be made to the former average produce must be gradually and regularly diminishing.
Malthus failed to grasp how technological innovation would revolutionize agricultural production, it is true. One could argue that this was at least partially due to the fact that he couldn't foresee how future discoveries of fossil fuels \(-\) oil in particular \(-\) would completely transform the way in which people farmed... from agricultural mechanisation to petroleum-based fertilizers.[**] However, it is abundantly clear that Malthus didn't think up baseless assumptions from which he could then make wild claims about mass starvation and future misery. His much more conservative point was that population increases would be subject to natural checks on food supply.

I'm just a soul whose intentions are gooood

THOUGHT FOR THE DAY: Ivo is not alone in drawing a crude caricature of Thomas Malthus. Indeed, to repeat what I said at the beginning of this post: the man might be the most misrepresented person in the history of economic thought ... which is saying something in of itself. I’m not suggesting that Malthus was correct in his Population Essay(s), because he clearly overlooked the likelihood of tremendous advances in agricultural technology. However, it’s extremely discouraging that such a profound thinker is tied to his “worst” idea, and a cartoon version at that.
[*] A more sophisticated argument might be to criticize Malthus for relying on a form of historicism, as opposed to empirical evidence. This is certainly a better line of attack, although not incontestable given the very broad context of his writings.
[**] In this way, he partially foreshadowed William Stanley Jevons, who actually wrote about energy matters... see here.