Natural selection and the collapse of economic growth

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**This is a cross-post from my blog Evolving Economics

In my last post, I discussed Oded Galor and Omer Moav’s paper Natural Selection and the Origin of Economic Growth. As I noted then, my PhD supervisors, Juerg Weber and Boris Baer, and I have written a discussion paper that describes a simulation of the model.

In the discussion paper we consider the entry of people into the population that have a low preference for child quality – i.e. they weight child quantity more highly. Entry could be through migration or mutation. We show that if people with a low enough preference for quality enter the population, their higher fitness in the modern growth state can drive the economy back into Malthusian conditions.

To show this, we simulated a version of the model which had present at a low level in the initial population a genotype with a very low preference for educating their children (I refer to them as the strongly quantity-preferring genotype). This strongly quantity-preferring genotype has a similar fitness to other genotypes that do not educate in the Malthusian state, and declines in prevalence while the quality-preferring genotype increases.

Once the economy takes off into the modern growth state, the strongly quantity-preferring genotype has the highest fitness as it dedicates the lowest proportion of its resources to educating its children. The strongly quantity-preferring genotype increases in prevalence until, eventually, the average level of education plummets, undermining technological progress. The world returns to a Malthusian state, with high population growth eroding the income benefits of all earlier technological progress.

The following chart shows the rate of growth of population, technological progress and income per person. The first 70 to 80 generations look like the base model simulation I described in my earlier post. However, after that point, technological progress plummets to zero. For the next 150 or so generations, population growth is positive, which can occur as per person income is above subsistence. Eventually, population growth drives income down to subsistence levels.

In the next figure, you can see that the strongly quantity-preferring genotype, genotype c, grows from being a negligible part of the population to being over 90 per cent . It is this change in population composition that drives the return to Malthusian conditions (you can also see the small peak in quality-preferring types around generation 48 that kicks off the Industrial Revolution). The strongly quantity-preferring genotypes educate their children far less than the other genotypes, depressing technological progress.

There is no escape from the returned Malthusian conditions. The quality-preferring genotype will have a fitness advantage in this new Malthusian state and will increase in prevalence. Whereas that caused a take-off in economic growth the first time, this time there is no take-off. The strongly quantity-preferring types, which now dominate the population, cannot be induced to educate their children. They simply breed faster to take advantage of any technological progress spurred by the small part of the population that is educating their children.

This result could also be achieved by introducing the strongly quantity-preferring genotype into the simulation at other points in time. If it occurs after the Industrial Revolution, the timing of the return to Malthusian conditions will occur later. However, short of restricting the range of potential quality-quantity preferences, there is no way to avoid the return to Malthusian conditions in this version of model. The strongly quantity-preferring genotypes will always have a fitness advantage when income is above subsistence and their population growth will drive income back down to subsistence levels.

There are, of course, a few possible interpretations of this result. The model or assumptions may be missing an important element (or at the extreme are wrong). Humans may only have quality-quantity preferences in the growth promoting range. Or possibly, modern levels of economic growth are only transient.

7 Comments

  1. I like your plot summary of Idiocracy, but I seem to remember it ending more positively.

  2. Best and most frightening article I have read in some time. (Also very concise. Bravo.)

  3. I made a similar but non-quantitative argument but using the effect of intelligence on child mortality rates.

    http://charltonteaching.blogspot.com/2011/05/child-death-and-demographic-change-and.html

    But both models reach the same conclusion: that modernity is self-destroying, and we are currently en route to a return to zero growth agrarian societies (and the Malthusian trap).

  4. But both models reach the same conclusion: that modernity is self-destroying,

    No, its not. It just has to move on to the next step that consists of transhumanism, radical life extension and space colonization; possibly with eugenics mixed in.

  5. so number of children is due to “genotype”? funny, i thought it was largely dependent on socioecnomoic and cultural factors. but don’t mind me, i’m from a dying genetic branch (my great-grandmother hat seven children, my grandmother had one and i have none — lots of mutations going on there apparently).
    mind you i’m not saying that current trends in differential reproduction are unproblematic. but if your argument hinges on premises this flawed, nobody who knows anything about population will take you seriously.

  6. Twin studies suggest that since the demographic transition, heritability of fertility has been well above zero. Some people respond to the socioeconomic shocks differently to others.

  7. This paper simply illustrates the economists should not be allowed to comment on anything.

    We know economics is wrong, because the debt crash of 2008 exposed all their thinking of the last 30 years as rubbish.

    So sod off back to your den, read some demographic literature and stop applying stupidly simplistic theories to idiotic assumptions to create profoundly over-simplified “models”. It’s crap.

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