Monthly Archives: February 2013

Genetic diversity and economic development

Recently two economists, Quamrul Ashraf and Oded Galor, published an article in a prominent economics journal comparing genetic diversity in various countries with economic development (ungated version here).  They found the following relationship: high and low genetic diversity is associated with low economic performance.  High economic performance is associated with moderate levels of genetic diversity.  Below is the take-home “hump-shaped” graph comparing genetic diversity to per capital income for a slew of countries (lower numbers on the x-axis represent higher genetic diversity).





Ashraf and Galor conclude that this relationship supports the hypothesis that “genetic diversity within a population confers both social costs, in the form of miscoordination and distrust arising from genetic differences across members of society, and social benefits in the form of diversity-driven knowledge accumulation.

Needless to say, this interpretation caused some controversy.  A group of anthropologists (mostly from Harvard) penned a response in Current Anthropology before the original article was even published (ungated version).  Jason Collins, at Evolving Economics, has been covering the fall-out in detail.


Much of the back-and-forth has been about the specific methods employed by Ashraf and Galor.  I am going to leave that to others and instead focus on Ashraf and Galors proposed mechanisms.  For what it is worth, I mostly agree with Andrew Gelman’s take on the other issues.
 

Critique 1: If any finding is consistent with an hypothesis, finding something is not very good support for the hypothesis.

 

Ashraf and Galors’s hypothesis, as quoted above, predicts that genetic diversity should have both a positive and a negative effect on economic productivity. The great thing about this sort of hypothesis is that it can explain any observed pattern in the data.

For example, in the stylized charts below, the top chart reflects the findings of Ashraf and Galor, highlighting the positive and negative effects of genetic diversity creating a “hump-shaped” curve.  The bottom chart reflects the exact opposite findings: a “trough-shaped curve.”  Notice that this curve is also consistent with Ashraf and Galor’s hypothesis – showing regions of “negative effects” and regions of “positive” effects.  Even a flat line would be consistent with their hypothesis (the effects cancel out!).  If any empirical pattern is consistent with an hypothesis, finding a specific empirical pattern that is consistent with the hypothesis is not too surprising.





Critique 2: Genetic Difference Only Matters on (Very) Small Scales

There is a large body of work in evolutionary biology on the scale at which genetic differences should matter in cooperation. The consistent finding is that genetic differences only matter for very close relatives, for animals like humans who have fairly limited number of offspring (unlike social insects), the scale at which genetic differences might matter is something under a dozen individuals.  Any more than that and genetic relatedness is just too diluted to make a difference. 

Countries are much bigger than a dozen individuals. Within a country, people might be more cooperative with their immediate relatives, but any genetic diversity beyond that shouldn’t matter.
  
When they hypothesize that genetic differences cause “miscoordination and distrust arising from genetic differences across members of society” this sounds a lot like kin recognition.  Basically, individuals act differently towards others based on observed genetic similarities and differences. In the classic paper by François Rousset and Denis Roze, they find that even under the most ideal conditions, kin recognition only works in extremely small groups [summary here].

 

Critique 3: Genetic Diversity Cannot Explain (much) Cognitive Diversity

Political scientist Scott Page has two books summarizing research into diversity from a variety of academic disciplines. One of the books’ key points is that are that the important type of diversity in group decision-making and innovation is “cognitive diversity,”  defined as “differences in how people see, categorize, understand, and go about improving the world.”

For example, economists see and understand the world differently than population geneticists. This implies that a study about population genetics and economics would be better if conducted by a mixed group of economists and population geneticists, than by a group of only economists or a group of only population geneticists (see what I did there).

What are the sources of cognitive diversity? Are they likely to be genetic? The answer is no.  The basic argument is that in any given group there is much more cognitive diversity than genetic diversity. Therefore, genetic diversity cannot explain very much cognitive diversity. Most cognitive diversity seems to result from differences in training and experience.

(Update: After posting this, I saw that Jason Collins posted today on the claimed relationship between genetic diversity and innovation.)

 

Conclusion: Reasons to Be Skeptical

 
I am skeptical of the conclusions of this study for three basic reasons. (1) The hypothesis is consistent with any observed pattern in the data, (2) the hypothesized negative effects of genetic diversity are unlikely to matter on the scale of countries, (3) the hypothesized positive effects of diversity are unlikely to be a result of genetic diversity.