Is genetic distance a plausible measure of cultural distance?
James D. Fearon
Department of Political Science
Stanford University
(Notes on some research in progress; not for citation or circulation)
June 4, 2006
1. Introduction
In a very interesting and potentially controversial paper, Enrico Spolaore and Romain Wacziarg
(2006) show that the difference between two countries’ per capita income levels is associated
with a measure of the genetic distance between their populations. The estimated coefficient is
substantively significant (the standardized beta is usually around .20), and is robust to the inclusion
of a large number of controls, including various measures of geographic distance.
Spolaore andWacziarg (SW) interpret the association primarily as follows: Genetic distance
between populations is a measure of cultural barriers to exchange and interaction between them.
Thus, if productivity enhancing technological innovations occur randomly across populations, they
will tend to spread more quickly to culturally more similar populations, giving rise to a correlation
between income differences and genetic differences.
Why should genetic distance – measured by the probability that randomly sampled individuals
from two populations have different alleles in certain gene locations – be a valid measure for
cultural barriers to transmission of knowledge and know-how? SW think of both culture and DNA
as “vertically transmitted characteristics” that are passed from parents to children. They “interpret
the effect of genetic distance on income differences as evidence of an important role for vertically
transmitted characteristics, reflecting divergent historical paths of different populations over the
long run” (p. 4).
The genetic distance measure are, in effect, measures of the time since two populations diverged,
or separated. For “recently” separated populations, these times may be on the order of a 1000 years.
The idea would seem to be that the longer two populations have been separated,the more time there
has been for each to develop distinct cultural or other vertically transmitted characteristics that would
pose barriers to the spread of technology in modern times (say, the last 200 years). Cavalli-Sforza,
Menozzi and Piazza (1994) show that there is a rather close correspondence between language trees
representing the genealogy of language separations with their trees mapping genetic separations........