“A gene for aggression lands you in prison if you are from the ghetto, but in the board room if you are manor born.” Conley 2011
“Flamingos everywhere are famous for their beautiful pink color. [But] if fl amin- gos do not have access to their usual diet [of shrimp and plankton] for any reason,
they are white, not pink. Their color is entirely dependent on the environmental infl uence of diet. On the other hand, the fl amingo’s ability to turn pink with diet
is entirely dependent on their genes. You could feed seagulls forever on the same diet and they would never turn pink. It would make no sense to say the fl amingos’
color was 50 percent due to genes and 50 percent due to diet. The color is due to the joint action of genes and environment.” Rutter 2006
“The nature versus nurture distinction, although traditional, is obsolete. Genes and environments cannot be meaningfully parsed by traditional linear models that
assign unique variances to each component.” Heckman 2007
I. Introduction
It is well established that family income is an important predictor of educational performance Coleman 1966; Reardon 2011; Björklund and Salvanes
2011; Dahl and Lochner 2012. Education, in turn, is widely seen as a central mecha- nism underlying the intergenerational transmission of economic status Black and
Devereux 2010. Together, these two relationships imply that any factors that affect the link between family income and education will also play an important role in
determining socioeconomic mobility. Conforming to the classic nature versus nurture dichotomy, it is common for researchers to broadly classify such factors into genetic
and environmental components, and economists studying intergenerational mobility and human capital development have long been interested in the relative importance
of genes and environments in determining economic outcomes. See Taubman 1976; Behrman and Taubman 1989; Plug and Vijverberg 2003; Black, Devereux, and Sal-
vanes 2005; and Sacerdote 2007, among many others.
However, modern fi ndings from molecular genetics suggest that this traditional dichotomous approach is often inappropriate, and that interactions between nature
and nurture may be of substantial importance. Rather than any given outcome be- ing neatly divisible into portions attributable to genes and environments, the partial
effect of a particular environmental factor often depends on an individual’s genetic endowment and vice versa. While the possible importance of such interactive effects
have been acknowledged and discussed by economists Heckman 2007; Lundborg and Stenberg 2010; Beauchamp et al. 2011; Benjamin et al. 2012, it remains largely
unknown whether gene- environment interactions play a signifi cant role in shaping basic economic relationships, such as the effect of income on education.
The present paper seeks to begin fi lling this gap in the literature. Using a large national data set that recently collected genetic marker data for its respondents, I in-
vestigate whether the relationship between childhood income and educational attain- ment varies across groups of students with differing versions of the gene monoamine
oxidase A MAOA, which affects the chaperoning and breaking down of neurotrans- mitters such as dopamine and serotonin. The core fi nding is that interactions between
nature and nurture in this area appear to be large. For children with one variant of MAOA, I fi nd that increases in household income have the expected positive associa-
tion with college enrollment, college graduation, and total years of schooling com- pleted. For children with another MAOA variant, who comprise over half of the popu-
lation, I fi nd that there is a much weaker association between economic background and educational attainment. These results hold when the genetic component of the
interactive effects are identifi ed using MAOA variation across full biological siblings, which is determined entirely by chance at the time of conception.
The paper proceeds in fi ve additional sections. Section II lays out a simple theoreti- cal framework and briefl y reviews existing work in this area. Section III describes the
data. Section IV presents the main sets of results. Section V considers several addi- tional issues and the mechanisms underlying the main results. Section VI concludes
by discussing several of the study’s limitations and suggesting directions for future research in this area.
II. Theoretical Framework and Existing Literature
