# **1. Introduction**

The intergenerational transmission of human capital, and education in particular, is frequently examined through a nature versus nurture lens. We can observe that educated parents tend to have educated children, but it is not clear if this is due to common genetic traits passed from one generation to the next or to the ability of educated parents to provide a better learning environment for their children. The debate has crucial policy implications, since an environmental, rather than a purely genetic, relationship between parental and children’s education would point to positive externalities attached to human capital investments.

Two recent papers by Behrman and Rosenzweig (2002) and Plug (2004) have revitalized this discussion by developing approaches to disentangle the nature and the nurture components of the intergenerational transmission of human capital. Their results suggest that, after isolating the genetic component, there was no environmental effect of mothers’ schooling on children’s education. This paper challenges their conclusions.

Three types of strategies have been used to separate nature and nurture components in the parent-child transmission of education. The first, pioneered by Taubman (1976), compares, as parents, genetically comparable twins with different schooling levels. This method is also used by Behrman and Rosenzweig (2002)<sup>1</sup> : using the twin-method, they find that a mother’s education has a “marginally negative, rather than a significantly positive” effect on their children’s schooling attainment.

The second method is instrumental variables: an exogenous variation in the schooling levels of the parents is used to identify the causal (environmental) effect of parents’ schooling on children’s education. Oreopoulos, Page, and Huff Stevens (2003) exploited historical changes in compulsory schooling laws in the United States and find a positive effect: parental education decreases the probability of grade repetition and drop-out. Chevalier (2004) using a similar approach in the United Kingdom also finds a positive effect of parental schooling on their children’s education. But Black, Devereux, and Salvanes (2003) use reforms of the education system in Norway in the 1960s as an instrument and find no significant positive relationship between parental education and children’s schooling, except in the mother-son relationship.

Comparing adoptive children with biological children is the third strategy. By looking at the outcome of adopted children, genetic effects will disappear leaving only the environmental effect. Sacerdote (2002) uses a British sample of adoptees and finds a positive and significant relationship of parental education on the education outcomes of their children. Björklund and Richardson (2001) find no significant effect among foreign-born adoptees in Sweden. Plug (2004) analyzes outcomes for adoptees from Wisconsin and reports that, when both parents’ education is included in the regression, only the father’s coefficient remains significantly positive, while the mother’s loses its significance. Björklund, Lindahl, and Plug (2004), using data from Sweden, confirm the validity of the adoption strategy and find that

> 1 Notice that Antonovics and Goldberger (2003) question the robustness of their results.

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