Surnames and a Theory of Social Mobility - University of Chicago ...

Some recent studies of the outcomes for adopted children in the USA and
Sweden, for example, suggest that the characteristics of the adoptive parents has
modest influence on outcomes such as earnings or educational attainment compared
to those of the biological parents. Bjorklund et al., 2007, find that the education of
the biological parents is about twice as influential as that of adoptive parents in
predicting years of education for children. This accords with the adoption study of
Plug and Vijverberg, 2003, which concludes that comparing adopted to biological
children, genetics explains 60-100 of educational outcomes, with some of the
uncertainty here being because we do not know the degree to which birth and
adoptive families are correlated in socio-economic status. Bruce Sacerdote, is able to
exclude such confounding effects, and compare outcomes for Korean adoptees in
the US randomly assigned to families with greater or lesser educational and
economic resources (Sacerdote, 2007). The adoptive families did not include those
at the lower end of the income distribution. US Law required the adoptive families
to be earning at least 125 percent of the poverty level. But the adoptive families
included those across a wide range of income and education.
Figure 15 shows the average family income of adoptees as a function of the
income of the parents at the time of adoption. There is no connection. Absent a
genetic connection between parent and child high income parents are unable to
transmit any income advantage to their children. For non-adoptive children parental
income was positively predictive of child income. But this must be mainly because
of genetic connections between parents and children.
For education there is evidence in the Sacerdote study that parents can have
some effect independent of genetics. Adoptees with adoptive mothers having very
low levels of schooling do show fewer years of school completed, as we see in figure
16. But this effect only exists for mothers at the lower end of the education
distribution. Once we get to mothers with 15 or more years of schooling, which
would include even some without Bachelor’s Degrees, there is no further effect of
more maternal education on adoptive child outcomes.
Overall in the Sacerdote study genetics explained three times as much (or more)
of the variance in years of education, college graduation, and income, as did shared
family environment. The decomposition of variance, however, in all these studies
measures only the additive contribution of genes, and not their contribution through