Chapter 12raised apart from their biological parents, their well- being is
still influenced by that of their biological parents.^3
At the same time, experience is also incredibly important.
Adopted children’s well- being also reflects the well- being of
their adoptive parents, with whom they share no genes at
all. What is more, how they turn out is not just the result of
genes and experience added up. Instead it depends on the
interaction of the genes with experience.^4 For example, ad-
opted children who grow up in a disturbed home are more
likely than other children to become mentally ill, but the
effect of their experience is augmented if their biological
parents were also mentally ill.^5 Similarly, adopted children
who grow up in a criminal home are more likely to become
criminals, but the effect of their experience is augmented if
their biological parents were also criminal.^6 And this mech-
anism is beginning to be understood through the science
of epigenetics that explains how (for example by methyla-
tion) the “expression” of a gene can be silenced as a result of
a person’s experience.^7 Such gene- experience interaction is
pervasive in human life.
The effect of genes can sometimes now be traced to the
operation of particular, specific genes. In a few cases it has
been possible to identify within the DNA genome spe-
cific genes that contribute to well- being.^8 But the number
of genes identified so far is only around three, and they
account for only 1% of the variance of well- being. So, in
studying what causes well- being over the life course, we can-
not simply insert the relevant genes in our array of deter-
minants.
But we should be appropriately humble about what we
can do. For example, suppose we can show that, if your