 9. Behavioral Genetics and Personality  229
life satisfaction were greater at lower levels 
of financial standing. Money appeared to 
buffer the impact of random environmental 
shocks, thus allowing clearer expression of 
individuals’ genetically influenced happiness 
set points (Lykken, 1999). We (Krueger, 
South, Johnson, & Iacono, 2008) observed 
that adolescents’ perceptions of their rela -
tionship with their parents impacted the 
relative importance of genetic and environ -
mental influences on positive and negative 
emotionality. For example, higher levels of 
perceived parental regard were associated 
with greater genetic influences on positive 
emotionality. Moderating influences on per -
sonality are not universal, however; Kendler, 
Aggen, Jacobson, and Neale (2003) found 
no evidence that family dysfunction mod -
erates genetic and environmental effects on 
neuroticism. Similarly, South, Krueger, El -
kins, Iacono, and McGue (2016) observed 
that influence of romantic relationship satis -
faction on individual personality traits var -
ied in magnitude.
These types of moderating influences 
might also work in the opposite direction, 
with personality constructs acting to moder -
ate genetic and environmental influences on 
various outcomes. It is tempting to charac -
terize the phenomena described as “gene × 
environment interaction,” or genetic control 
of sensitivity to different environments, but 
this rubric is conceptually problematic be -
cause, as described earlier, various aspects 
of “the environment” also show genetic in -
fluences; that is, the ways in which people 
perceive environments are also affected by 
genetic influences on how people interpret 
the external world. “The environment” may 
sometimes be better conceived as people’s 
psychological experience of the world rather 
than some putatively objective aspect of the 
world outside the person. Moreover, mod -
eration of genetic and environmental influ -
ences could reflect gene–  environment cor -
relation, in which genetic factors influence 
people’s choices of environmental niches. In 
addition, environmental circumstances such 
as social policies can result in correlations 
between genotypes and particular environ -
mental niches.
Along these lines, we (Johnson & Krueger, 
2005) found that subjective sense of control 
moderates genetic and environmental influ -
ences on health in a manner similar to the more putatively objective environment pro -
vided by the person’s income. Greater sense 
of control and higher income both acted 
to suppress genetic influences on physical 
health. South, Krueger, Johnson, and Iacono, 
(2008) observed that high levels of positive 
emotionality are associated with greater ge -
netic influences on parental regard. The fact 
that high levels of parental regard are also 
associated with greater genetic influences on 
positive emotionality in that study suggests 
a bidirectional feedback loop whereby ado -
lescents with positive emotional dispositions 
elicit parental regard, a situation that fosters 
enhanced expression of genetic influences 
on positive emotionality. Similar to Boom -
sma and colleagues’ (1999) observations re -
garding the impact of a religious upbringing 
on disinhibition, Timberlake and colleagues 
(2006) observed that self-rated religiousness 
reduced the impact of genetic influences on 
initiation of smoking.
In summary, there are now quite a few ex -
amples in the literature of how family and 
other circumstances moderate genetic and 
environmental influences on personality. It 
seems the family does indeed matter in un -
derstanding the origins of personality, but it 
does so through enhancing or dampening ge -
netic endowments; that is, rather than acting 
directly to make children in the same family 
more similar than they would be by virtue 
of the extent to which they share genes (i.e., 
through shared environmental main effects), 
families influence the manner and degree in 
which genetic influences are expressed.
Personality Is Linked to  Outcomes 
through  Correlational 
and Interactive  Processes
When we use traditional methods to esti -
mate genetic and environmental sources of 
variance, we assume that there are no gene– 
environment interactions or correlations 
that would act to create differing degrees of 
genetic and environmental influences within 
different subgroups of the population, of the 
kind that the new methods described above 
allow us to estimate. Gene–  environment 
interactions (G × E) occur when genetic 
expression is moderated by environmental 
circumstances. A simple example is suntan. 
Our genes express darker skin color when we 
spend more time in the sun. As a personality- 