 9. Behavioral Genetics and Personality  225
Evidence of genetic influence on envi -
ronmental measures has been documented 
using a variety of assessment approaches 
(Kendler & Baker, 2007), including self- 
reports and observational measures of the 
family environments of infants (Braungart, 
Fulker, & Plomin, 1992), children (Rende, 
Slomkowski, Stocker, Fulker, & Plomin, 
1992), and adolescents (O’Connor, Hether -
ington, Reiss, & Plomin, 1995). Moreover, 
identical twins reared together, as well as 
those reared in different families, generally 
report more similar family experiences than 
do fraternal twins (Hur & Bouchard, 1995; 
Plomin, McClearn, Pedersen, Nesselroade, 
& Bergeman, 1988). The reared-  apart twin 
studies provide particularly strong evidence 
that genes influence the way people elicit, 
react to, and create their individual family 
environments, because twins reared apart in 
these studies were rating their different rear -
ing families that in almost all cases shared 
no genetic relationship. Moreover, as people 
grow up and have children of their own, 
they contribute to their children’s family en -
vironments, and parenting style also shows 
nontrivial genetic influence (Kendler, 1996; 
Losoya, Callor, Rowe, & Goldsmith, 1997; 
Perusse, Neale, Heath, & Eaves, 1994). 
Importantly, in most families, parents and 
children share genetic influences, suggest -
ing that genetic transmission of personality 
similarity within families may be reinforced 
by the tendency for family members to cre -
ate and respond to environmental circum -
stances similarly.
This is to say that genetic influences on 
personality may drive genetic influences on 
environmental experiences. Krueger, Mar -
kon, and Bouchard (2003) studied this in 
twins reared apart who provided extensive 
data on both their personalities and their 
rearing-  family environments, from percep -
tions of general family climate (characteris -
tics such as warmth and discipline) to physi -
cal facilities available in the family home 
(e.g., books and tools). The twins’ recol -
lections of their rearing environments were 
partly heritable, and genetic influences on 
recalled environments were entirely over -
lapping with genetic influences on person -
ality; this suggests that genes influencing 
personality also incline people to recall and/
or interact with family members in specific ways, so that the way people are nurtured 
is fundamentally influenced by their natures 
(Plomin & Bergeman, 1991). Such overlap -
ping genetic influences on personality and 
environmental measures extend beyond re -
called family environments, to areas such as 
life events (Saudino, Pedersen, Lichtenstein, 
McClearn, & Plomin, 1997) and parent -
ing styles (Chipuer, Plomin, Pedersen, Mc -
Clearn, & Nesselroade, 1993; Losoya et al., 
1997).
Most Environmental Influences on  Personality 
Are Nonshared, but the Meaning of This 
Finding Remains  Elusive
We have presented evidence from both twin 
and adoption studies that shared environ -
mental influences of this kind are relatively 
weak. Plomin and Daniels’s (1987) classic 
paper enumerating reasons why this might be 
the case is now more than 30 years old, but 
the absence of shared environmental influ -
ences continues to baffle theorists attempt -
ing to conceptualize the processes involved 
in personality development. This bafflement 
is partly due to the fact that the associations 
between offspring outcomes and environ -
mental influences such as parental attitudes 
and rearing styles, religious involvement, 
and socioeconomic status continue to be 
robust. It is also because the search for the 
specific nonshared environmental influences 
that act to make siblings growing up in the 
same family so different has been rather dis -
appointing.
Turkheimer and Waldron (2000) docu -
mented the results of this search in a well-
known meta-  analysis. They concluded that 
a broad range of specifically identified non -
shared familial and peer environmental vari -
ables, considered theoretically important, 
accounted for little, if any, of the nonshared 
environmental variance in personality, at 
least as measured to date (cf. Plomin et al., 
2001). As they saw it, this was likely due 
to measurement difficulties and underlying 
stochastic processes that would elude abil -
ity to detect and quantify the processes in -
volved in personality development for some 
time to come.
Harris (1998, 2006) offered an alternative 
account for the absence of shared environ -
mental influences. She argued that parents 