220 II. BIOLOGICAL  FOuNDATIONS
resents, its absence in understanding adult  
personality may not be too surprising. Re -
call that it reflects environmental influences 
that vary among families but make people 
growing up together within families simi -
lar, independent  of genetic endowment. It 
reflects environments working separately 
and independently  from genetic influences 
in a manner that reflects not mean level but 
population-  level variance (though theories 
posit primarily mean-level shared family in -
fluences). If environments and DNA work 
together to produce personality in more 
transactional  (interactive and correlational) 
manners, their influences tend to appear 
in the genetic or nonshared environmental 
components of variation in personality (Pur -
cell, 2002), under the models used to gener -
ate these classic observations.
These observations regarding genetic and 
environmental influences are not limited 
to self-  reports, and also extend to observer 
reports. Riemann, Angleitner, and Strelau 
(1997) studied self- and peer ratings of the 
Big Five simultaneously, and found that self- 
and peer ratings showed broadly similar lev -
els of genetic influence. In addition, much 
of the reliable variation was common to the 
self- and peer ratings, which were positively 
correlated (.55 on average). These observa -
tions are important, because together they 
indicate that neither the behavioral nor the 
genetic signals picked up by specific reports 
of personality are unique to the reporter. 
Personality traits are not simply in the minds 
of specific reporters, but rather reflect both 
heritable and environmentally influenced 
consistencies that can be detected from mul -
tiple vantage points (Kandler, Riemann, Spi -
nath, & Angleitner, 2010; Malanchini et al., 
2019).
These consistencies also extend beyond 
reports of personality, to direct behavioral 
observations. This was a critical extension, 
because the vast majority of our understand -
ing of the genetics of personality is based 
solely on adult self-  reports of personality 
traits (Brody, 1993). The work of Borkenau, 
Riemann, Angleitner, and Spinath (2001) in 
the German Observational Study of Adult 
Twins (GOSAT) filled this critical gap in 
the literature. Three hundred pairs of adult 
twins from throughout Germany were vid -
eotaped while engaging in 15 distinct tasks, and judges independently rated the twins’ 
personalities from these videotapes, using 
bipolar rating scales corresponding with the 
Big Five. Assessed in this manner and mod -
eled as latent phenotypes, the Big Five do -
mains all showed notable heritability, with 
a median value of 41%. Interestingly, and 
in contrast to most self-  report findings, the 
video-based observational assessments in 
GOSAT also showed nontrivial shared envi -
ronmental influences on average, with a me -
dian value across the Big Five of 26%. An -
other report from the GOSAT group focused 
on genetic and environmental contributions 
to observers’ personality ratings aggregated 
across the 15 tasks, as well as the extent to 
which there were residual genetic influences 
on task-  specific ratings (Borkenau, Rie -
mann, Spinath, & Angleitner, 2006). The 
group reported that cross-  situational genetic 
influences tended to be stronger than task- 
specific genetic influences, albeit both cross- 
situational and task-  specific genetic influ -
ences were observed.
Taken together, these reports from the 
GOSAT group were important, because 
they extended the study of genetic and en -
vironmental influences on personality be -
yond its traditional focus on self-  reports. 
Evidence for genetic influences on personal -
ity in adults is not limited to self-  reports but 
extends also to observations (Borkenau et 
al., 2001). Moreover, cross-  situational con -
sistency is not the only place where genetic 
influences have been observed; heritable in -
fluences have also been observed on individ -
ual behavioral differences in specific tasks 
(Borkenau et al., 2006).
Finally, nonshared environmental influ -
ences are as large as, if not larger than, ge -
netic influences. Although these nonshared 
environmental influences are not trivial in 
the aggregate, they have been hard to link 
with specific psychological constructs (Plo -
min, Asbury, & Dunn, 2001; Turkheimer 
& Waldron, 2000). As with the absence of 
shared environmental effects, the presence— 
but frustrating anonymity—  of nonshared 
environmental effects may be profitably ad -
dressed by pursuing a more transactional 
conception of genes and environments. We 
return to and elaborate on ways to articulate 
gene–  environment transactions throughout 
this chapter, because we consider this to be 