 11. Personality Development across the Life Course 263
ably close to the estimates provided by Fral -
ey and Roberts (2005).
It appears that personality across many 
decades is stable, but the stability is relative -
ly modest. What does this mean? Cognitive 
ability appears to be much more stable over 
similar time spans (Deary, Whiteman, Starr, 
Whalley, & Fox, 2004). In this way, cogni -
tive ability and personality traits are dis -
tinctly different (see also Briley & Tucker- 
Drob, 2014). There is much less stability in 
personality traits over long time spans, in -
dicating that though there is some continu -
ity, there is a preponderance of change over 
multiple decades.
There is another period of the life course 
in which the levels of continuity are quite 
low, that when combined with the findings 
over the entire life course hold some impor -
tance for how we conceptualize personality 
traits. In particular, the levels of continu -
ity from early childhood to adulthood are 
remarkably modest, often hovering around 
.10 when tracked from age 3 to the mid-
20s, for example (Caspi et al., 2003). These 
low correlations are important for inform -
ing the extent to which genetic factors cre -
ated at conception play a conspicuous role 
in personality stability, which is a common 
assumption (Tucker-  Drob & Briley, 2014). If 
the correlation from toddlerhood to adult -
hood is only .10 and the average long, long-
term stability of personality is only .20, 
then other factors must explain the higher 
levels of stability found over shorter periods 
of time, especially across adulthood. In a 
recent revision of the sociogenomic model 
of personality traits (Roberts, 2018), we 
proposed that beyond the stability caused 
by genetic differences found at conception, 
certain epigenetic changes may bring about 
changes in personality (described as pliable 
processes ) that are functionally permanent. 
These factors may explain why adult levels 
of personality remain modestly more stable 
than those from childhood to adulthood. 
Beyond pliable factors, we also proposed 
epigenetic changes that work over longer 
time windows than typical state–trait mod -
els posit, such that changes in personality 
can occur and stay in place for months (if 
not years) before dissipating. Regardless, the 
modest levels of stability in personality traits 
over long time periods call into question the 
importance of genetic factors for personal -ity traits, especially those determined at the 
beginning of life.
How Do Personality Traits Change with  Age?
At the time of the writing of the chapter in 
the previous handbook (Roberts, Wood, & 
Caspi, 2008), the prevailing perspective was 
that personality traits continue to change 
in adulthood, often into old age, and that 
these changes may be quite substantial (e.g., 
Mroczek & Spiro, 2003; Roberts, Walton, 
& Viechtbauer, 2006; Srivastava, John, 
Gosling, & Potter, 2003). Specifically, cross- 
sectional research (comparisons of different- 
age participants at a single time point) has 
shown that middle-  aged individuals tend to 
score higher than young adults on agreeable -
ness, conscientiousness and emotional sta -
bility, and lower on extraversion and open -
ness (Lucas & Donnellan, 2011; Specht, 
Egloff, & Schmukle, 2011; Srivastava et al., 
2003). Moreover, within middle adulthood, 
60-year-old participants scored higher than 
40-year-old participants on most dimen -
sions. The argument for cohort influences 
on personality trait change is losing traction, 
because these age differences in the Big Five 
traits have been reported for so long.
Studies examining longitudinal changes 
in personality traits have found similar re -
sults. Meta-  analytic estimates of longitudi -
nal mean-level change across the life course 
show significant change in all trait domains 
at some point in the life course (Roberts et 
al., 2006). Extraversion—  specifically, social 
dominance, a subdomain of extraversion 
akin to assertiveness—  increases the most 
during young adulthood. Agreeableness 
shows incremental, if modest, increases with 
age. There is a small increase in conscien -
tiousness during adolescence and marked 
increases throughout young adulthood and 
into midlife. Emotional stability increases 
steadily through midlife. Finally, individuals 
increase in openness to experience during 
adolescence, followed by equivalent declines 
in old age.
More recent cross-  sectional and longitu -
dinal work has provided support for the ar -
gument that people generally become more 
agreeable, conscientious, and emotionally 
stable as they grow older. For example, the 
participants in one longitudinal study tak -
ing place in Iowa increased in constraint, 