326 III. DEvELOPMENT
dividuals who got married tended to show 
more pronounced decreases in extraversion 
and openness to experience as compared to 
those participants who did not get married 
during the research period. However, this 
study did not distinguish between first and 
later marriages, leaving it open as to what 
degree the transition to the first  marriage 
drove the observed results.
More recently, Denissen and colleagues 
(2019) analyzed six waves of Big Five person -
ality data collected in a nationally represen -
tative longitudinal study of Dutch adults to 
examine selection, anticipation (i.e., chang -
es before the event) and socialization (i.e., 
changes after the event) effects of various life 
events including marriage. This study found 
several selection effects, suggesting that peo -
ple who were high in conscientiousness and 
emotional stability and low in openness were 
more likely to enter marriage. However, this 
study found no evidence for change in any of 
the Big Five traits before or after the transi -
tion to a marital relationship.
In summary, longitudinal research on ro -
mantic relationships and personality trait 
change has frequently, but not always, indi -
cated that the transition to the first commit -
ted romantic relationship is associated with 
decreases in neuroticism. Less frequently, 
studies indicated that entering a serious 
romantic relationship is associated with in -
creases in extraversion. Across all studies, 
the effect sizes of partnership formation on 
personality traits ranged around r = .20. Per -
haps surprising given the societal and indi -
vidual importance attributed to this event, 
evidence concerning the effects of marriage 
on personality change is mixed. Indeed, re -
cent high-  powered studies with multiple as -
sessment waves before and after the transi -
tion to marriage suggest that this life event 
has little impact on personality traits.
Parenthood
The transition to parenthood has been 
viewed as a particularly consequential turn -
ing point in young adulthood that likely 
triggers enduring changes in new parents’ 
personality traits (e.g., Bleidorn, 2015; Blei -
dorn et al., 2018; Hutteman, Bleidorn, et 
al., 2014; Van Scheppingen et al., 2016; van 
Scheppingen, Denissen, & Bleidorn, 2019). 
The birth of a child is typically associated with sudden and oftentimes intense changes 
in new parents’ behavior, thoughts, and feel -
ings, which may translate into both abrupt 
and continuous changes in their personality 
(Bleidorn et al., 2016).
To evaluate whether the birth of the first 
child triggers personality changes in young 
adulthood, Jokela et al. (2009) examined 
whether the transition to parenthood was 
related to changes in sociability (a facet 
of extraversion) and emotionality (a facet 
of neuroticism) across two waves in finish 
sample of 1,839 young adults. They found 
that emotionality remained relatively stable 
in young adults who had no children during 
the 9-year research period but increased in 
participants who had one ( d = 0.14) or more 
children ( d = 0.20). While there was no main 
effect of parenthood on changes in sociabil -
ity, there was a three-way interaction among 
gender, baseline sociability, and number of 
children, suggesting that having children 
predicted increased sociability in men with 
high baseline sociability ( d ~ 0.30) and de -
creased sociability in men with low sociabil -
ity at baseline ( d ~ –0.40). To the degree that 
it replicates in other samples, this finding 
would suggest that having a child can accen -
tuate individual differences in sociability, 
leading extraverted people to become even 
more extraverted, and introverted people to 
become even more introverted.
Using data from a nationally representa -
tive longitudinal study of German adults, 
Specht et al. (2011) found that both men and 
women decreased in conscientiousness after 
the birth of a child compared to individuals 
who did not have children during the study 
period. This finding (recently replicated by 
Denissen et al. [2019]) is puzzling, because 
normative life transitions have been theo -
rized to produce increases (not decreases) in 
conscientiousness. Moreover, the observed 
decrease in conscientiousness runs counter 
to the well-  documented normative increase 
in conscientiousness in young adulthood. 
One possible explanation for this finding 
may be that even those parents who raise 
their conscientiousness to meet the demands 
of parenthood may not actually perceive 
themselves as being more conscientious, be -
cause their lives does not feel any more orga -
nized, orderly, disciplined.
Consistent with this hypothesis, Van 
Scheppingen et al. (2019) found decreases in 