272 III. DEvELOPMENT
lationship to another, and despite having 
different partners with different personali -
ties, they could maintain the same type of 
romantic partner role across partners (e.g., 
the avoidant type). To our knowledge, this 
idea has yet to be tested empirically, but 
there is indirect evidence in studies showing 
that people maintain similar levels of rela -
tionship dissatisfaction resulting from neu -
roticism across different partners (Robins et 
al., 2002). Some existing findings even con -
tradict the role continuity principle. Staying 
in a relationship longer (i.e., maintaining a 
consistent role) is related to greater chang -
es in personality traits (Neyer & Lehnart, 
2007; Robins et al., 2002). Yet this principle 
suggests that experiencing a consistent role 
within a relationship would lead to more, 
rather than less, consistency in personality 
traits.
The Identity Development  Principle
The identity development principle describes 
the process of developing, committing to, 
and maintaining an identity over time. This 
process may lead to greater personality 
consistency (Roberts & Caspi, 2003). Ac -
cording to this principle, identity develop -
ment leads to more personality consistency 
because it results in a clearer perspective to 
aid in making important decisions. A clear, 
strong identity can serve as a filter for life 
experiences; this should lead individuals to 
interpret new experiences in a manner that 
is consistent with their identities. Only one 
study has examined identity structure and 
personality continuity, and the results in -
dicate that self-  concept clarity is unrelated 
to personality consistency (Lodi-Smith et 
al., 2017). Because one study is insufficient 
to draw any notable conclusions, more re -
search is necessary to evaluate the identity 
development principle.
The neo-  socioanalytic principles of per -
sonality development, derived from the 
observations of personality development 
across a critical mass of longitudinal stud -
ies, provide a set of concrete, testable prin -
ciples and corollary hypotheses that can be 
supported or refuted with ample data. While 
many of the principles describe developmen -
tal patterns, they only indirectly point to 
the mechanisms that explain those patterns. In the next section, we look further at the 
mechanisms that may explain the patterns 
described by the principles of personality de -
velopment.
Person–Environment Transactions 
and Personality  Development
The links between personality development 
and the ways people interact with their en -
vironment were discussed long before per -
sonality development was a focal chapter 
in this handbook (Buss, 1987). Beginning 
with transactional processes (i.e., selection, 
evocation, and manipulation), personality 
psychologists have discussed ways in which 
people interact with their environment and 
how those interactions result in continuity 
and change in personality. Moreover, recent 
work has gone on to differentiate and identi -
fy the components and mechanisms at a very 
molecular level that underlie these broader 
person–  environment transactions (Baumert 
et al., 2017; Wrzus & Roberts, 2017). Rath -
er than going through these many processes 
and mechanisms one by one, we describe 
two hypothetical case studies, moving from 
adolescence into young adulthood and be -
yond, and use these to illustrate how these 
mechanisms might come into play to both 
create continuity and promote change.
Consider two hypothetical 21st-  century 
American teenagers named Carol and Tom. 
Carol is studious, serious about school, and 
plans to attend college after high school. 
Tom is a talented athlete, an average student, 
and has not thought seriously about college 
but also has not ruled it out. In their junior 
year of high school, Carol practices for and 
achieves a high score on the American Col -
lege Test (ACT) and standardized achieve -
ment test (SAT). Tom takes the SAT because 
he is forced by the school and does not take 
it seriously. In the spring of his junior year, 
however, Tom is contacted by a college re -
cruiter for basketball and asked whether he 
would like to attend a specific college on an 
athletic scholarship.
Even with this minimal information 
one can see two transactional processes in 
play—  selection and attraction. Attraction  
refers to people being drawn to personality- 
consistent environments in which they be -