fei75766_ch13_408-434.indd 423  02/06/20 01:05 PM
Chapter 13    McCrae and Costa’s Five-Factor Trait Theory423
Postulates for Basic Tendencies
Basic tendencies havefourpostulates: individuality, origin, development, andstructure. 
Theindividuality postulate stipulates thatadults haveaunique setoftraits andthateach
person exhibits aunique combination oftraitpatterns. Theprecise amount ofneuroti -
cism, extraversion, openness, agreeableness, andconscientiousness isunique toallof
us,andmuch ofouruniqueness results from variability inourgenotype. Thispostulate 
isconsistent withAllport’s ideathatuniqueness istheessence ofpersonality. 
Second, theorigin postulate takes aclear ifsomewhat controversial stance: All
personality traits aretheresult solely ofendogenous (internal) forces, suchasgenet -
ics,hormones, andbrain structures. Inother words, thefamily environment plays 
noroleincreating basic tendencies (butagain, recall thatpersonality traits arenot
synonymous withpersonality asawhole). Figure 13.3shows butonecausal arrow 
going from biological bases tobasic tendencies. Such aclaim isbased mostly onthe
robust findings from behavioral genetics thatthefivedimensions ofpersonality can
bealmost exclusively explained (about 50%each) bytwofactors, namely genetics 
andnonshared environment (Hamer &Copeland, 1998; Loehlin, 1992; Plomin &
Caspi, 1999). Genetic influence isdemonstrated bywhat behavioral geneticists refer
toasheritability coefficients andcomes outoftheresearch onadoption studies and
twinstudies. Heritability addresses thequestion ofwhat isthedifference inthecor-
relation onagiven personality traitbetween individuals whoaregenetically identical 
(identical twins) andthose whoshare onlyabout 50%oftheirgenes (allother sib-
lings). Ifgenes played noroleinshaping traits, nodifferences would befound incor-
relations between people whovaryintheirdegree ofgenetic similarity. Identical and
fraternal twins would bejustassimilar orjustasdifferent. Evidence indicates that
identical twins, evenifreared indifferent environments, show greater similarity in
personality thanother siblings. Andinthecaseofmost personality traits, thedegree 
ofsimilarity suggests thatabout 50%ofthevariability inpersonality isduetoherita -
bility orgenetics. Most oftheremaining 50%isexplained bynonshared experiences 
ofsiblings ofvarying ages; thatis,siblings usually havedifferent experiences, friends, 
andteachers. Forinstance, parents change theirownparenting behaviors withtime
andexperience. Thus, achild born three orfouryears afteranother isbeing raised 
inasomewhat different environment. More recent research hasuncovered genetic 
regions associated withallfivedimensions ofpersonality (deMoor etal.,2012).
Third, thedevelopment postulate assumes thattraits develop andchange 
through childhood, butinadolescence ,theirdevelopment slows, andbyearly tomid-
adulthood (roughly age30),change inpersonality nearly stops altogether (Costa &
McCrae, 1994; Costa, McCrae, &Arenberg, 1980).
McCrae andCosta (2003) speculated thatthere maybesome evolutionary 
andadaptive reasons forthese changes: When people areyoung andestablishing 
their relationships andcareers, highE,O,andevenNwould bebeneficial. Aspeo-
plemature andbecome settled, these traits arenolonger asadaptive astheywere 
earlier. Moreover, increases inagreeableness andconscientiousness might behelp-
fulaspeople age.Inoursection onresearch, wediscuss stability oftraits during 
adulthood.
Finally, thestructure postulate states thattraits areorganized hierarchically 
from narrow andspecific tobroad andgeneral, justasEysenck (1990) hadsug-
gested. Thispostulate grows outofMcCrae andCosta’s long-held position thattheFinal PDF to printer