Several other biological mechanisms clearly affect personality . In
the 19th century Phineas Gage survived an accident that left a metalshaft lodged in his brain. He was observed afterward to have had pro -
found changes in personality traits, becoming irritable and impulsive.
Neurologists have documented thousand of cases of traumatic brain in -
jury since then, with attendant changes in personality (Costa & Mc -
Crae, 2000a). Similarly , disease processes can affect the brain and,
through it, personality traits. Siegler and colleagues (1991) were thefirst to show the effects that dementing disorders like Alzheimer’s dis -
ease have on personality traits—most notably , a precipitous decline in
Conscientiousness. Mental disorders like schizophrenia and acute de -
pression also affect personality traits, and pharmacological treatments
can reverse many of these effects (P . D. Kramer, 1997).
The astute reader will note that some of these examples illustrate a
sense in which the environment can be said to affect Basic Tendencies:by altering the underlying biology . Figure 10 might well be modified byadding another arrow between External Influences and Biological Bases.That would add another important pathway without affecting the basicdistinctions drawn by FFT.
Conflicting Evidence
Although the Origin postulate of FFT appears to have considerable sup-port, it must be pointed out that there are several bits of evidence thatcontradict it by suggesting a direct effect of the environment on person-ality traits. Clinical depression can be successfully treated by conven -
tional psychotherapy as well as by drugs (VandenBos, 1986); presum -
ably that therapy also affects personality traits. Life events per se usually
do not change personality trait levels, but some specific events appar -
ently do. For example, Costa, Herbst and colleagues (2000) found that
women who were divorced in the 6-year period before a longitudinalreadministration of the NEO-PI-R became somewhat more open andextraverted compared to women who got married in the same period, asif divorce were a liberating event —and marriage a constraining event.It was not clear, however, how long lasting the changes would be, be -
cause there was no follow-up. Again, an acculturation study of Hong
Kong Chinese undergraduates who had moved to British Columbia sug -
gested that residence in Canada led to higher levels of Openness and
Agreeableness (McCrae, Yik, Trapnell, Bond, & Paulhus, 1998).196 PERSONALITY IN ADULTHOOD