fei75766_ch14_435-462.indd 438  02/06/20 01:10 PM
Part V    Biological/Evolutionary Theories438
ways from veryearly inlife.Inonestudy, forexample, Janet DiPietro andher
colleagues (1996) showed thatfetalactivity andfetalheart ratepredict tempera -
ment differences overthefirstyearoflife.Inparticular, ahighheart rateina
36-week-old fetus foreshadowed lesspredictable eating andsleeping habits at3
and6months after birth. Ahighheart ratealsopredicted alessemotional infant 
at6months after birth. Theprenatal environment mayplayanimportant role
inshaping personality. Infact,theamount ofstress themother experiences dur-
ingpregnancy mayaltertheinfant’s ownstress response. That is,infants born to
mothers whohave experienced anunusual amount ofstress during pregnancy tend
tohave impaired stress function; higher baseline levels ofstress hormones; and
afaster, stronger, andmore pronounced physiological response tostress, allof
which persist intochildhood (Barbazanges etal.,1996; Clark &Schneider, 1997).
Secondly, tounderstand howheredity affects behavior andpersonality, psy-
chologists turntothescience ofbehavioral genetics orthescientific study ofthe
roleofheredity inbehavior (Fuller &Thompson, 1960). Theextent towhich 
acharacteristic isinfluenced bygenetics isknown asheritability, aswesawin
theMcCrae andCosta chapter. Researchers usetwin-adoption studies andgene-
by-environment studies tostudy heritability. Twin-adoption studies research into
hereditary influence ontwins, both identical andfraternal, whowere raised apart 
(adopted) andwhowere raised together. Asecond technique inthestudy ofheri-
tability, gene-by-environment interaction research, allows researchers toassess 
howgenetic differences interact withenvironment toproduce certain behavior in
some people butnotinothers (Moffitt, Caspi, &Rutter, 2005; Thapar, Langley, 
&Asherson, 2007). Instead ofusing twins, family members, andadoptees tovary
genetic similarity, gene-by-environment studies directly measure genetic variation 
inparts ofthegenome itself andexamine howsuch variation interacts withdiffer -
entkinds ofenvironments toproduce different behaviors.
Thirdly, biological aspects ofpersonality areassessed using brain imaging tech-
niques, thetwomost common forms ofwhich aretheelectroencephalography (EEG) 
andfunctional magnetic resonance imaging (fMRI). Researchers useelectroencepha -
lography (EEG) torecord theelectrical activity ofthebrain. Theprocedure involves 
placing electrodes onaperson’s scalp. Theelectrodes, metal disks attached towires, 
areusually mounted inafabric capthatfitssnugly overthehead. Typically, theper-
sonisconducting certain tasks while electrical activity isrecorded. EEG issuperior 
toother brain imaging techniques inshowing when brain activity occurs. Itisnotvery
accurate atindicating precisely where activity occurs. Functional MRI (fMRI), does, 
however, tellusabout brain activity. Images from fMRI telluswhere activity inthe
brain isoccurring during particular tasks bytracking blood oxygen useinbrain tissue. 
Inthisway,researchers canseewhich areas ofthebrain areusing themost oxygen 
(andpresumably aremost active) during certain tasks (Lagopoulos, 2007).
Biography of Hans J. Eysenck
Hans Jurgen Eysenck wasborninBerlin onMarch 4,1916, theonlychild ofathe-
atrical family. Hismother wasRuth Werner, astarlet atthetimeofEysenck’s birth. 
Ruth Werner laterbecame aGerman silent filmstarunder thestage name ofHelga Final PDF to printer