fei75766_ch15_463-494.indd 480  02/24/20 10:48 AM
Part V    Biological/Evolutionary Theories480
thepoint where two-thirds ofadult Americans arenoweither overweight orobese 
(Flegal etal.,2010). Iftheywereoptimally designed theywould bemore efficient and
respond more quickly tochanges intheenvironment.
Related Research
Theevolutionary model ofpersonality cannot betested directly insofar aswecannot 
conduct studies overhundreds ofgenerations. Andyet,justlikeinbiology, there is
much support fortheevolutionary basis ofhuman personality, which canbedivided 
intoatleastthree general topics: traits asfitness, genetics, andanimal personality. All
three linesofevidence support theviewthatpersonality hasabiological basis and
thatthese biological systems haveevolved.
Evolutionary Origins of Personality: Traits as Related to Fitness
Acentral ideaofevolutionary theory isthatoffitness, thatis,anorganism’s ability to
survive andreproduce. Personality traits exist, according toBussandother evolution -
arypsychologists, because theyincrease anindividual’s fitness andmake himorher
more likely tosurvive andreproduce. Recall thatBussargued thatpersonality traits 
aresolutions toevolved problems ofsurvival andreproduction. Forexample, domi -
nance isasolution forhowtoattract amate; conscientious isasolution forwhom 
totrust; andsocial-emotional intelligence isasolution forfiguring outwhom tomate 
with. Similarly, Nettle (2006) argued forevolutionary costs andbenefits ofpersonal -
itytraits (seeTable 15.2). Forexample, extraversion-dominance hasthebenefit of
attracting mates, butatthepotential costs offamily stability; conscientiousness, how-
ever, mayhavethebenefit ofleading togreater fitness andbetter health, butatthe
potential costs ofobsessiveness orrigidity.
Butaswediscussed inthebeginning ofthechapter, some evolutionary psychol -
ogists haveargued against personality traits asadaptations. Iftraits wereadaptive 
(increase fitness byincreasing survival rates andreproductive success), thennatural 
selection should winnow outofthepopulation traits thatarenotadaptive. Yetvaria -
tionintraits exists. Some people areveryanxious andsome arecalm; some arevery
dominant andoutgoing andothers meek andshy.
There aretworelated evolutionary explanations forpersonality traits, bothof
which relate tofitness. First, asBussargued, personality traits existbecause they
solve survival andreproductions problems—that is,theyincrease thefitness ofthe
individual. Second, theymayexistbecause theywereselected, notsomuch bynature 
(natural selection), butbyother people intheprocess ofchoosing amate (sexual 
selection). Remember thatsexual selection istheprocess bywhich traits thatare
deemed attractive bytheopposite sex(strength, intelligence, attractiveness, status, 
power, etc.). AsDarwin firstpointed out,sexual selection isaresult ofdifferences in
reproductive success. Sexual selection, therefore, isconnected tofitness (reproductive 
success). 
Asisoften asked about ideas inevolutionary psychology, howcanwetestthe
hypothesis thatpersonality traits arerelated toevolutionary fitness, since obviously 
wecannot gobackintimeandstudy ourancestors inearly evolutionary time
periods? Onemethod employed bypsychologists andanthropologists istostudy Final PDF to printer