fei75766_ch15_463-494.indd 469  02/24/20 10:48 AM
Chapter 15    Buss: Evolutionary Theory of Personality469
think. Evolution alsostarts withtheassumption thatindividual members ofanyspe-
ciesdiffer from oneanother. Inthissense, thetwowould appear tobeperfect part-
ners. Given thefactthatbothpersonality andevolution haveindividual differences as
theirstarting point, youwould havethought thatthemarriage ofthetwowould have
been obvious andhappened soon afterDarwin suggested itwould inthemidtolate
19thcentury.
Yetfewtookupthechallenge andthemarriage didnothappen untilthe
1990s. Infact,astwoofthemain proponents ofevolutionary psychology—Tooby 
andCosmides—pointed outearly inthemarriage, there wasaserious problem: nat-
uralselection typically works tolessen individual differences insofar thatsuccess -
fultraits andqualities become thenorm andlessadaptive traits dieout.Over long
periods oftime, nature isselecting thesame trait.Toputitmost clearly, there is
aparadox here: “Ifnatural selection winnows outmaladaptive traits andoverthe
long-term produces auniversal human nature thenhowcanindividuals consis -
tently differ intheirdisposition tothink andbehave (i.e.,havepersonality)?” 
(Tooby &Cosmides, 1990). Human adaptations should remain universal and
species-typical, meaning there should notbesignificant differences between individu -
als.Indeed, Tooby andCosmides argue thatbydefinition ifatraitshows significant 
individual differences itcannot beanadaptation, because bydefinition adaptations 
arespecies typical. Tobeclear, Tooby andCosmides werenotsomuch denying 
theexistence ofpersonality astheyweredenying thatitwasanadaptation. Andyet
fewdeny thatpersonality andindividual differences exist. How doweexplain this
paradox?
Indeed, early initsdevelopment thefieldofevolutionary personality psychol -
ogyitself wasdivided overhowtosolve thisparadox. Some leading evolutionary 
psychologists argued fortwosolutions: personality differences were either “noise” or
theywere perhaps “by-products” ofevolved adaptive strategies (Tooby &Cosmides, 
1990). More recently, however, other theorists havemade thecaseforpersonality 
traits being something more thannoise orby-products, namely adaptations (D.Buss, 
1991, 1999; MacDonald, 1995; Nettle, 2006; Nichols, Sheldon, &Sheldon, 2008). 
Because David Busswasthefirstandmost prominent theorist totakeupthecause 
ofdeveloping anevolutionary theory ofpersonality, wefocus onhistheory. Later in
thechapter, webriefly review afewoftheextensions byneo-Bussian theorists. The
essence ofBuss’s theory ofpersonality revolves around adaptive problems andtheir
solutions ormechanisms. Before discussing adaptations andtheirsolutions, letus
firstreview thenature andnurture ofpersonality.
The Nature and Nurture of Personality
Recall thatpersonality isallabout consistent andunique differences between indi-
viduals inhowtheythink andbehave. Thequestion quickly becomes, “What causes 
these individual differences?” Aswithallquestions about human behavior itcomes 
down totwofundamental answers: nature and/or nurture. Thatis,behavior andper-
sonality arecaused byeither internal qualities orexternal-environmental ones. Itis
easytosee,however, thatthisdichotomy isafalseone.Internal states andprocesses, 
from biological andphysiological systems topersonality traits, come about from input Final PDF to printer