fei75766_ch15_463-494.indd 477  02/24/20 10:48 AM
Chapter 15    Buss: Evolutionary Theory of Personality477
harmful totheperson. Anenvironmental source isseeninenvironmental trauma, 
suchasbrain orspinal cordinjury, which canalsoleadtomaladaptive individual 
differences.
Neo-Bussian Evolutionary Theories of Personality
David Busswasthefirsttoformally propose acomplete evolutionary theory ofper-
sonality, butothers havefollowed andmade advances tothetheory. MacDonald 
(1995), forexample, furthered Buss’s theory withtwomain contributions. First, he
tiedpersonality more closely toevolved motivational andemotional systems, andsec-
ond,heargued thattherange ofpersonality variation weseeonthemain dimensions 
ofpersonality isviable alternative strategies formaximizing fitness.
MacDonald, similar toBuss, alsotiedpersonality dimensions toevolved 
strategies forsolving adaptive problems. These behavioral strategies are
connected either withmotivation toapproach oravoid situations orwiththe
emotional system ofnegative orpositive affect. MacDonald, however, onlyhad
fourpersonality dimensions (dominance, conscientiousness, nurturance, and
neuroticism) andleftoutopenness.
MacDonald further argued thatitisadaptive foraspecies toproduce individu -
alsthatvaryalong acontinuum intheir responses toimportant problems because 
changing environments require different responses. Thatiswhat MacDonald means 
by“viable alternative strategies formaximizing fitness.” Forinstance, inrelatively 
safeenvironments, anxiety andvigilance arenotasadaptive astheyareinrelatively 
dangerous environments. Animals canafford tobeboldinsafer environments. 
Some environments mayfavor risktakers andother environments mayfavor risk
avoiders. Indeed, innonhuman animals weseejustsuchadaptive changes tochang -
ingenvironments (Nettle, 2006). Forexample, inGuppie fishpopulations withrela-
tively fewpredators, boldness isacommon trait, butifpredators areintroduced, this
traitbecomes lesscommon injustafewgenerations (cf.O’Steen etal.,2002). Note 
too,these traits areheritable andhaveagenetic basis, which isonecriterion foran
adaptation.
Similarly, Nettle (2006) recently expanded onevolutionary theories of
personality andargued thatTooby andCosmides’s (1990) argument thatpersonality 
could notbeanadaptation failed toappreciate howenvironmental change andvari-
ability would ultimately select forindividual differences inbehavior within agiven 
species. Nettle (2006) reviewed numerous studies from thenonhuman animal lit-
erature thatreport howsudden changes intheenvironment (justafewgenerations), 
increased theproportion ofanimals thathadtraits adaptive tothatenvironment. 
When theenvironment switched backtotheoriginal conditions, animals onthe
other endofthatdimension became more common again. Forexample, some female 
chickadees areboldandexploratory, whereas others areinhibited. Infood-poor years, 
themore exploratory birds aremost likely tosurvive (Dingemanse, Both, Drent, &
Tinbergen, 2004). Infood-rich years, however, thebolder andmore exploratory 
female birds arelesslikely tosurvive, possibly because theyaremore likely tobecome 
involved indangerous encounters withpredators. Inshort, evolution favors individual 
differences because onecannever predict what thefuture holds andwhich qualities 
willbestmatch changes intheenvironment.Final PDF to printer