fei75766_ch15_463-494.indd 464  02/24/20 10:48 AM
Part V    Biological/Evolutionary Theories464
Davidwasa17-year-old highschool drop-out, arrested twice ondrugcharges, and
wasworking thenight shiftatatruck stop. Onenight, adrunken driver threat -
ened totakeanaxandchop offhislonghair.Another night, ayoung manbeatDavid 
withaclubfornoapparent reason other thantostartafight. Atthispoint, David 
decided there must beabetter waytomake aliving andsoheenrolled innight school 
tofinish hishighschool diploma. After doing so,hegotverylucky: Hewonaran-
domlottery toenter theUniversity ofTexas atAustin, forwhich hedidnothavethe
required GPA. Incollege, hisintellectual curiosity blossomed. Asheputit,“Inmy
junior year, Iknew thatIwanted tobecome ascientist andthatthehuman mind was
theterritory Iwanted toexplore” (D.Buss, 2004, p.16).Tenyears later, David wasa
professor ofpsychology atHarvard University!
How doesahighschool drop-out become aprofessor atHarvard? Oneofthe
ideas thatsparked thisinterest inlearning andunderstanding inDavid wasthecon-
ceptofevolution, especially when applied tohuman personality, thought, andbehav -
ior.More specifically, itwashisinterest insexandallthebehaviors thatgowith
it—attraction, lust,jealousy, cheating, flirting, gossip—that focused hiscareer ambi -
tions. Thisspark catapulted Bussfrom highschool drop-out toHarvard professor. To
befair,David wasnever atypical drop-out: Hisfather wasadistinguished professor of
psychology andhiswhole family wasintellectually curious andtalented.
Overview of Evolutionary Theory
Charles Darwin (1859) laidthefoundation forthemodern theory ofevolution, even
though thetheory itself hasbeen around since theancient Greeks. Darwin’s major 
contribution wasnotthetheory ofevolution butrather anexplanation forhowevo-
lution works, namely through selection (natural andsexual) andchance. Chance 
occurs mostly through random genetic mutation, andwewon’t havemuch tosay
about chance. Instead, wefocus onselection ofthree different kinds.
Inorder tounderstand natural andsexual selection, let’sfirstexamine asimilar 
concept created byhumans andonethatprovided Darwin withhiskeyinsight: artificial 
selection. Artificial selection (otherwise known as
“breeding”) occurs when humans select particular 
desirable traits inabreeding species. Forexample, 
thedifferences between theverylarge Great Dane 
andtheverysmall Chihuahua havecome about by
humans  selecting these qualities inthese breeds. 
Humans havebeenbreeding plant andanimal spe-
ciesforthousands ofyears.
Natural selection issimply amore general 
form ofartificial selection inwhich nature rather 
thanpeople select thetraits. More specifically, it
occurs when traits become either more orlesscom-
moninaspecies overlongperiods oftimebecause 
theydoordonotleadtogreater survivability (D.
Buss, 1999; D.Buss&Greiling, 1999). Inthis
way,natural selection involves “evolved strategies” 
foraspecies’ survival. Butunderstand thatthese 
“Traits, suchassize,aresometimes artificially selected forby
humans, andcanleadtodifferent breeds ofdog.”
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