fei75766_ch15_463-494.indd 472  02/24/20 10:48 AM
Part V    Biological/Evolutionary Theories472
Humans, however, evolved photoreceptor cells(cones) intheretina thataresensi -
tivetothree different wavelengths oflight, namely red,green, andblue(Jacobs &
Nathans, 2009). Dogs, likemost other mammals, evolved cones sensitive toonly
twowavelengths, namely blueandgreen (Neitz, Geist, &Jacobs, 1989). Humans, 
inother words, havebetter color vision thandogs, butdogshear(and smell) much 
better thanhumans. Another physical mechanism istheimmune system, which 
evolved inresponse totheproblem ofparasites anddisease, justasblood clotting 
developed tosolve theproblem ofdying from wounds orinjury.
Anexample ofareproductive problem issame-sex competition, which stems 
from thefactindividuals must compete withmembers ofthesame sexforaccess to
reproduce withtheopposite sex.Theproblem, therefore, issame-sex competition, or
inBuss’s words: “besting members ofone’s ownsextogainaccess todesirable mem -
bersoftheopposite sex”(1991, p.465). Onesolution, butbynomeans theonly
solution, toreproduction isdominance. Individuals whosuccessfully compete against 
same sexmembers oftheirspecies arethedominant members ofagroup andassuch
theyaregenerally successful atmany specific problems, suchasacquiring resources, 
negotiating social hierarchies, forming successful alliances, andsuccessfully courting a
potential mate (D.Buss, 1988, 1991).
Psychological mechanisms havebehavioral consequences, tactics, andactions 
associated withthem (Buss, 1991, 1999). Forexample, intrasex competition results 
from adominant member inagroup being aleader andisaresult ofsomeone who
could successfully negotiate hisorherplace inahierarchy, fendoffenemies, and
attract mates. Themain jobofanevolutionary model ofpersonality istodescribe, 
study, andexplain these enduring psychological mechanisms.
Evolved Mechanisms
Again, psychological mechanisms areinternal processes thathelpsolve problems of
survival and/or reproduction. Psychological mechanisms relevant topersonality can
begrouped intothree main categories:
• goals/drives/motives
• emotions
• personality traits
Wewillnotsaymuch about goals, drives, andemotions andinstead willfocus 
mostly onpersonality traits asevolved mechanisms. Wewillsee,however, thatgoals, 
motives, andemotions areclosely connected topersonality. Infact,most theories of
personality havecentered around motivation anddrive.
Motivation and Emotion as Evolved Mechanisms
Twogoals andmotives thatactasevolved mechanisms arepower andintimacy. 
These drives takemany different forms, withpower taking theform ofaggression, 
dominance, achievement, status, “negotiation ofhierarchy,” andintimacy taking the
form oflove,attachment, “reciprocal alliance.” Evolutionary psychology refers to
these drives as“adaptations” because theydirectly affect thehealth andwell-being of
theperson.Final PDF to printer