fei75766_ch15_463-494.indd 476  02/24/20 10:48 AM
Part V    Biological/Evolutionary Theories476
bywhich hemeant thatchildhood experiences make some behavioral strategies 
more likely thanothers. Anexample ofsuchcalibration isifpeople grow upwithout 
afather present, theyaremore likely tobesexually active atayoung ageandhave
more sexpartners during adolescence andadulthood. People inthissituation culti-
vateamore promiscuous sexual strategy because parental attention isnotreliable 
andadult relationships areviewed astransient (Belsky, Steinberg, &Draper, 1991).
Another example ofearlycalibration ofadaptive strategies isattachment style, as
wefirstdiscussed intheKlein chapter (5).Attachment between care-giver andinfant is
inherently adaptive—without suchanattachment thebabydoesnotsurvive thefirstfew
weeks oflife(Buss &Greiling, 1999). Adult attachment increases support, protection, 
andreassurance, andifattachment isthemodel thechild experiences, thenheorshe
islikely todevelop similar relationships inadulthood. Similarly, avoidant attachment 
signals parental unwillingness toinvest inthechild.
Asecond origin ofenvironment induced individual differences isalternative 
niche specialization, which means thatdifferent people findwhat makes them stand 
outfrom others inorder togainattention from parents orpotential mates. Oneexam -
pleofniche specialization isseeninbirth order, aswesawintheAdler chapter (3).
Children ofdifferent birth orders gravitate toward different personalities, interests, 
andactivities because thatistheonlywaytogainattention from theirparents. Frank 
Sulloway (1996) argued thatfirstbornfindtheir“niche” byidentifying withparents 
andauthority figures, whereas second andlatter borns findtheir“niche” bybeing 
focused onoverthrowing those inpower (i.e.,older siblings).
Heritable/Genetic Sources
AswesawintheEysenck andMcCrae andCosta chapters, heritability istheextent 
towhich atraitisunder genetic influence. Body type, facial morphology, anddegree 
ofphysical attractiveness actasheritable sources ofindividual differences (Buss &
Greiling, 1999). Thatis,muscular menormenwithmasculine, dominant looks will
garner more female attention, which willleadtomore opportunities forsexual activ-
ity,thanwillthinmenormenwithlessdominant looks (Mazur, Halpern, &Udry, 
1994). These areheritable because theshape ofone’s faceorbody ismostly con-
trolled bygenetics.
Nonadaptive Sources
Some sources ofindividuals donotbenefit survival orreproductive success andhence 
arecategorized as“nonadaptive.” Themost common nonadaptive source ofindivid -
ualdifferences isneutral genetic variations, which most often taketheform ofgenetic 
mutations. Some mutations areneutral inthattheyareneither harmful norbeneficial 
totheindividual. They maystayinthegenepoolindefinitely untilpressures ofnatural 
orsexual selection eliminate them.
Maladaptive Sources
Maladaptive traits arethose thatactively harm one’s chance forsurvival ordecrease 
one’s sexual attractiveness. These canstem from either genetic orenvironmental 
sources. Onegenetic source isgenetic defect, butinthiscase, themutation isFinal PDF to printer