considered169pp

PARTIBiologicalandGeneticProcessesCHAPTERONEBehaviorGeneticsandAdolescentDevelopment:AReviewofRecentLiteratureJosephLeeRodgersandDavidE.
BardIntroductionBehaviorgeneticsisaquantitativemethod,andadolescentdevelopmentisapsychologi-caltopic.
Treatingthecrossbetweenthesetwoarenasappears,atthesurface,torequirecollectingresearchinwhichthemethodhasbeenappliedtostudythetopic,andreview-ingthatresearchforcoherenceandcommonthemes.
Butthechallengeisrathermoredifcultthanthesurfacelevelviewmightsuggest.
Belowthesurfaceisagreatdealofshiftingsand,whichmakesorganizingthetopicdifcult.
Becauseofthisinstability,itiscriticalthatwecarefullyandexplicitlydeneafoundationalstartingpoint.
Intheintroductiontothisarticle,webeginwithsomedenitions,andthenwedescribethedifcultiesinherentinreviewing"behaviorgeneticsandadolescentdevelopment.
"Weconcludeourintroductionwithasummaryofthefoundationonwhichwewillbaseourreview.
Inthenextsection,wecarefullybuildthatfoundation.
Following,wesummarizetherelevantresearch,andembeditwithintheorganizationalfoundation.
Denitions:WhyIsThisChapterDifculttoFrameThestartingpointformostbehaviorgeneticmodelingistheconceptualpartitioningofsourcesofvarianceintogenetic,sharedenvironmental,andnonsharedenvironmental(e.
g.
,Rowe&Plomin,1981).
Someofthesimilaritybetweenindividualsinthesamefamilymaybecausedbysharingthesamegenes.
Forexample,monozygotic(MZ)twinsshare100percentoftheirgenes,andshouldbeapproximatelyidenticalontraitsorbehav-iorsthatarestronglyundergeneticcontrol(e.
g.
,height,eyecolor).
Dizygotic(DZ)twinsandfullsiblingsonaverageshare.
50oftheirgenes,halfsiblingsshare.
25,cousinsshare.
125,etc.
Alternatively,someofthesimilaritybetweenindividualsinthesamefamilyhasasitsetiologicalsourcethesharedenvironment;thistheoreticalsourceofinuencecausesrelatedindividualstobesimilarbecausetheyshareacommonenvironmentwithinthefamily.
Forexample,parentaldisciplinestylemaybeasharedenvironmentalinuencethatisincommontoallchildreninafamilyandthatresultsinsimilaritiesbetweenthechildreninameasureofresponsetoauthority.
Finally,thenonsharedenvironmentisatheoreticalsourceofinuencethatcausesindividualsinthesamefamilytobedifferentfromoneanother,thatis,theseinuencesarenotsharedincommonamongsiblings.
Forexample,aparticularlyoutstandingteacherthatachildhadinrstgrade(butwhowasnottheteacheroftheotherchildreninthefamily)couldcreatenonsharedenvironmen-talinuencesonreadingmotivation.
Or,evenwithinthefamily,parentsmaybemoreauthoritativewiththeirsonsthanwiththeirdaughters(whichwouldresultinparentaldisciplinestylebeinganonsharedratherthansharedenvironmentalinuence).
Itiswellknowntobehaviorgeneticists–ifnotnecessarilytothegeneralpopulationofresearchers–thatmeasuresofvariancerelatedtogeneticprocesses(heritabilities,orh2)andsharedenvironmentalprocesses(sometimescalledthecommonenvironment,orc2)arenotimmutable(seeAngoff,1988).
Thebasicbiometricalmodel(e.
g.
,Falconer,1981)partitionstheoverallvarianceinthedependentvariableintothatattributabletogenes,thatattributabletothesharedenvironment,andthatattributabletothenonsharedenvironment.
(Mostestimationproceduresconfoundthelattersource–nonsharedenvironmentalvariance,oftencallede2–withmeasurementerror,althoughtherearestatisticalwaysaroundthisproblem;seeRodgers,Rowe,&Li,1994.
)Twocriticalfeaturesofthisdenitionmustbeappreciated.
First,h2,c2,ande2dependonboththeamountofvariancerelevanttotheirconceptualdomain,andtheyalsodependontheamountofoverallvariance.
Theconceptualformulasareh2=geneticvariance/totalvariance,c2=sharedenvironmentalvariance/totalvariance,ande2=nonsharedvari-ance/totalvariance.
(Totalvarianceisoftenreferredtoas"phenotypicvariance"inthebehaviorgeneticliterature.
)Thesethreecoefcientsnecessarilyaddupto100percent,sothateachonemaybeinterpretedastheproportionoftotalvarianceattributabletogenetic,sharedenvironment,andnonsharedenvironmentsources,respectively.
Thus,forexample,ifgeneticvarianceremainsxed,butoverallvarianceinthedependentvariable(phenotypicvariance)increasessubstantially,thenh2goesdownduetothedenominator,withoutanyshiftinthegeneticcontributionitself.
Second,h2,c2,ande2mustbeinter-pretedinavariancecontext;thatis,thegeneticandenvironmentalcontributionsexplainindividualdifferences,andnotgeneralpropertiesoftraitsorbehaviors.
Forexample,genesperfectlydetermineeyecolor.
Yet,inasettingwithfewnon-brown-eyedpeople,heri-tabilitywouldbeverylow(becausethereislittlephenotypicvariation).
Inotherwords,h2indicateshowmuchvarianceinatraitorbehaviorisrelatedtogeneticsources.
Itdoesnotindicatewhethertheexistenceofthetraitorbehaviorhasanygeneticetiology.
Sim-ilarly,c2ande2indicatehowmuchvarianceinatraitorbehaviorisattributabletothesetwoenvironmentalsources,notwhetherthetraitorbehaviorhasunderlyingenviron-mentetiology.
Forexample,aperson'saccentisobviouslyinuencedbytheenvironment.
Butameasureofaccentwouldshowverylowc2,forthesimplereasonthatthereisverylittleoverallvariancetoexplain.
Evenotherwiseresponsiblebehaviorgeneticistsoftenmisusetheirlanguage,andreferto"geneticorenvironmentalinuencesonatrait,"when4JosephLeeRodgersandDavidE.
Bardwhattheyreallymeanis"geneticorenvironmentalinuencesonvarianceinorindi-vidualdifferencesinatrait.
"Theexplanationabovereferstothebasicadditivegeneticmodel.
Thismodelimpliesthatanumberofseparategeneticsourceseachcontributeseparateandadditivepiecesofinuencesonthevarianceinatraitorbehaviorofinterest.
Ofcourse,somegeneticprocessesarenonlinearandnonadditive(e.
g.
,basicprinciplesofMendelianinheritanceareinherentlynon-additive).
Quantitativemodelinginbehaviorgeneticssupportsttingdominancemodels(e.
g.
,Neale&Cardon,1992),andtheconceptofemergenesishasbeenproposedtoaccountforconguralgeneticcontributions(Lykkenetal.
,1992).
Ontheotherhand,anothertypeofnonlineargeneticprocess,epistasis,involvesgeneticinter-actionsofallelesacrossgeneticloci(asopposedtoMendeliandominance,whichinvolvesinteractionsofalleleswithinageneticlocus).
Epistasisisdifculttomodelinbehavioralgeneticsettings(e.
g.
,Neale&Cardon,1992).
Inthisreview,wewillfocusoneffortstotadditivegeneticmodelstoadolescentdata,primarilybecauselittleattentionhasbeengiventononlinearornon-additivemodelsintheliterature.
Besidesgeneticnonadditiv-ity,asecondproblemoccurswhentherearegenetic-environmentalinteractionsthatarenotaccountedforwithinthemodel.
Turkheimer(1998)showedthattheeffectoffailingtoaccountforgenetic/environmentalinteractionsistobiasestimatesofh2andc2.
Whilethereislittlepublishedliterature,effortstoaccountforgene-environmentinteractionsareongoing(andseveralwillbementionedinreviewingtheliterature).
Bothh2andc2(and,implicitly,e2)canshiftandchangeovertimeandoverage,asthevariancesinboththenumeratorsandthedenominatorsshiftandchange.
Atadolescenceinparticular,phenotypicvarianceinmanytraitsandbehaviorscanshiftsubstantially.
Forafewyears,height(andmostotherphysiologicalmeasures)becomesmorehighlyvari-able,aschildrenreachpubertyatawiderangeofages.
Inlessobviousways,therecanbeshiftsinoverallvarianceofintelligence,manypersonalitytraits,andespeciallyinsocialandhealthbehaviors.
Smokingprovidesagoodexample.
Among8-year-olds,smokingbehaviorhasvirtuallynoheritability.
Obviously,thisisnotbecausegeneticinuencesdonotcontributetosmokingingeneral,butbecausethereislittlephenotypicvarianceinmeasuresofsmokingamong8-year-olds.
Byage14,smokingheritabilitiesbegintobedetectableinameasurelikeage-at-rstcigarette(butnotsomuchinmeasuresofsmokingaddiction).
Byage20,measuresofsmokingintensity,smokingduration,andsmokingaddictionallshowheritablecomponents.
Thesepointsaboutgeneticinuencesapplyequallytobothsharedandnonsharedenvironmentalinuencesaswell.
Itisinthiscontextthatwerefertothe"shiftingsand"onwhichweobservegeneticandenvironmentalinuences.
Thereareseveralproperwaystotreattheseproblems.
Therstisinterpretational;authorsmustbeclearaboutwhath2,c2,ande2mean,andwhattheydon'tmean.
Second,therearedirectmeasuresoftheseinuences;forexample,somebehaviorgeneticistsemphasizetheimportanceofcomputingheritabilities,andalsocomputingcoefcientsofgeneticvariation,whicharenotaffectedbytheoverallvarianceoftheDVitself(see,e.
g.
,Houle,1992).
Third,theshiftsinh2andc2valuescanprovideagreatdealofinforma-tioninandofthemselves.
Forexample,Kohler,Rodgers,andChristensen(1999)docu-mentedasubstantialshiftinh2offertility,usingseculartwindatafromDenmark.
Thedramaticupwardshiftsinh2valuesthattheyobservedoccurredsimultaneouslywiththeBehaviorGeneticsandAdolescentDevelopment5twofertilitytransitionsinDenmark,whichprovidedaframeworkwithinwhichtoexplainthisrapidchangeinheritability.
Thedifcultiesdenedinthisintroductorysectionareallrelatedtothemethod(and,importantly,toimproperinterpretationofthedesignandpurposeofthemethod).
The"shiftingsand"problemofinterpretingheritabilitiesisonlyaproblemifitisallowedtobe.
Wewillattempttocarefullyextracttheproperinformationfromthestudieswereview,andweinvitethereadertobringhealthycriticalinspectionintothisinvestigationwithus.
AsMaccoby(2000)noted,"knowingonlythestrengthofgeneticfactors.
.
.
isnotasufcientbasisforestimatingenvironmentalones"(p.
1).
Turkheimer(1998)suggestedthatheritabilitystudiesleadonlytothe"banaltautologythatallbehaviorisultimatelybasedinthegenotypeandbrain"(p.
782).
WhilewearemoresanguineaboutthevalueofsuchstudiesthanTurkheimer,weapplaudtheskepticalapproachthatthispositionimplies.
Finally,weintendtorespondtothe"shiftingsand"problembyrmlytyingdownourtreatmentwiththeoreticalorientationsfrombothsocialandbiologicaldomainsthatfocusonthetopicandnotonthemethod.
Thestudyofadolescenceingeneral,andespeciallyadolescentdevelopment,focusesattentionontheprocessofchange.
Wehaveusedthreedifferentsocialtheoriesinourpastworktoframetheprocessofadolescentdevelopment.
Moreproperly,theseareclosertomotivatingorientationsthantheyaretoformaltheo-ries,becauseweinnosensetestorevaluatethestructures.
Rather,weletthemguideourinvestigationandreview.
ThethreeapproachesaretheTransitionBehaviorPerspective,theLifeCoursePerspective,andProblemBehaviorTheory.
Inaddition,thebiologicalperspectivethatbestinformsthestudyofadolescentdevelopmentistoconsiderhormonalinuencesthataffectbothphysiologicalchangesandbehavioralchanges.
TheoreticalFrameworkAdolescenceembeddedinasocialandtemporalecologyTheTransitionBehaviorPerspectiveisdevelopedmorecompletelyinEnsminger(1987)andinRodgersandRowe(1993).
Thisorientingframeworkviewsadolescenceasaperiodofexpandedbehavioralopportunity.
Adolescentsbegintohavechoiceswithinabehav-ioralecologythatwerenotavailabletothemduringchildhood.
Howmuchtostudy,whethertosmokeanddrink,whatpartiestoattend,whatschoolclubstojoin,andman-agementofhealthbehaviorsareemergingissueswithinthedecision-makingframeworkofmanyadolescents.
Inaddition,consumerbehavioroffersexpandedopportunityinado-lescenceaswell.
Transitionbehaviorsaredenedasbehaviorsthatadolescentsuse–eitherovertlyorimplicitly–tosignalimpendingadulthood.
Thesebehaviorsmayhaveotherpurposesaswell,butatleastpartoftheirstatusistosociallyrepresentthetransitionalfeaturesofadolescence.
Someofthosebehaviorsareunhealthy,oratleastsociallypro-scribed.
Examplesincluderiskysexualbehavior,recklessdriving,smoking,drinkingtoexcess,druguse,andcheatingonhomework.
Sometransitionbehaviorsarehealthyandsociallynormative.
Examplesincludeplayingintheschoolband,checkingoutlibrary6JosephLeeRodgersandDavidE.
Bardbooks,playingonatennisteam,andjoiningachurchgroup.
ThereasontheTransitionBehaviorPerspectiveisvaluableinthecontextofthecurrentreviewisthatisorientsattentiontowardbehaviorsthatmanyconsidertobeprototypicaladolescentbehavior.
Mostoftheattentiontotransitionbehaviorsinthesocialscience(andbehaviorgenetic)literatureisonbehaviorsthatwehavepreviouslylabeledmildlyandseverelydeviant(seeRodgers,Billy,&Udry,1984;Rodgers&Rowe,1993).
Whilethesociallyappropriatetransitionbehaviorsdeservemuchmoreattentionthantheyhavereceived,wewillfocusonthosethathavereceivedsubstantialresearchattention.
Thoseincludesmoking,drinking,druguse,anddating/sexualbehavior.
Asecondtheoreticalperspectivehelpsmotivatesomeofthebehaviorgeneticliteratureinthisdomain.
ProblemBehaviorTheory(Jessor&Jessor,1977)suggeststhatanumberofbothmildlyandseverelydeviantbehaviorsmaygrouptogether.
ThequestionofwhetherproblembehaviorsgrouptogetherwasexpandedbyMoft(1993)intoatheoryof"adolescence-limited"versus"life-course-persistent"deviantbehavior.
RodgersandRowe(1990)foundthatsexualbehaviorhadasomewhatunusualstatusinthecontextofProblemBehaviorTheory;whileitdidcovarywithothermildlydeviantbehaviors(e.
g.
,smoking,drinking,anddrivingillegally),italsocontainedsubstantialuniquevarianceofitsownthatdidnotoverlapwiththoseothervariables.
Themethodologyofbehaviorgeneticsprovidesapowerfulapproachtoinvestigatingthisperspective,andwewillreviewseveralstudiesthatconsiderthemultivariaterelationshipsbetweentwoormoreproblembehaviors.
AthirdtheoreticalapproachthatisusefulistheLifeCoursePerspective,whichsuggeststhatnormsareestablishedbysocietytodeneage-appropriatebehavioraltransitions;"agedifferentiationisexpressedinthesequenceofrolesandevents,socialtransitions,andturningpointsthatdepictthelifecourse"(Elder,1975).
HoganandAstone(1986)suggestedthattransitionsfromadolescenceintoandthroughadulthoodhaveorderedstages,andthatsocietyhasnormativeexpectationsaboutage-appropriatelifetransitions;Rindfuss,Swicegood,andRosenfeld(1987)investigateddeviationsfromthosenormativeorderedstages.
MostoftheexamplesofeventsofhighsalienceintheLifeCoursePerspectivearedemographictransitionssuchasmarriage,rstchild,oredu-cation.
IncombiningtheTransitionBehaviorandtheLifeCoursePerspective,webringawholenewdomainofbehaviorsunderthisumbrella.
Inthiscombinedperspective,therstcigarette,therstdrink,andlossofvirginitycanalsobeconsideredtohave"lifecoursestatus,"inthatweorganizeourthinkingandplansinrelationtothetimingoftheseevents.
Further,theyareofparticularsalienceindeningthe"adolescentexperi-ence,"anobservationthatbringsProblemBehaviorTheoryintothisintegrativeframe-work.
Indeed,wesuspectthatmanyindividuals(bothadultsandadolescentsthemselves)woulddenethesemildlyandseverelydeviantbehaviorsascloserto"adolescentproto-typebehaviors"thanthemoresociallynormativetransitionbehaviorslikejoiningclubsandplayingintheband.
Nevertheless,wenotetheexistenceofcertaincognitiveandpersonalitytransitionsthatmayalsobemotivatedbyTransitionBehaviorandLifeCourseperspectives.
CertainsubjectsinschoolmaybeperceivedinaLifeCourseperspective.
Oneexamplewouldbebrightstudentstakingpre-calculusin11thgrade,orAdvancedPlacementEnglishasseniors.
Anotherwouldbethetransitioninjunior-ormid-hightohavingastudyhallBehaviorGeneticsandAdolescentDevelopment7(andassociatedexpectations)aspartoftheschoolexperience.
Athirdwouldbeexpand-ingsocialautonomy,suchasthechoicetoattendaschooldanceortohavelunchoff-campus.
Afourthwouldbetheemergenceofleadershipinahigh-schoolsocial/politicalstructure.
AdolescenceembeddedinahormonalecologyTheideaofadolescent"raginghormones"hasbeenoverplayed;forexample,mostado-lescentsarenotnearlyassexuallyactiveinresponsetothosehormones(eventhosewhoarenonvirginsarenotnearlyassexuallyactive)asmanymediaportrayalsmightsuggest(see,e.
g.
,Rodgers,1996).
Theproperphraseisprobablycloserto"changinghormones.
"Indeed,hormonesdrivemanyofthephysiologicalchangesduringadolescence,whichinturnhavetremendousimpactsonbehavioralprocesses.
Buchanan,Eccles,andBecker(1992)developedanintegratedframeworkinwhichtoviewtheinuencethathormonalchangesduringadolescencehaveonadolescentbehav-iorsandtraits.
TheynotedthatHistorically,mostofthechangesinmoodandbehaviorwerepresumedtobenegativeandtobetheresultofbiologicalfactors,particularlyofhormones.
.
.
.
Morerecently,psychol-ogistshavequestionedboththeprevalenceofsuchnegativechangesandtheirhypothesizedbiologicalroots.
.
.
.
Emphasishasshiftedtocontextual(i.
e.
,family,school,peergroup)andpsychological(i.
e.
,self-esteem,genderroleorientation)factors.
(p.
62)Theirreviewshowshormonalchangestopotentiallyinuenceadolescentself-esteem,happiness,concentration,aggressionandbehaviorproblems,andsocialrelationships.
Udryetal.
(1985)showedalinkbetweenandrogenichormonesandmaleadolescentsexualbehavior,andUdryandTalbert(1988)documentedpersonalityresponsestohormonalchanges.
Susmanetal.
(1985)showedalinkbetweenadolescenthormonelevelsandsocio-emotionalbehaviors.
IntroductorysummaryBehaviorgeneticmodelingtoooftenoccursinitsownvacuum.
Thisintroductionwasdesignedtocreatealargercontextfortheupcomingreviewofbehaviorgeneticstudiesofadolescentbehaviorsandtraits.
Genesinuencehormones.
Hormoneshavebothover-lappingvariancewithandcanchangetraitsandbehaviors.
Alloccuratanorganiclevel,withinanindividualwhoisembeddedinasocialenvironmentoffamily,friends,school,church,andothersocialinuences.
Further,allofthesecomplexinterrelationsaredenedtemporally,andmaymeandifferentthingsatdifferentagesandstages.
TheLifeCourseandTransitionBehaviorPerspectives,alongwithProblemBehaviorTheory,canhelpusappreciatethiscomplexinterplay.
Recentworkinthebehaviorgeneticliteraturehasshiftedourorientationawayfromastrictcausalowfromthegenometobehavior,andhassubstitutedvariouscomplexandfascinatingfeedbackloopsinvolvedinthecausal8JosephLeeRodgersandDavidE.
Bardprocess(see,e.
g.
,Brown,1999;Gottlieb,2000).
Wewillreturntothisbroaderperspec-tiveinaconcludingsection,whereweplaceincontexttheresultsofourreviewofgeneticandenvironmentalinuencesthatemergefromthebehaviorgeneticliterature.
MethodologyUsedinThisReviewToidentifyrelevantempiricalstudiestobereviewedinthischapter,wepartitionedourtitleintothreecomponentkeywords:"behaviorgenetic,""adolescence,"and"develop-ment.
"Ourinitialliteraturereviewidentiedprimaryjournalsineacharea:BehaviorGeneticsfortherst,Adolescenceforthesecond,andDevelopmentalPsychologyforthethird.
Weobtainedcopiesofeacharticlethatinvolvedbehaviorgeneticanalysisofatopicrelatedtoadolescentdevelopmentfrom1985to2000.
Inreviewingthosearticles,weidentiedanumberofadditionalarticlesthatwereobtainedaswell.
Inaddition,severalrecentchaptersinAnnualReviewofPsychologyprovidedbothmaterialandreferencestosupportthisreview(seeMaccoby,2000;Plomin&Rende,1991;Rose,1995;Steinberg&Morris,2001).
ByfarthemajorityofourarticlesreviewedherecomefromBehaviorGeneticsandDevelopmentalPsychology.
Further,mostarerecentarticles.
Thoughwesearchedforrele-vantarticlesineachareabackto1985,mostthatwererelevanthadbeenpublishedmorerecentlythanthat,manyinthelatterhalfofthe1990s.
BehaviorGeneticResearchonAdolescence:TheSocial/BehavioralEcologyThesocial/behavioraldomainsrepresentedwithinthearticleswehavecollectedincludeadolescenttransitionbehaviors(smoking,drinking,sexualbehavior,andotherrisk-takingactivities),social/mentalhealthamongadolescents(includingdepressionandantisocialbehavior),indicatorsofsocialrelationshipswithinthefamily(parentsandsiblings),andtreatmentofcognitiveandpersonalitydevelopmentduringadolescence.
TransitionbehaviorsBehaviorgeneticstudieshaveshownthatthereisgeneticvarianceunderlyingadolescenttransitionbehaviors,andhavealsoindicatedsomeofthedynamicsunderlyingthesocial/environmentalcorrelates.
Whileageneralconsiderationofproblembehaviorsspreadsoutbeyondtheboundariescoveredbytransitionbehavior,theycertainlyoverlapsubstantiallywiththatdomain,especiallythroughalcoholanddruguse.
Withinthedomainofproblembehaviors,Gjoneetal.
(1996)usedtheChildBehav-iorChecklist(CBCL)tomeasureinternalizingandexternalizingproblembehaviorsamongNorwegiansame-sextwinsbornduringthe1970sand1980s.
TheirresultsshowedBehaviorGeneticsandAdolescentDevelopment9signicantheritabilitiesforbothdomains,withincreasingh2anddecreasingc2astheseverityoftheproblembehaviorincreasedforbothinternalizingandexternalizingbehav-iors(althoughrescalingofthosevariablesdampenedthispattern).
VandenOord,Boomsma,andVerhulst(1994)alsousedtheCBCLwithasampleofinternationaladoptedchildrenintheNetherlands.
LikeGjoneetal.
,theyfoundsignicantheritabil-ityforexternalizingbehaviors;however,theydidnotmatchtheirresultforinternalizingbehaviors.
Theyalsofoundlargervarianceformalesthanforfemalesforaggressivebehav-ior,whichtheyspeculatedmighthavegeneticorigins.
Eavesetal.
(1993)studiedconductdisorderitemsfromtheRutterParentQuestionnaireusing8–16-year-oldmaletwinsfromtheVirginiaAdolescentBehavioralDevelopmentstudy.
Theirmodelidentiedfourunderlyinglatentclasses,whichwerethemselvesshowntobeheritable.
However,theirmodelrejectedaunidimensionalinterpretationofthelatentprocessesunderlyingconductdisorder.
Rodgers,Rowe,andLi(1994)studiedmeasuresobtainedfromtheBehavioralProblemIndex(BPI)using5–11-year-oldchildrenfromrespondentsintheNationalLon-gitudinalSurveyofYouth(NLSY),nationallyrepresentativedatafromadolescentsbornbetween1958and1965.
ForthesixsubscalesoftheBPI,theyfoundstrongheritabili-tiesforthemoretrait-basedsubscales(Anxiety,Hyperactivity,andDependent)andweakerheritabilitiesforthesocialsubscales(Antisocial,PeerConict,andHeadstrong).
Further,thethreesocialsubscalesshowedsignicantsharedenvironmentalvariance.
Thequalityofthehomeenvironment(measuredbytheHOME)showedsignicantnon-sharedinuencesonsiblingsinthesamehouseholdforallofthesubscalesexceptforPeerConict.
VanderValketal.
(1998)usedanadoptiondesignwith10–18-year-oldDutchchildrentoinvestigatethelongitudinalstabilityofproblembehaviors.
TheirdependentmeasurescamefromtheChildBehaviorChecklist.
Theyfoundstabilityinanexternal-izingfactor,primarilygeneticinorigin,andmoresharedenvironmentalinuenceattheearlyagesthanatthelaterones.
Rowe,Almeida,andJacobson(1999)studiedadolescentaggressionusingtheAddHealthdata.
Theyfoundanh2=.
32,withlittlesharedenvir-onmentalvariance.
Theheritabilityincreasedfromthisvaluewithincreasesinfamilywarmthmeasuredattheschoollevel.
Finally,vandenOordandRowe(1997)investi-gatedsocialmaladjustmentusingtheBPImeasuresintheNLSY.
Theirndingssuggestedthatnonsharedenvironmentalinuenceshadthemosteffectonchildren'sproblembehav-iors.
Theyalsofoundsupportfora"liabilitymodel,"suggesting"astableunderlyingliabilitymaybethe'thirdvariable'thatexplainstherelationsbetweensubsequentlevelsofproblembehaviors"(pp.
319–320).
Severalstudiesaddressedspecictransitionbehaviors.
Koopmansetal.
(1999)studiedsmokinginitiationandquantityusingatwinstudyofDutchadolescents.
Theytabivari-atemodel,andfoundthattherewereseparatedimensionsunderlyingsmokinginitiationandsmokingquantity.
Theyfoundsubstantialh2=.
39andevengreaterc2=.
54forsmokinginitiation,whileh2andc2becamenegligibleforsmokingquantity.
Thisnding–thatthereareseparate(thoughpotentiallyoverlapping)liabilitiesforsmokingonsetandsmokingpersistence–wasalsoobtainedbyMaddenetal.
(1999)andHeathetal.
(1999)usingadultsamples.
Vikenetal.
(1999)usedtwinsfromaFinnishbirthcohortbornin1975–9tostudyself-reportedalcoholconsumption.
Likethesmokingresultsabove,theyfoundthatsharedenvironmentalinuenceswereimportantindrinkinginitiation,butthatadditivegenetic10JosephLeeRodgersandDavidE.
Bardeffectsbecamemoreimportantinexplainingvarianceindrinkingfrequencyamongthosewhohadalreadybegundrinking.
BusterandRodgers(2000)usedmeasuresoflightandheavydrinkingfromadolescentsintheNLSY.
Theyfoundsignicanth2foradolescentmalesintheNLSYforlightdrinking,withtheshifttosignicantc2forheavydrinking.
Adolescentfemaleshadastronggeneticbasis(andnon-signicantc2's)forbothlightandheavydrinking.
Carey(1992)andMeyerandNeale(1992)usedasimulateddatasettoinvestigateonsetofdruguseamongteenagers.
Careysimulatedthedatasettorepresentthreeprocesses,diffusion/exposure,initialuse,andpersistence.
MeyerandNealetmodelstoshowthat,atleastinthisarticialdataset,thesharedenvironmentaccountedfortwinsimilarityindruguseonsetandtiming.
Whilemultiplestagetheoriesthatincludesocialinuenceprocesseshavebeendevel-opedtoexplainthespreadofadolescenttransitionbehaviorslikesmokinganddrinking(e.
g.
,Rowe&Rodgers,1991;Roweetal.
,1996),thebasicandsimpledistinctionbetweenonsetandmaintenanceappearstobethemostabidingandvaluableonetoemergefromthisinvestigation(e.
g.
,Mayhew,Flay,&Mott,2000).
Thecoherentresultacrossthesestudiesisthatonsetisdrivensocially,butafterinitiationhasoccurred,thevarianceintheamountisgeneticallybased.
Asdiscussedabove,notalltransitionbehaviorsarenecessarilyproblembehaviors.
Participationinsportsisapositivetransitionbehavior(alongwithotherextracurricularactivities,churchprograms,hobbies,etc.
).
Boomsmaetal.
(1989)studiedparticipationinsportsusingteenagedtwinsfromAmsterdamandtheirparents.
Theyfoundageneticcomponenttosportsparticipation,andastrongsharedenvironmentalcomponentforfemales(butnotformales).
Further,theydevelopedabivariatemodelbetweensportsparticipationandheartrate,andfoundheartratetohaveastrongergeneticbasisandsportsparticipationtohaveastrongerenvironmentalbasis.
Weencourageadditionalresearchfallingintothisdomain,inwhichhealthyadolescenttransitionbehaviorsareevaluatedthroughbehaviorgeneticandothermethodologies.
Sexualbehaviorisatransitionbehaviorthatbecomessociallynormativewithincreas-ingage.
Severalbehaviorgeneticstudieshaveidentiedsignicantheritabilitiesformea-suresofage-at-rst-intercourse(e.
g.
,Dunneetal.
,1997;Rodgers,Rowe,&Buster,1999),whichtypicallyoccursduringadolescenceintheculturesstudied.
Milleretal.
(1999)showedarelationshipbetweendopaminereceptorsandageatrstintercourse,provid-inginformationaboutapotentialgeneticmechanismtohelpexplainthislink.
Social/mentalhealthRendeetal.
(1993)tbiometricalmodelstomeasuresofdepressioninadolescents.
Theyfoundasignicantheritabilityintheoveralldepressiondistribution.
However,thegeneticcomponentdisappearedwhenmodelswerettoevaluateextremedepression.
Inotherwords,theredidnotseemtobeanydifferentoradditionalgeneticcomponenttoextremedepressionoverandaboveitsstatusasanextremeformoftheoverallvarianceindepres-sion.
Pikeetal.
(1996)usedUSsiblingpairswhowerewithinfouryearsofoneanotherinage,includingtwins,siblings,half-siblings,andunrelatedsiblings.
DepressionwasBehaviorGeneticsandAdolescentDevelopment11measuredinthreeways,usingtheChildDepressionInventory,theBPI-Depressionsub-scale,andtheBehaviorEventsInventory(BEI).
Theyfoundthatthe"modelattributesthevarianceofdepressivesymptomstosubstantialgeneticinuence,negligiblesharedenvironmentalinuence,andmoderatenonsharedenvironmentalinuence"(p.
597).
Further,theyalsofoundthatmother'snegativitywasassociatedwithadolescentdepres-sionthroughthenonsharedenvironment,independentofgenesandthesharedenviron-ment.
Resultsforfather'snegativityweresimilar.
JacobsonandRowe(1999)usedthekinshipstructureintheNationalLongitudinalSurveyofAdolescentHealth(AddHealth)tostudytherelationbetweensocialconnectednessandadolescentdepression.
Theyfounddifferentmodelsformalesandfemales.
Geneticinuenceswerestrongerforfemalesthanformalesforbothdepressionindicators,andalsoforthecovariationbetweensocialconnectednessanddepression.
Other(overlapping)literaturehasinvestigatedantisocialbehaviorinadolescents.
ThestudybyPikeetal.
(1996)reviewedabovethattreateddepressionalsoinvestigatedanti-socialbehaviorusingsubscalesfromtheBPIandtheBEI.
Antisocialbehaviorshowedmoresharedenvironmentalvariancethandiddepression,butgeneticandnonsharedenvi-ronmentalinuencesalsoaccountedforsignicantvariance.
Aswithdepression,thenon-sharedenvironmentaccountedforcovariationbetweenmother'snegativityandantisocialbehavior,andgeneticandsharedenvironmentalinuencescontributedvarianceaswell.
InastudybyO'Connoretal.
(1998)usingColoradoAdoptionProject(CAP)datafromlatechildhoodandearlyadolescence(ages7–12),antisocialbehaviorwasassessedusingconstructedmeasuresforparentalantisocialbehaviorandtheChildBehaviorChecklist(CBC)forchildren.
Theywereinterestedinthecausaldirectionalityofparentingbehav-iorandchildren'santisocialbehavior.
Theyfoundthatthecovariationbetweennegativeparentingandantisocialbehaviorwasnotevokedbythechild;however,theirresultswereconsistentwithaplausibleparentaleffectonchildren'santisocialbehavior.
Finally,astudybyTopolskietal.
(1997)useddatafromtheVirginiaTwinStudyofAdolescentBehavioralDevelopmenttostudyseparationanxietydisorder(SAD),over-anxiousdisorder,andmanifestanxiety.
Moderateheritabilitieswerefoundforeachofthethree,withmeaningfulsharedenvironmentalvarianceforSAD.
Therewerenostrongageorgenderdifferences.
SocialrelationshipswithfamilymembersTherehasbeensubstantialresearchonadolescentsfromabehaviorgeneticperspectiveonfamilyrelationships.
BoththeTransitionBehaviorandLifeCourseperspectivesprovidemotivationforchangingrelationshipstoemergebetweenadolescentsandtheirfamily.
Becauseadolescentshaveanewandbroaderbehavioralrepertoire,becausetheyarebeginningthetransitionintotheindependenceandautonomyofadulthood,andbecausesocietynotesseveralspecicmarkersduringadolescenceasparticularlysalient(e.
g.
,transitiontohighschool,rstcar,leavinghome,etc.
),thesesocialrelationshipsmaybesubtle,volatile,and/ordynamic.
Inaninterestingmethodologicalstudy,Plominetal.
(1994)showedthatanumberofmeasuresofthefamilyenvironmentinfactcontainsubstantialgeneticvariation:"On12JosephLeeRodgersandDavidE.
Bardaverage,morethanaquarterofthevarianceoftheseenvironmentalmeasurescanbeaccountedforbygeneticdifferencesamongchildren"(p.
32).
Thisstudy,apartoftheNonsharedEnvironmentinAdolescentDevelopment(NEAD)project,recruitedadoles-centsfrombothnon-divorcedandstepfamiliesrandomlychosenfromtheUSpopula-tion.
Thisprojectgrewoutofalargeeffortshowingtheimportanceofnonsharedenvironmentalinuencesonindividualdifferencesinhuman(includingadolescent)behavior.
Thisparticularstudydemonstratedthedifcultyincleanlyseparatingmeasuresintogeneticandenvironmentalcategories.
Elkins,McGue,andIacono(1997)tookadevelopmentalperspectiveinastudyofparent–sonrelationshipsduringadolescence.
TheyusedtheMinnesotaTwinFamilyStudyandaParentalEnvironmentQuestionnairethatassessedvariousaspectsoftheparent–childrelationship.
Theyfounddifferentetiologiesfortwinsaroundage11com-paredtothosearoundage17.
Bothagesshowedheritabilityofadolescents'perceptionsofthequalityofparent–sonrelationships,withsubstantiallyhigherh2fortheoldertwins.
Theseeffectswerestrongerforthefather–sonrelationshipthanforthemother–sonrela-tionship.
Neiderhiseretal.
(1998)useddatafromsame-sexsiblingsintheNEADprojectdescribedabovetostudyadolescentperceptionsofparenting.
Adolescentperceptionsofparentingdidmediateparentconictmeasuresandadolescentantisocialmeasures,andtheassociationbetweenparentalandchildmaladjustmenthadastronggeneticcompo-nent.
Busselletal.
(1999)usedthesamedatasourcetoinvestigatethebasisforthecommonndingthatparent–childrelationshipsarerelatedtothequalityofsiblingrelationships.
Mostofthecovariancebetweenqualityofthemother–childrelationshipandthequalityofthesiblingrelationshipwasattributabletothesharedenvironment,althoughsignicantgeneticandnonsharedenvironmentalcomponentswereidentiedaswell.
Neale(1999)challengedsomeoftheassumptionsfromtheBusselletal.
study,butsupportedthendingoftheimportanceofthesharedenvironmentforbothsiblingandparent–childrelationships(seealsoNeiderhiseretal.
,1999,whorepliedtoNeale'scriticisms).
PersonalityAnumberofresearchershavetbiometricalmodelsbasedonbehaviorgeneticdesignstomeasuresofpersonality.
McGue,Bacon,andLykken(1993)useddatafromtwinsinMinnesotaHighSchoolsduringthe1970s,measuredinlateadolescenceandthenaroundtenyearslater.
TheyusedtheMultidimensionalPersonalityQuestionnaire,whichhassubscalesofpositiveemotionality(similartoextraversion),negativeemotionality(similartoneuroticism/aggression),andconstraint(harmavoidanceandtraditionalism).
Theyfoundreductioningeneticinuenceoverthetwoageperiodsfornegativeemotionality,stabilityinoverallpersonalitystructurethatwasprimarilybasedongeneticprocesses,andchangeinpersonalitystructurethatwasprimarilybasedonenvironmentalfactors.
Billigetal.
(1996)useddatafrom17-year-oldmaletwinsfromtheMinnesotaTwin/FamilyStudywithmeasuresofpersonality(obtainedfromtheMultidimensionalPersonalityQuestionnaire)andasecondsurveycalledLifeEventsInterviewforAdolescents.
Inthissecondinstrument,respondentsindicatedwhichofawidevarietyoflifeeventstheyhadBehaviorGeneticsandAdolescentDevelopment13experienced,whichwerethemselvesdividedintofamilyevents(e.
g.
,thewholefamilymovedintoanewhouse),nonfamilyeventsindependentoftherespondent'sbehavior(e.
g.
,aclosefriendmovedaway),andnonfamilyeventsnotindependentoftherespon-dent'sbehavior(e.
g.
,suspendedfromschool).
Biometricalmodelingshowedageneticbasistononindependentnonfamilylifeeventsandgeneticcovariancebetweennoninde-pendentnonfamilylifeeventsandpersonality(especiallywiththepersonalityfactor,constraint).
Finally,Macaskilletal.
(1994)usedtheEysenckPersonalityScaleswithAus-traliantwinsaged11to18.
Afterpartiallingoutageandgender,theyfoundgeneticinu-enceforpsychoticismandneuroticism.
Othertreatmentofmorespecicpersonalitytopicscanalsobefound.
Koopmansetal.
(1995)studiedsensationseekingusingDutchtwinsaged12–24andtheirparents.
TheyusedZuckerman'sSensationSeekingScale,whichhasseveralnon-overlappingsub-scales.
Theyfoundthat"genesplayamajorroleintheindividualdifferencesinsensationseeking"(p.
354),replicatingresultsfromFulker,Eysenck,andZuckerman.
(1980).
Nosharedenvironmentalinuencesweresignicant.
Eavesetal.
(1997)useda28-itemsocialattitudesurveytostudyconservatism.
Theyfoundanimportantagedifference,withtwinsyoungerthan20havingtheirconservatismrelatedtosharedenvironmentalfactors,whilethoseolderthan20hadconservatismvariancethatwasprimarilyrelatedtogeneticinuence.
CognitiveabilitiesUsinganEgyptiansampleoftwinsaged12–19,Abdel-Rahim,Nagoshi,andVandenberg(1990)studiedmeasuresfromabroadbatteryofcognitivemeasures.
Theyfounddiffer-entresultsfromthoseobtainedfromWesternstudies,withlittledifferencebetweenMZandDZtwinscoresandlowerMZcorrelationsingeneral.
Theyprovideacross-culturalinterpretationofthisresult,althoughtheyhastentonoteseveralmethodologicalconcerns,includinglowsamplesizeandabsenceofheightheritability.
NagoshiandJohnson(1993)usedfamilydatafromtheHawaiiFamilyStudyofCognitionalongwith(age-corrected)measuresofverbalability,spatialability,perceptualspeed,andvisualmemory.
Theyfoundaracedifference(betweenthoseofCaucasianancestryandthoseofJapaneseancestry),withsimilarc2foradolescentsandadults.
PetrilandThompson(1993)usedtwindatafromtheWesternReserveTwinProjectcognitivemeasuresfromtheWISC-R,theColoradoTestofSpecicCognitiveAbilities,theMetropolitanAchievementTest,andtheCognitiveAbilitiesTest.
Univariateanalysisshowedbothgeneticandsharedenvi-ronmentalvarianceunderlyingindividualdifferencesincognitionandachievement,andmultivariateanalysisshowingcovariancebetweenthem(especiallygeneticinuence).
Rodgers,Rowe,andMay(1994)usedPPVT,PIAT,andDigitSpanmeasuresfromchil-drenandthosetransitioningintoadolescents(aged5–12)intheNLSY-Childrendatasettostudyintelligence/achievement.
Theyfoundmoderateh2(medianh2=.
50)andsmallerc2(medianc2=.
16)acrossveabilitymeasures.
Theirparticularfocus,however,wasonthenonsharedenvironmentalinuences.
Theyusedspecicmeasuresofthenonsharedenvironment,includingdifferencesamongsiblingsintripstothemuseum,owningbooks,parentalreading,spanking,andHOMEscores.
Theyfoundasignicantrelationshipof14JosephLeeRodgersandDavidE.
BardbookstothePIATReadingRecognitionsubscale,andasignicantrelationshipoftripstothemuseumtothePIATMathsubscale.
Plominetal.
(1997)usedalongitudinalsampleofColoradoadoptiveandbiologicalchildrentostudybiometricalstabilityacrossages1–16.
Theyfoundthatovertime,chil-drenbecamemoreliketheirparentsincognitiveperformance.
Further,duringadoles-cence,adoptivechildrenbecamesimilartotheirbiologicalparents,suggestingthat"genesthatstablyaffectcognitiveabilitiesinadulthooddonotallcomeintoplayuntiladoles-cence"(p.
442).
Inameta-analysisofliteraturefrom1967–85,McCartney,Harris,andBernieri(1990)foundthattheimportanceofsharedenvironmentasitcontributedtodifferencesinIQdecreasedwithage.
BehaviorGeneticResearchonAdolescence:TheBiological/HormonalEcologyVeryrecently,thehumangenomehasbeenmapped.
Thiseffortstimulatedbothknowl-edgeofandinterestinthewayourhumangeneticstructureinuenceshumanbehavior.
Criticshavelongdecriedeffortstolinkgeneticstructuretobehavioraloutcomes.
Moreproperly,weshouldsimplyunderstandthatgeneticinuenceswillshowupinvirtuallyalldomains.
AsTurkheimer(1998)notes,"Everythingisbiological;everythingisgenetic"(p.
789).
Hedidnotmean,ofcourse,thateverythingisonlygenetic.
Knowledgeofthehumangenomepermitsspecicationofmechanisms.
Specicgeneticlocihavebeenidentiedashavinginuence(inacorrelationalratherthandeter-ministicsense)onanumberofadolescentbehaviorsthathavebeentreatedinthisreview,includingrisk-taking,smoking,andalcoholuse.
Behaviorgeneticsoffersalessdirectindi-catorofgeneticinvolvementthanmoleculargeneticmethods.
Ontheotherhand,theQTL(QuantitativeTraitLoci)methodsimplycorrelatesstructureinthegenomewithmeasuredtraitsofinterest.
Anumberof"falseleads"haveemergedusingQTLstudies,althoughthemethodwillcertainlybevaluableinthelongrun.
Activityinbothmolec-ularandbehavioralgeneticarenashasacceleratedduringthepastdecade,andinmanywaysthetwoapproachescomplementoneanother.
PhysicalgrowthAnumberofbehaviorgeneticstudieshavebeenmadeofadolescentdevelopmentfromabiologicalperspective.
Mostofthesestudieshavetreatedmeasuresofgrowthorotherbiologicalmarkersthatwouldbeexpectedtohavestronggeneticinuences.
Inthesecases,theimportantquestionsareoftenwhetherthereareanyenvironmentalinuencesofnote.
Analysisofweightdevelopmentandweightgainisagoodcaseinpoint.
Whileadultweighthasastrongheritablecomponent(h2equalsaround.
80inonereview;seeGrilo&Pogue-Geile,1991),itseemsreasonablethatenvironmentalinuencemightalsoaffectweight,andmanyofthosemightreasonablyemergefromthefamily.
BehaviorGeneticsandAdolescentDevelopment15JacobsonandRowe(1998)studiedadolescentBodyMassIndex(BMI)amongUSAddHealthrespondentsfromabehaviorgeneticstandpoint.
Theyfoundsubstantialher-itability,consistentwithpreviousstudies,andfoundevidencethatthegenesinuencingBMIaresimilarformalesandfemales.
However,theyfoundsomedifferencesinthegenetic/environmentapportionmentformales/femalesandforblacks/whites.
Further,theyfoundanimportantsourceofsharedenvironmentalinuenceforwhitefemales.
Beunenetal.
(1998)studiedsubcutaneousfatdistributionusingBelgiantwinpairs.
Theymeasuredstature,weight,BMI,andvesubcutaneousskinfoldindicators.
Theyfoundgeneticandnonsharedenvironmentalvariancetounderlieindividualdifferencesinbodyfat,butnosharedenvironmentalinuences.
Theirresultssuggestedthatalloftheskinfoldswereinuencedbythesamesetofgenes.
Anothergrowthprocessisthatrelatedtopuberty.
Studiesofpubertaldevelopmentusingbehaviorgeneticmethodshavebeenconducted,althoughthosewillbereviewedbelowinoursectiononhumanreproduction.
HormonesHarris,Vernon,andBoomsma(1998)studiedtestosteroneinDutchtwin-parentdata.
UnliketheBMIndings,theyfounddifferentgeneticinuencesformalesandfemalesforplasmatestosteroneconcentrations,withheritabilitiesofaroundh2=.
60formalesandh2=.
40forfemales.
Differentgeneticfactorsappearedtoemergeinadulthoodformales,whiletheywerethesameforfemales.
Otherresearchonhormonesthatisnotdirectlytiedtobehaviorgeneticmethodsisneverthelessrelevanttothistreatment.
Udryandhiscolleagues(Udryetal.
,1985;Udry,Talbert,&Morris,1986)showedlinksbetweenandrogensandadolescentsexualbehavioramongbothmalesandfemales.
Sexualbehaviorandhumanreproductionoccurattheboundarybetweensocialandbiologicalprocesses(or,moreproperly,weshouldprobablysaythattheysubstantiallycrosstheboundary).
Thebiologicalmarkersignalingreproductivepotentialispuberty.
DoughtyandRodgers(2000)tbiometricalmodelstomeasuresofageatmenarcheforUSfemaleadolescentsfromtheNLSY.
Theyfoundasignicantandsubstantialheri-tability,withtherestofthevarianceattributabletothenonsharedenvironment/mea-surementerror.
Theyalsofoundthatfatherabsencewasrelatedtoageatmenarche,andingoriginallydevelopedbyBelskyandhiscolleagues(e.
g.
,Belsky,2000)andgivensubstantialattentionintheevolutionarypsychologyliterature.
RodgersandBuster(1994)foundaseasonalcomponenttomenarche,withdisproportionatenumbersofNLSYfemalesreportingrstmenstruationinthesummer.
Further,theyestimatedalargeheritabilityofh2=.
62forseasonalmenarche,andnosharedenvironmentalcomponent.
SexualityandhumanreproductionWehavereviewedseveralstudiesofageatrstintercourseearlierinoursectionontran-sitionbehaviors.
Inaddition,RodgersandDoughty(2000)didabiometricalanalysisofNLSYadolescentfertilityexpectations,fertilityideals,andfertilityoutcomes.
Theyfound16JosephLeeRodgersandDavidE.
Bardasubstantialheritabilityofh2=.
60foridealfertilityreportedatages14–21in1979,althoughtheestimatewasmuchlowerwhenitwasreassessedtwoyearslater.
Moderateheritabilitieswerefoundforlateadolescents(ages17–24in1982)forfertilityexpecta-tions.
ThoughfewoftheNLSYrespondentshadhadchildrenby1982,enoughhaddonesotoestimateheritabilitiesforthiscohortof17–24-year-olds;theyfoundaremarkablyhighh2=.
73,withnosharedenvironmentalvariance.
Obviously,anumberofadoles-centsexualandreproductivebehaviorshavegeneticcomponents,andingthatmightappeartosometobeinconsistentwiththetenetsofFisher'sFundamentalTheoremofNaturalSelection(Fisher,1930).
Thisinconsistencyisonlyapparentandnotreal,however.
Rodgers,Rowe,andMiller(2000)providebroadempiricaltreatmentandRodgersetal.
(2001)discusstheroleofgeneticinuencesonhumantnessandresolvetheapparentinconsistencywithFisher'stheorem,frombothbehaviorgeneticandmoleculargeneticstandpoints.
SummaryStatementsandConclusionBythemselves,behavioralgeneticstudiescanappearsomewhatsterile.
Atoneextreme,suchstudiesoftenreportthe"usualmoderateheritability,"theabsenceofanymeaning-fulsharedenvironment(oratleasttheinterpretablesharedenvironment),muchnon-sharedenvironmentalandmeasurementerror,andlittlebeyond(seeTurkheimer,2000,foraformalizationofthissetofndings).
Butattheotherextreme,theycanidentifyprocessesunderlyinghumanbehavior,suggestinterestingandintricategenetic/environ-mentalinteractions,showinterpretablegenderandracedifferences,complementstudiesfromotherdomains(suchasdevelopmentalpsychology,moleculargenetics,etc.
),andstronglyinformourmodelsofhumanbehavior.
Oneofthestrongestvaluesofbehaviorgeneticmodelingisphilosophical;thisapproachhashelpedtobreakresearchersoutoftheextremeandunhealthytendencytowardsocialdeterminism.
AsPlominandRende(1991)havenoted,behaviorgeneticmodelscanbeaspowerfulforstudyingtheenvi-ronmentasforstudyinggeneticinuences;inthatsense,itisamisnomertocallthissetofmodelsandmethodsbehavior"genetics.
"Thisreviewhasidentiedanumberofcoherentpatternsacrossstudies,whichwillbesummarizedhere.
Geneticinuencesareubiquitousintheadolescentdevelopmentprocess.
Thatstatementisnotsurprisinginregardtoprimarilybiologicaldomainslikepubertaldevelopment,hormones,andphysicaldevelopment.
But,interestingly,theher-itabilitiesformanysocialandbehavioralprocessesaregenerallyofthesamemagnitudeasthoseforthemorebiologicaldomains.
ThisresultstronglysupportsthepositiontakeninRodgers,Rowe,andLi(1994)withregardtostudiesofgeneticorenvironmentalinu-ences:"Eachtypeofinuencecan[i.
e.
,should]becontrolledinthestudyoftheother"(p.
374).
Innosensewouldbehaviorgeneticndingsofgeneticinuenceobviatetheimportanceofdevelopingsocialmodelsofadolescentdevelopment.
Butifthosesocialmodelsdonotcontrolfororotherwiseaccountfortheautomaticsimilarityamongrelatedkincausedbysharedgenes,thenthevalidityofthosendingsisthreatenedataveryfundamentallevel.
BehaviorGeneticsandAdolescentDevelopment17Thisreviewhasalsoidentiedafewsharedenvironmentalinuences,andmanynon-sharedenvironmentalinuences.
TurkheimerandWaldron(2000)evaluatedthestatusofnonsharedenvironmentalinuences,andexpressedpessimismthatwewillidentifyspecicinuencesthathavemuchimportance.
Further,Turkheimer(1999)andMolenaar,Boomsma,andDolan(1997)haveshowntheeffectsoffailingtoaccountforgenetic/environmentalinteractions,whichcanbiasthemanyestimatesofheritabilityandsharedenvironmentalvarianceinstandardbiometricalmodels.
Thesearchisstillonforthespeciccausesofthelargeportionofvariancethatbehaviorgeneticistscall"thenonsharedenvironment.
"Wehavealsospeciedanumberofgenderdifferences,andotherdemographicsub-groupsshowdifferencesingeneticpartitioningaswell.
Inrelationtosexualorrepro-ductivebehaviors,suchdifferencesarevirtuallyaxiomatic.
Inotherdomains,theycanhelpidentifyusefultreatmentapproaches(e.
g.
,inrelationtomentalhealth),usefulinter-ventions(e.
g.
,inrelationtoproblembehaviors),orusefulcomponentsofbehavioralmodelsinbasicresearch.
Weconcludewithsomecommentsaboutthethreetheoreticalperspectiveswehaveusedrepeatedlyinpastresearchtoinformandorganizeourthinking:TransitionBehav-iorTheory,theLifeCoursePerspective,andProblemBehaviorTheory.
BothTransitionBehaviorTheoryandtheLifeCoursePerspectivesuggestthattherearesocialmarkerstowhichadolescentsattendintheirdevelopmentalprocess.
Examplesincludestartinghighschool,therstcigarette,puberty,initiationofsexualbehavior,andbeginningtodrive.
Itseemsclearthatthereisgeneticvarianceunderlyingvirtuallyalloftheindividualdif-ferencesinthesevariousbehaviors.
Somebehaviorandmoleculargeneticresearchreviewedabovehasevenbeenabletoevaluatewhethertherearesharedgeneticinuencescommontothesedifferentdomains.
Infact,weconsiderthatbivariateandmultivariatemodelsshowingthegeneticandenvironmentaloverlapprovidesomeofthemostexcit-ingandvaluablemodelstoapplytofuturekinshipdatausingbehaviorgeneticdesigns.
Anumberofsuchmodelshavebeendevelopedpreviously,andhaveprovidedvaluableandexcitingndings.
Otherswillfollow.
Adolescenceprovidesafascinating"age-gradedlaboratory"forthestudyofdevelop-mentalprocesses.
Behaviorgeneticmethodshavebeenfruitfullyappliedwithinthislaboratory.
Thendingsfromthosestudies,andthewaythosendingsinteractwiththoseoutsidetheboundariesofbehaviorgenetics,haveandwillcontinuetoprovidestimulat-ingandvaluablescience.
KeyReadingsBuster,M.
A.
,&Rodgers,J.
L.
(2000).
Geneticandenvironmentalinuencesonalcoholuse:DFanalysisofNLSYkinshipdata.
JournalofBiosocialScience,32,177–189.
Thisarticleappliesbiometricalmodelingtoadolescentandyoungadultuseofalcohol.
DFanalysisisasimpleregression-basedapproachtoestimatinggeneticandenvironmentalvariancecomponents.
Jacobson,K.
C.
,&Rowe,D.
C.
(1999).
Geneticandenvironmentalinuencesontherelation-shipsbetweenfamilyconnectedness,schoolconnectedness,andadolescentdepressedmood:Sexdifferences.
DevelopmentalPsychology,35(4),926–939.
Thisarticleestimatesbiometricalmodelsforadolescentsrelatingfamily,school,andmentalhealth.
18JosephLeeRodgersandDavidE.
BardMcCartney,K.
,Harris,M.
J.
,&Bernieri,F.
(1990).
Growingupandgrowingapart:Adevelop-mentalmeta-analysisoftwinstudies.
PsychologicalBulletin,107,226–237.
Thisarticleisameta-analysisshowinghowbehaviorgeneticndingsrelatinggeneticandenvi-ronmentalinuencestovariousoutcomesmustbeconditionedontheageoftherespondent.
Itmotivatesthestudyofbehaviorgeneticpatternsinadolescentsaspotentiallydifferentthanforotheragegroups.
Plomin,R.
,&Rende,R.
(1991).
Humanbehavioralgenetics.
InM.
R.
Rosenzweig&L.
W.
Porter(Eds.
),AnnualReviewofPsychology(Vol.
42,pp.
161–190).
PaloAlto,CA:AnnualReviews.
Thisreviewarticleaccountsbroadlyforbiometrical/behaviorgeneticndingsacrossmanydiffer-entdomainsandages.
Rodgers,J.
L.
,Rowe,D.
C.
,&Li,C.
(1994).
Beyondnatureversusnurture:DFanalysisofnonsharedinuencesonproblembehaviors.
DevelopmentalPsychology,30(3),374–384.
Thisarticlegoesbeyondtheusualpartitioningofinuencesingeneticandsharedenvironmentalinuences–amodelisdenedtoaccountexplicitlyformeasured,nonsharedenvironmentalinu-ences.
Themodelisappliedtothestudyofproblembehaviorsinolderchildhoodandyoungado-lescentrespondents.
Turkheimer,E.
(2000).
Threelawsofbehaviorgeneticsandwhattheymean.
CurrentDirectionsinPsychologicalScience,9,160–164.
Thisarticlepresentssomeofthemethodologicalandempiricaldifcultiesofdoingresearchonbehaviorgenetics.
Thecaveatsthatemergeshouldinformallbehaviorgeneticmodelingefforts.
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