sphinxxvideos..com

RESEARCHARTICLEDurationofCunnilingusPredictsEstimatedEjaculateVolumeinHumans:aContentAnalysisofPornographyMichaelN.
Pham1&AustinJohnJeffery1&YaelSela1&JustinT.
Lynn2&SaraTrevino2&ZacharyWillockx1&AdamTratner1&PaulItchue1&ToddK.
Shackelford1&BernhardFink3&MelissaM.
McDonald1Publishedonline:10May2016#SpringerInternationalPublishing2016AbstractHumansperformcopulatorybehaviorsthatdonotcontributedirectlytoreproduction(e.
g.
,cunnilingus,prolongedcopulation).
Weconductedacontentanalysisofpornographytoinvestigatewhethersuchbehaviorsmightcontributeindirectlytoreproductionbyinfluencingejaculatevolume—anindicatorofejaculatequality.
Wecoded100pro-fessionalpornographyscenesdepictingthesamemaleactorcopulatingwith100differentfemales,affordingcontrolforbetween-maledifferencesinestimatedejaculatevolume.
Codersvisuallyestimatedejaculatevolumeandrecordedthetimetheactorspentengagedincunnilingus,penile-vaginalpenetration,andinanyphysicalcontactwithhispartner.
Wefoundsupportforthehypothesisthatamanwhospendsmoretimeperformingcunnilingusproducesanejaculatewithgreat-erestimatedvolume,evenaftercontrollingstatisticallyfortheageandattractivenessoftheactress,andtimespentinphysicalcontactwithhispartner.
Additionally,wetestedtheejaculateadjustmenthypothesisforprolongedcopulationandfoundnosupport.
Prolongedcopulationdoesnotfacilitateproductionofanejaculatewithgreaterestimatedvolume,evenaftercon-trollingstatisticallyfortimespentinphysicalcontactwithapartner.
Thisresearchisthefirsttousecontentanalysistodocumentthatpre-ejaculatorycopulatorybehaviorpredictsestimatedejaculatevolumeandalsoisthefirsttodocumentarelationshipbetweenthetimespentperformingcunnilingusandejaculatequality.
KeywordsCunnilingus.
Prolongedcopulation.
Contentanalysis.
Pornography.
Ejaculatevolume"Ejaculatequality"isacompositeofejaculatetraits(e.
g.
,spermmotility,spermviability,spermnumber)thataffectfer-tilizingability(SimmonsandFitzpatrick2012).
Ejaculatevol-umeisanothertraitindicatorofquality.
Forexample,non-spermsubstancesinsemen—whichcomprisethemajorityoftheejaculate'svolume—maypromotefertilizationbypromot-ingspermmotility,reducingtheriskofpreeclampsiaandsup-pressingthefemaleimmuneresponsethatwouldotherwiseattackforeignbodies—includingsperm(BurchandGallup2006;DavisandGallup2006).
AccordingtotheWorldHealthOrganization(WHO2010),lowvolumeejaculatesin-dicateinfertility.
Inhumans,sexualarousalinfluencesejaculatevolumebe-tweenejaculateswithinmen,withgreatersexualarousalas-sociatedwithincreasedejaculatevolumes(WHO2010).
Forexample,menproduceejaculateswithgreatervolumefromcopulation(i.
e.
,morearousing)thanfrommasturbation(i.
e.
,lessarousing;Zavos1985;ZavosandGoodpasture1989),andduringcopulationuninterrupteduntilejaculation(i.
e.
,morearousing)thanduringcoitusinterruptus(i.
e.
,lessarousing;Zavosetal.
1994).
Menproducehigherqualitymasturbatoryejaculateswhentheyspendmore(versusless)timesexuallyaroused(Poundetal.
2002)andwhentheyviewmore(versusless)sexuallyarousingstimuli(KilgallonandSimmons2005;Leiversetal.
2014;Josephetal.
2015).
Menwhoreportgreat-ersexualarousalreportmoreintenseorgasm,moreforcefulejaculation(Phametal.
2013),andproduceanejaculatewithgreatervolume(vanRouenetal.
1996).
*MichaelN.
Phammnpham@oakland.
edu1DepartmentofPsychology,OaklandUniversity,Rochester,MI,USA2DepartmentofPsychology,CaliforniaStateUniversity,Fullerton,CA,USA3InstituteofPsychologyandCourantResearchCenterEvolutionofSocialBehavior,UniversityofGttingen,Gttingen,GermanyEvolutionaryPsychologicalScience(2016)2:220–227DOI10.
1007/s40806-016-0057-5Becausetherearenon-trivialcoststoproducingejaculates(WHO2010),menexperiencegreaterarousalwhentherepro-ductivebenefitsoutweighthecostsofproducingahigherquality,largervolumeejaculate.
Forexample,menaresensi-tivetobehavioral,visual,auditory,andolfactorycuestofe-malefertility(HaseltonandGildersleeve2011).
Menexposedtoawoman'sscentproducedathigh(versuslow)fertilityexperienceatestosteronesurgeandreportgreatersexualin-terest(Dotyetal.
1975;MillerandManer2009;Cerda-Molinaetal.
2013),consistentwiththeideathatmenaresexuallyarousedbyhigh-fertilitycues.
Additionally,menarearousedbycuestospermcompetition;PhamandShackelford(2014)reviewevidencethatmenaresensitivetosociosexual,personality,visual,andolfactorycuestospermcompetition.
Forexample,pornographydepictingtwomenwithawomanismorearousing(Pound2002;McKibbinetal.
2013)andleadsmentoproducemorecompetitivemas-turbatoryejaculatesthanpornographydepictingmultiplewomen(KilgallonandSimmons2005).
Menexposedtospermcompetitioncues(relativetomennotexposedtospermcompetitioncues)reportgreatersexualinterest(Shackelfordetal.
2002,2007;CamilleriandQuinsey2009;PhamandShackelford2013a),greatersexualarousal(Pound2002;McKibbinetal.
2013),andproducehigherqualityejaculates(BakerandBellis1993;KilgallonandSimmons2005;Leiversetal.
2014;Josephetal.
2015).
Thus,menexperiencegreatersexualarousalinsociosexualcircumstances(e.
g.
,higherconceptionrisk,higherspermcompetitionrisk)inwhichthereproductivebenefitsoutweighthecostsofproduc-inghigherquality,greatervolumeejaculates.
Althoughhumansandnon-humansperformsexualbehav-iorsthatdonotcontributedirectlytoreproduction(e.
g.
,cunni-lingus,prolongedcopulation),suchbehaviorsmightcontributeindirectlytoreproduction(e.
g.
,affectingsexualarousalandconsequentejaculatevolume,moreeffectivesemendisplace-ment,increasinglikelihoodoffemaleorgasm).
Sexualarousalfluctuatesduringthecourseofasinglesexualevent(Zavosetal.
1994).
Thecurrentresearchinvestigateswhetherejaculatevolumeispredictedbycunnilingusandbyprolongedcopula-tioninhumans.
Malesofmanymammalianspeciesperformcunnilingusinsociosexualcircumstances(e.
g.
,higherconceptionrisk,higherspermcompetitionrisk)inwhichthereproductiveben-efitsoutweighthecostsofproducinghigherquality,greatervolumeejaculates.
Forexample,malesperformcunnilingustoassessafemale'sfertilitybysniffingandlickinghergenitals(i.
e.
,cunnilingus)togatherscentcuestoherfertilitystatus.
Malecotton-toptamarins(SaguinusOedipus)thatsmellafemale'sscentmarksproducedathighfertility—relativetoatlowfertility—experiencemorefrequentpenileerectionsandperformmoremountingbehaviors(Ziegleretal.
1993).
Gatheringscentcuestofertilitystatusalsomayexplainwhymalesofseveralmammalianspeciesmorefrequentlyperformcunnilingusonhighfertilityfemalesthanonlowfertilityfe-males,includingdogs(Dunbar1977;Kiddyetal.
1978),ham-sters(Mesocricetusauratus:Murphy1973;Johnston1974),bovine(Nishimuraetal.
1991;SankarandArchunan2004),ring-tailedlemurs(Lemurcatta:Palagietal.
2003),andpyg-mymarmosets(Cebuellapygmaea:Soini1987).
MaleIndianflyingfoxes(Pteropusgiganteus)thatspendmoretimeperformingcunnilingusonafemalealsospendmoretimecopulatingwithher(MaruthupandianandMarimuthu2013),andMaruthupandianandMarimuthuhaveinterpretedthisre-lationshipwithrespecttospermcompetitiontheory.
Thus,amongmammals,cunnilingusmayinfluencesexualarousalandconsequentspermcompetitiontactics(e.
g.
,mountingbe-haviors,copulatorythrusting,andejaculateadjustment).
Muchevidencesuggestsanevolutionaryhistoryofcunni-lingusinhumans.
Cunnilingusoccursinmanycultures(e.
g.
,IwawakiandWilson1983;Lurieetal.
1995;Guadamuzetal.
2010),includingpre-industrialcultures(HewlettandHewlett2010),indicatingthatcunnilingusisnotaculture-specificpractice.
Cunnilingusisdepictedfrequentlyinpornography,andpornographyappealstoevolvedmechanisms:Humansdonotpossessadaptationstoexperiencesexualarousalinre-sponsetoviewingcomputerimages,buttoviewing"real-life"humanswithwhomtheycancopulate(Malamuth1996).
Someancestralcavepaintingsdepicthumansengagedinbe-haviorsthatresemblecunnilingus,butAnguloandGarcía(2005)cautionthatthesedepictionsareambiguousand,there-fore,maybeinterpretedinotherways.
Cunnilingusoccursacrossmanyspecies(Soini1987;Nishimuraetal.
1991;Palagietal.
2003;MaruthupandianandMarimuthu2013),andbehaviorsthatoccuracrossspeciesindicatethepossibilityofconvergentadaptations.
Inhumans,menmayperformcunnilingustoincreasetheirsexualarousalandconsequentejaculatevolume,particularlyinsociosexualcircumstances(e.
g.
,highconceptionrisk,highspermcompetitionrisk)inwhichthereproductivebenefitsoutweighthecostsofproducinghigherqualityejaculates.
ThenationallyrepresentativeNationalHealthandSocialLifeSurveyfoundthatwhile71%ofmenfindperformingcunnilinguseitherveryappealingorsomewhatappealing,andonly19%finditnotatallappealing,60%ofwomenfindreceivingcunnilingusveryappealingorsomewhatappealing,and28%reportthatitisnotatallappealing(Laumannetal.
1992),whichsuggeststhatmenmayalsoperformcunnilingustomaketheirpartnermorereceptivetopenile-vaginalsex.
Menwhoreportspendingmoretimeperformingcunnilingusduringtheirmostrecentsexualencounterreportgreatersexualarousalcomparedtotheirtypicalsexualencounters(Phametal.
2013).
Cunnilingusmayalsobemoreoftenemployedincontextsthatpresentgreaterspermcompetitionrisk(reviewedinPhamandShackelford2014).
Menwhoratefemalegenitalodorsthatareproducedduringhighfertility(relativetolowfertility)asmorepleasantsmellingexperienceEvolutionaryPsychologicalScience(2016)2:220–227221atestosteronesurgeandreportgreatersexualinterest(Dotyetal.
1975;Cerda-Molinaetal.
2013).
Menwhoreportspend-ingmoretimeperformingcunnilingusreportgreatersexualarousal(Phametal.
2013),andcunnilingusmayberelatedtoconceptionriskandtospermcompetitionrisk(reviewedinPhamandShackelford2014).
Menwhospendmoretimeperformingcunnilingusmayreceivemoreexposuretocopulins—substancesexcretedbythevaginathatmayin-creasemalesexualarousal(Juette1995).
Mentypicallyper-formcunnilingusbeforetheycopulateandejaculate(HalpernandSherman1979),suggestingthatcunnilingusmayinflu-encesexualarousalandconsequentspermcompetitiontactics(e.
g.
,copulatorythrusting,ejaculateadjustment).
Becausecunnilingusincreasesmalesexualarousalandbecausemalesexualarousaliscorrelatedwithejaculatequality,wehypothesizethatamanwhospendsmoretimeperformingcunnilinguswillproduceanejaculatewithgreatervolume(hypothesis1).
Theejaculateadjustmenthypothesisofprolongedcopula-tionproposesthatmenperformprolongedcopulationstoin-creasetheirsexualarousalandconsequentejaculatequality(Phametal.
2013).
Menwhoreporttheirpartnertobemoresexuallyattractive(and,therefore,presentinggreaterspermcompetitionrisk;Goetzetal.
2005)spendmoretimecopulat-ingatthecouple'snextcopulation(Goetzetal.
2005),andmenwhomasturbatetoimagesofmore(versusless)attractivewomenproducehigherqualityejaculates(Leiversetal.
2014).
Menwhospendmoretimemasturbatingproduceahigherqualityejaculate(Poundetal.
2002).
Thus,prolongedcopu-lationmayincreasesexualarousalandconsequentejaculatevolumeinamannerpredictedbyspermcompetitiontheory(seePhamandShackelford2014).
Thus,wehypothesizethatamanwhospendsmoretimecopulatingwillproduceanejac-ulatewithgreatervolume(hypothesis2).
Humansandnon-humansperformmanybehaviorsduringasinglecopulatoryevent(e.
g.
,touching,kissing),eachofwhichmayaffectmalesexualarousalandcopulatorybehav-iors.
Forexample,batsthatspendmoretimeperformingfel-latio(Cynopterussphinx;Tanetal.
2009)orcunnilingus(Pteropusgiganteus;MaruthupandianandMarimuthu2013)spendmoretimecopulating,andsimilarrelationshipshavebeendocumentedinhumans(Phametal.
2013).
Therefore,intestsofthehypotheses,wecontrolstatisticallyforthetotaltimetheperformersspendinphysicalcontact.
Wealsocontrolstatisticallyfortheactress'sageandattrac-tiveness—eachofwhichisacuetofemalefertility(Buss1989)—becausemalesadjusttheirejaculatequalityasafunc-tiontotheirsexualpartner'sfertility(Goetzetal.
2005;Leiversetal.
2014).
Inparticular,wefocusonbodyattractive-nessbecausebodyattractiveness(morethanfaceattractive-ness)providesinformationaboutawoman'scurrentfertility(Conferetal.
2010).
Indeed,menprioritizebodyattractive-ness(overfaceattractiveness)whenselectingshort-termmatingpartners(Conferetal.
2010;CurrieandLittle2009)—theverymatingcontextthatpornographydepicts.
Previousstudiesonhumansthatassesstherelationshipbetweensexualbehaviorandejaculatequalityreliedonindi-rectmeasuresofsexualbehaviortoprotectparticipantprivacy(e.
g.
,researchersmeasurethetimeparticipantsspendinaprivateroomtoindirectlyassessthetimetheyspendmastur-bating:Poundetal.
2002;participantsself-reportwhethertheyejaculatedviamasturbationorviacopulation:Dehghanietal.
2004).
Toaddresstheselimitations,wetestedthehypothesesbysecuringmoredirectmeasuresofsexualbehaviors:Usingcontentanalysisofprofession-alpornographyscenes,codersassessedthetimethemaleactorspentperformingcunnilingusandperformingvagi-nalpenetration,thetotaltimethepartnersspentinphys-icalcontact,andvisuallyestimatedejaculatevolume.
MethodWeconductedacontentanalysisofprofessionalpornographyscenes.
Weimplementedfiveinclusioncriteriaforselectingpornographyscenesforanalysis.
First,weincludedonlyscenesdepictingonemanhavingsexwithonewomanbe-causethenumberandsexofperformersaffectejaculatequal-ity(KilgallonandSimmons2005).
Second,weincludedonlyscenesinwhichthecamerapresentedaclearviewoftheejaculate.
Thiscriterionexcludedscenesinwhichejaculationoccurredeitherinsidethewomanoroutsidethecamera'sview,orinwhichnoejaculationoccurred.
Third,becauseejaculatevolumevariesbetweenmen(WHO2010),wese-lectedonlyscenesstarringthesamemaleactor.
WeusedInternetAdultFilmDatabase(IAFD.
com)—awebsitecon-tainingbiographicalinformationforover100,000adultper-formers(IAFD2015)—toverifythatthesamemaleactorwasdepictedacrossalltheselectedscenes.
Fourth,weincludedonlyscenesthatbeganbeforeperformersmadephysicalcon-tactandthatendedafterejaculation.
Fifth,weincludedonlyscenesinwhichthemandidnotwearacondombecausecondomsaffectsexualarousal(seeMacDonaldetal.
2000).
Wesearchedwebsitesprovidingfreeaccesstopornography:keezmovies.
com,pornhub.
com,xnxx.
com,xhamster.
com,youporn.
com,andxvideos.
com.
WeusedIAFD.
comtoen-surethateachscenedepictedadifferentactressandthatallscenesdepictedthesameactor.
Sixcoders(twowomen,fourmen)codedatotalof100scenes.
Allcoderswereblindtothehypotheses.
Fiveofthesixcodersindependentlyestimatedthevolumeoftheejaculate(inteaspoons),andtwoofthesixcodersrecordedthenumberofsecondstheperformersspentengagedincunnilingus,vaginalpenetration,andanyphysicalcontact.
Multiplestarttimesandstoptimesweredocumentedwhenbehaviorsoccurredmorethanonceinascene(e.
g.
,actorperformedcunnilingus,then222EvolutionaryPsychologicalScience(2016)2:220–227performedvaginalpenetration,thenresumedcunnilingus),andthedurationoftheseactivitieswassummediftheyoc-curredpriortoejaculation.
Coderswereinstructedtoestimatethetotalejaculatevolumebyobservingthenumberandquan-tityofeachejaculatoryspurt,startingfromwhentheejaculateleftthepenisuntilitappearedafterlanding.
Eachcoderpro-videdoneestimateofejaculatevolume.
Ninesceneswereexcludedbecausetheycouldnotbecodedforallvariablesduetomissingdata(e.
g.
,sceneswereremovedfromwebsitesduringthedatacollectionperiod),leaving91scenesforanalyses.
Wesecuredratingsofeachactress'sbodyattractivenessfrompornstarnetwork.
com—amega-sitecontaining56por-nographywebsitesand11,300pornographyscenes(PornstarNetwork2015).
Userssubmitbodyattractivenessratingsofindividualactressesona10-pointsystem(1=horrible,10=perfect).
Thewebsitedisplaysaverageratingsofeachactressbasedonhundredsofuser-submittedratings.
UsingdatawecollectedfromtheInternetAdultFilmDatabase(IAFD.
com),werecordedtheyearinwhicheachactresswasbornandtheyearinwhichherscenewasreleased.
ResultsWeconstructedanestimatedejaculatevolumevariablefromthemeanoftheestimatesofejaculatevolume(α=0.
78).
Weconstructedthreetimevariables(anyphysicalcontact,cunni-lingus,penile-vaginalpenetration)fromthemeansofthees-timatesofeachofthosevariables(α=0.
95,0.
84,and0.
91,respectively).
UsingdatafromAIFD,wecalculatedeachactress'sagebysubtractingtheyearinwhichthescenewasreleasedfromtheyearinwhichtheactressinthatscenewasborn.
Weuseddatasecuredfrompornstarnetwork.
comtomeasureeachactress'sbodyattractiveness.
Table1presentsdescriptivestatisticsandzero-ordercorre-lationsamongthekeyvariables.
Totestthehypothesisthatamanwhospendsmoretimeperformingcunnilinguswillpro-duceanejaculatewithgreaterestimatedvolume(hypothesis1),weconductedahierarchicalmultipleregression(seeTable2).
Instep1,weenteredtheageandattractivenessoftheactressandthetimespentinanyphysicalcontact(aftersubtractingfromthisvariablethetimespentperformingcunnilingus)topredictestimatedejaculatevolume.
Instep2,weaddedthetimespentperformingcunnilingusintothemodel.
Consistentwithhypothesis1,whentheactorspentmoretimeperformingcunnilingus,heproducedanejaculatewithgreateresti-matedvolume(β=0.
27,t=2.
32,p<0.
05).
Totestthenormalityassumptionoflinearregression,weconductedKolmogorov-SmirnovandShapiro-Wilktestsonthere-sidualsofthismodel.
Bothtestsyieldednon-significantresults,indicatingthatnormalityassumptionsweremet:D(85)=0.
06,p=0.
20;S-W(85)=0.
98,p=0.
25.
Totesttheejaculateadjustmenthypothesisforprolongedcopulation(hypotheses2),weconductedahierarchicalmulti-pleregression(seeTable3).
Instep1,weenteredtheageandattractivenessoftheactressandthetimespentinanyphysicalcontact(aftersubtractingfromthisvariablethetimespentperformingvaginalpenetration).
Instep2,weaddedthetimespentperformingvaginalpenetrationintothemodel.
Resultswereinconsistentwithhypothesis2.
Whentheactorspentmoretimeperformingvaginalpenetration,hedidnotproduceanejaculatewithgreaterestimatedvolume(β=0.
03,t=0.
25,p=0.
80).
Totestthenormalityassumptionoflinearregression,weconductedKolmogorov-SmirnovandShapiro-Wilktestsontheresidualsofthismodel.
Bothtestsyieldednon-significantresults,indicatingthatnormalityassumptionsweremet:D(89)=0.
07,p=0.
20;S-W(89)=0.
98,p=0.
34.
Becauseofprofessionalvideoediting,somesceneshadinterruptions.
Althoughtheseeditslikelyremovedbehaviorsthatwereirrelevanttoourhypotheses(e.
g.
,editingouttimesduringwhichperformersreadjustedorchangedpositions),sucheditingmayhaveresultedininaccuratecodingofthetargetvariables.
Therefore,weconductedaseparatesetofanalysesinwhichweexcludedallscenesthatcontainedvideo-editedinterruptionsduringsexualactivity.
Afterapply-ingthisexclusioncriterion,weconductedthesameanalysesdescribedabove.
Hypothesis1remainedsupported(n=68,β=0.
33,t=2.
53,p<0.
05),andhypothesis2remainedunsup-ported(n=68,β=0.
06,t=0.
41,p=0.
69).
DiscussionTheresultsofthecurrentresearchsupportthehypothesisthatamanwhospendsmoretimeperformingcunnilinguspro-ducesanejaculatewithgreaterestimatedvolume(hypothesis1),evenaftercontrollingforpotentialconfounds,includingthetotaltimetheperformersspentinphysicalcontactandtheageandattractivenessoftheactress.
Wedidnotfindsupportforthehypothesisthatamanwhospendsmoretimecopulat-ingwillproduceanejaculatewithgreaterestimatedvolume(hypothesis2).
Thecurrentresearchisthefirsttodocumentarelationshipbetweenthetimespentperformingcunnilingusandejaculatequality.
Analternativehypothesisforprolongedcopulationisthatmenperformprolongedcopulationstospendmoretimedisplacingrivalsementhatmaybeinawoman'sreproductivetract(Goetzetal.
2005).
Gallupetal.
(2003)usedartificialgenitalsandartificialsemenandprovidedevidencethattheshapeofthehumanpenisfacilitatessemendisplacementfromthevaginaduringcopulatorythrusting.
Goetzetal.
(2005)foundthatmenwhoperceivetheirpartnertobemoreattrac-tive(i.
e.
,presentinggreaterspermcompetitionrisk)performmoresemendisplacementcopulatorybehaviors(e.
g.
,deeper,morevigorouscopulatorythrusts),includingprolongedEvolutionaryPsychologicalScience(2016)2:220–227223copulations.
Althoughtheresultsofthecurrentresearchdidnotsupporttheejaculateadjustmenthypothesisforprolongedcopulation,futureresearchcanextendtheresultsofGoetzetal.
byconductingacontentanalysisofamateurpornogra-phytoassesswhethermenwhocopulatewithamoreattrac-tivewomanalsospendmoretimecopulatingwithher.
Thecurrentresearchisguidedbyamaleperspectivebe-causemalesexualarousalmediatestherelationshipbetweencopulatorybehaviorsandejaculatequality.
However,womenplaysignificantrolesincopulatorybehavior.
Forexample,menperformcunnilingustosatisfyawoman(PhamandShackelford2013b),oftenuponherrequest(Backstrometal.
2012),andwomencandeterminethedurationofcopu-lationdependingonthesexualposition(e.
g.
,whenawomanismountedontopofaman).
Womenalsohavereproductiveinterestsintheirpartner'sejaculatequality.
Whenwomen'sinterestsandmen'sinterestsarealigned(i.
e.
,sexualcoopera-tion),womenmaybenefitfromtheirpartner'shigherqualityejaculate(e.
g.
,whenacoupleisattemptingtoconceive).
Thus,theresultsofthecurrentresearchshouldbeinterpretednotastheexclusiveproductofamalestrategy,butinsteadastheproductofmaleandfemalesexualstrategiesthatarevariablyinconflictorcooperation(seeShackelfordandGoetz2012).
Professionalpornography—incontrastwithamateurpor-nography—usessuperiorcameraworkand,therefore,produceshigherqualityvideoofejaculations.
However,producersanddirectorsofprofessionalpornographymaydictatethetimepro-fessionalactorsspendperformingsexualbehaviors.
Thus,thedurationofsexualbehaviorsinprofessionalpornographymaynotaccuratelyreflectthedurationofthesebehaviorsinnormal,naturalcircumstances.
Furthermore,havingsexpubliclyinexchangeforpaymentfromviewers(i.
e.
,professionalpornography)likelydidnotoccurinancestralenviron-ments.
Peoplemightperformdifferentsexualbehaviorsinamateurpornographythaninprofessionalpornography.
However,becauseejaculateadjustmentisanautonomicreflex—unconsciouslycontrolledbythemalesexualre-sponsecycle(JonesandLopez2013)—therelationshipsbetweensexualbehaviorsandestimatedejaculatevolumedocumentedinthecurrentresearchmightbegeneralizabletonormal,naturalcircumstances.
Nevertheless,futureTable1Zero-ordercorrelationsamongkeyvariables(n=85)MeanSD123451Estimatedejaculatevolume2.
48teaspoons0.
642Physicalcontact1437.
11s375.
360.
023Cunnilingus87.
14s97.
380.
210.
41**4Penile-vaginalpenetration689.
33s324.
690.
020.
21*0.
32**5Age25.
56years6.
500.
080.
120.
26*0.
006Attractiveness9.
141.
070.
040.
030.
200.
060.
04*p<.
05and**p<.
01Table2Hierarchicalmultipleregressionanalysisassessingtherelationshipbetweenthetimespentperformingcunnilingusandestimatedejaculatevolume,controllingstatisticallyforthetotaltimespentinphysicalcontactandtheageandattractivenessoftheactressβS.
E.
tpvalueStep1(r2=0.
01)Age0.
070.
010.
670.
50Attractiveness0.
030.
060.
310.
76Physicalcontact0.
070.
000.
660.
51Step2(r2=0.
08)Cunnilingus0.
270.
002.
320.
02Age0.
140.
011.
270.
21Attractiveness0.
030.
060.
230.
82Physicalcontact0.
120.
001.
120.
26βstandardizedbetacoefficient,S.
E.
standarderrorofβ,tteststatisticassociatedwithβTable3Hierarchicalmultipleregressionanalysisassessingtherelationshipbetweenthetimespentperformingpenile-vaginalpenetrationandestimatedejaculatevolume,controllingstatisticallyforthetotaltimespentinphysicalcontactandtheageandattractivenessoftheactressβS.
E.
tpvalueStep1(r2=0.
01)Age0.
010.
010.
910.
36Bodyattractiveness0.
040.
060.
340.
74Physicalcontact0.
020.
000.
190.
85Step2(r2=0.
01)Penile-vaginalpenetration0.
030.
000.
250.
80Age0.
100.
010.
880.
38Bodyattractiveness0.
040.
060.
340.
73Physicalcontact0.
040.
000.
290.
77Westandardizedthetargetvariablesbeforeconductingmultipleregressionβstandardizedbetacoefficient,S.
E.
standarderrorofβ,tteststatisticassociatedwithβ224EvolutionaryPsychologicalScience(2016)2:220–227researchmightattempttoreplicateresultsofthecurrentresearchusingcontentanalysesofamateurpornography.
Alimitationofthecurrentresearchisrelianceonvisualestimatesratherthanactualassessmentsofejaculatevolume.
However,ourhypotheses(e.
g.
,timespentperformingcunni-lingusispositivelycorrelatedwithejaculatevolume)dependonlyonreliableestimatesofvolume—notontheaccuracyofejaculatevolumeestimates.
Inotherwords,itisirrelevantwhethercoderscorrectlyidentifiedejaculatevolumesintea-spoons,onlythattheycorrectlyidentifiedtherelativediffer-encesinejaculatevolumesbetweenscenes.
Theindependentcodersachievedreasonableinter-rateragreementinestimatingejaculatevolume(α=0.
78),indicatingthattheseestimatescanbemadewithsufficientreliabilitytowarrantinclusioninempiricalanalyses.
Nevertheless,futureresearchcouldsecuremotioncapturevideoofparticipantsduringcopulationtodi-rectlymeasuresexualbehaviorandcouldcollecttheejaculate(e.
g.
,viacondom)producedfromthatcopulationtodirectlymeasureejaculatevolume.
Additionally,wecodedscenesinwhichthemanejac-ulatedoutsidethevagina.
Suchejaculationsdonotresultinfertilizationsand,therefore,representnon-adaptiveen-counters.
Indeed,menproducelowerqualityejaculateswhentheywithdrawtheirpenisfromthevaginaimmedi-atelypriortoejaculation(Zavosetal.
1994).
Futurere-searchcanemployfluorescentdyesinwhichresearcherscanmeasureejaculatevolumeinsidethefemalereproduc-tivetract,amethodologythathasbeenusedinnon-humanresearchmeasuringthefertilizingsuccessofejaculates(e.
g.
,Lymberyetal.
2016).
Wecouldnotdeterminewhentheactorlastejaculatedbe-foreeachscene.
Thismayexplainwhythetworegressionmodelsaccountedforasmallpercentageofthevariance:Thedurationofabstinenceisconsistentlyoneofthestrongestpredictorsofejaculatevolume(WHO2010).
Indeed,instud-iesthatinvestigatethestrategicadjustmentsinejaculatequal-ity,participantsareinstructedtoabstainforatleast48hpriortosubmittingtheirejaculatesforanalysis(Josephetal.
2015;KilgallonandSimmons.
2005;Leiversetal.
2014)Futurereplicationsofthecurrentresearchcouldsecureinformationaboutthemostrecentejaculationpriortoeachcopulationtoincreasetheexplanatorypowerofthemodels.
Additionally,thesmalleffectsizemaybeattributabletothehumanolfactorysystem.
Humansarelessdependentonchemosensorysystemsthanareotherprimates(Giladetal.
2003).
Therelationshipbetweencunnilingusandejaculatequalityinhumansmayberemnantsofadaptationsfoundinspeciescloselyrelatedtohumans(i.
e.
,otherprimates).
Ifthisisthecase,thenweexpectmuchstrongereffectsizeswhenreplicatingthecurrentresearchtonon-humanprimates.
Thequalityofmen'smasturbatoryejaculatesaredependentonseveralfeaturesofthepornographytheyconsume,includ-ingcuestospermcompetition(KilgallonandSimmons2005)andtheactress'smatevalue(Leiversetal.
2014).
Futurere-searchcouldextendourfindingsbyinvestigatingwhethermenproducedifferentqualityejaculatesdependingonwheth-ercunnilingusisdepictedinthepornographytheyconsume.
Variationinqualitybetweenejaculateshasbeenhistorical-lyinterpretedbyandrologistsas"noise,"withtheWHO(2010)recommendingthatclinicianssecuretwoorthreeejac-ulatesfromamantodeterminehis"true"fertility.
However,agrowingbodyofresearchindicatesthatmenstrategicallyad-justtheirejaculates(reviewedinPhamandShackelford2014)—includingadjustmentsinnon-spermchemicalsthataffectfertilizingsuccess(BurchandGallup2006;DavisandGallup2006).
Thecurrentresearchcontributestothislitera-turebydocumentingthatmen'spre-ejaculatorysexualbehav-iormayaffectejaculatequality.
Further,thecurrentresearchcontributesdatafromhumanstothesubstantialnon-humanliteraturedocumentingthatcopulatorybehaviorsthatdonotcontributedirectlytoreproductioncontributeindirectlytoreproductionbyaffectingsexualarousalandconsequentejaculatequality.
Finally,thecurrentresearchisthefirsttodocumentarelationshipbetweenthetimespentperformingcunnilingusandejaculatequality.
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