PINK BRAIN, BLUE BRAIN The real story of gender difference · 13 13 Ø Sex differences in behavior...
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1 1 PINK BRAIN, BLUE BRAIN The real story of gender difference Lise Eliot, PhD Professor of Neuroscience
Transcript of PINK BRAIN, BLUE BRAIN The real story of gender difference · 13 13 Ø Sex differences in behavior...
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PINKBRAIN,BLUEBRAINTherealstoryofgenderdifference
LiseEliot,PhDProfessorofNeuroscience
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“TheAnchorman”
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Therealstory,in4chapters:
1. Periodiceruptionsofbiologicalsexism
2. Howthebrain&genderdevelop
3. Humanbrainsexdifferencesaresmallandnon-binary
4. Culturealsoshapesthebrain
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Periodiceruptionsofbiologicaljustificationsforgender/STEMstatusquo
Ø Women’ssuffrage– 1920
Ø LarrySummers– 2005
Ø GoogleMemo– 2017
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LettertotheNYTimes,June24,1915
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Sex difference and “The Memo”
• “Possiblenon-biascausesofthegendergapintech”• Citespsychologicaldifferences(people>things;
agreeableness,neuroticism,lowerdriveforstatus)asbasisforlowfemaleattainmentinSTEMandleadership.
• Leapstotheclaimthatthesedifferences“haveclearbiologicalcausesandlinkstoprenataltestosterone.”
• FiredinAug.2017;filedclassactionlawsuitclaimingGooglediscriminatesagainstconservatives,whites,andmen.
• NowregretsthisphotoandsomeofhisearlyAlt-Rightinterviews,butreveredasamartyrinmanycircles.
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“
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buttheyareverysmallandthere’szeroevidencethatthey
,−−−˄
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Biologicaldeterminismiseverywhere……becausesexismissofun!
“Thefemalebrainhastremendousuniqueaptitudes—outstandingverbalagility,theabilitytoconnectdeeplyinfriendship,anearlypsychiccapacitytoreadfacesandtoneofvoiceforemotionsandstatesofmind,andtheabilitytodefuseconflict.Allofthisishardwiredintothebrainsofwomen.Thesearetalentswomenarebornwiththatmanymen,frankly,arenot.”
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Physicalaggressioninyoungchildren
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#ofca
ses
Height
#ofcases
“Empathy”
d=2.6 d=0.35
Genderdifferences:Thedata
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Ø Sexdifferencesinbehaviorarereal,butmuchsmallerthan“Mars/Venus”stereotypesandnotpresentininfancy.
Ø Sexdifferencesarealsopresentatthebrainandbiochemicallevels,butaresmallandenormouslycomplex,notbinary,andnotcurrentlylinkedtoanymale/femalebehavioraldifference.
Ø What’smissingfromthediscussionisdevelopment:Biologicalsex(hormones)mayslightlytiltthings,butalloftheSTEM-relateddifferencesarelargelylearnedthroughpracticeandexperience.
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Ch 2:HOWTHEBRAIN&GENDERDEVELOP
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Howthebraingrowsup
¿ Nature (genes&hormones)andNurture(environment&experience)inextricablyinterwovenfromthefirstcelldivision.
¿ Neuroscientistsusetheterm“plasticity”todescribetheNurtureeffect.Worksaccordingtotwo“activity-dependent” rules:– “Cellsthatfiretogether,wiretogether.”– “Useitorloseit.”
¿ Synapticplasticityisfarmore potentinchildhood&adolescencethanlaterlife.
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Normal rearing
One eye closed
EffectofearlyvisualexperienceHubel & Wiesel (1981 Nobel Prize)
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Synapticpruning&thecriticalperiod
# sy
naps
es
age in years20 40 60 804 8 12 160
visual cortex
Most sensitive phase
End of critical period
frontal lobe
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Criticalperiodforlanguage
(Johnson & Newport, 1989)
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Criticalperiodforgenderdevelopment?Ø Likelanguage,genderlearningbeginsatbirth
(caregiver/culturalimmersionincludingnames,clothes,gesture,expectations).
Ø Byage3,enterthetwo-culturedivideofpeersandin- versusout-groupdynamics.
Ø “Boyculture”promotesvisual-spatialandphysicalskills(plusaggression),while“girlculture”promotesrelational,literacy,andself-regulatoryskills(plusself-objectification).
Ø Inspiteofsomeparents’effortstowardsgreaterneutralitythereisno“gender-free”societyonEarth.
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Kio,age7,identifiesasnon-binary,
prefers“they”
Storm,age5,prefers“she”
Jazz,age10,identifiesas
transgendergirl,“Sexiswhatisbetweenyourlegs,andgenderiswhatyouthinkofyourselfasa
person.”
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Ch 3:SO,WHATIS KNOWNABOUTBRAINSEXDIFFERENCE?Andwhat’sthatgottodowithSTEM?
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Yes,sexinfluences brainstructureandfunction
Ø Psychologicaldifferencestellustheremust besomedifferencesinbrainstructureorfunction.
Ø Butthesmallmagnitudeofbehavioraldifferencesmakesithardtoidentifyreliableneuralcorrelatesinhumans.
Ø Inrodents,thedifferencesaremostdramaticinareascontrollingreproduction.
distribution of estradiol receptors in rat brain
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SexuallyDimorphicNucleus(SDN)ofhypothalamus
◆ INAH-3oftheMPOA:onlystructurewithaprovenvolumedifference
◆ 5Xlargerinmalerats,butonly1.5Xlargerinhumans.
◆ Noclearroleinreproduction,genderidentityorsexualorientation.0.5 mm
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§ Lenroot RKetal.(2007)NeuroImage,36:1065-73.
§ Comparabletotheheightdifference(8.6%),birthweight(9.4%)&otherorgans(e.g.,liver=15%).
Females’brainsare10%smaller&finishgrowingearlier
occipital lobe
parietal lobefrontal lobe
temporal lobeage(years)
volume(m
l)
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Butsexdifferencesinspecificstructuresare“minute”whencorrectedforoverallbrainsize
(n=1143)
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Eta2 =%ofvarianceexplained
(n=865)A=ageS=sex
Sexaccountsfor~1%ofstructuralvariance
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Nosexdifferenceinhippocampusoramygdalavolume(memory,emotion,empathy,aggression)
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Study name Subgroup Mean Age Sample size Hedges's g and 95% CI
Hedges's Males Females g p-Value
Thompson 2008 None 0.0 93 91 -0.074 0.616
Thompson 2009 None 0.0 18 14 -0.514 0.146
Zhang 2012 None 7.3 14 10 0.138 0.729
Tupler 2006 None 11.7 62 60 0.040 0.822
Whittle 2011 None 12.5 58 55 0.279 0.137
Yap 2008 None 12.5 55 51 0.287 0.139
Maller 2007b None 14.5 238 214 -0.250 0.008
Yurgelun-Todd 2003 None 14.6 13 24 0.281 0.406
Nosarti 2002 None 14.9 31 17 1.024 0.001
Head 2004 Young 22.5 26 24 -0.346 0.218
Murphy 1996 Young 25.9 13 11 -2.313 0.000
Narr 2004 None 26.4 30 30 0.216 0.399
Szabo 2003 None 28.0 15 19 -0.473 0.167
Jack 1989 None 30.0 27 25 0.000 1.000
Gao 2012 None 31.3 13 12 -0.784 0.052
Bhatia 1993 None 34.2 15 14 0.000 1.000
Maller 2007a TBV-corrected 37.3 13 17 0.437 0.229
Li 2007 None 37.8 29 32 -0.055 0.829
Bigler 1997 None 40.5 37 59 -0.602 0.005
Goldstein 2002 None 40.5 27 21 -0.214 0.455
Rodrigue 2012 None 54.0 37 76 -0.004 0.986
Maller 2006 TBV-corrected 62.3 76 74 -0.377 0.022
Murphy 1996 Old 70.0 12 12 0.000 1.000
McHugh 2007 None 70.6 12 28 0.134 0.693
Greenberg 2008 None 71.0 16 66 0.000 1.000
Bai 2009 None 71.2 12 11 0.822 0.050
Lloyd 2004 None 73.1 10 29 0.000 1.000
Head 2004 Old 76.5 14 36 -0.159 0.609
Wolf 2004 None 78.7 14 21 -0.087 0.797
1030 1153 -0.063 0.398
-2.00 -1.00 0.00 1.00 2.00
Larger in females Larger in males
A.LeftHCVcorrected(allmethods) B.RightHCVcorrected(allmethods)
Overall
Study name Subgroup Mean Age Sample size Hedges's g and 95% CI
Hedges's Males Females g p-Value
Thompson 2008 None 0.0 93 91 -0.076 0.603
Thompson 2009 None 0.0 18 14 -0.536 0.129
Zhang 2012 None 7.3 14 10 0.111 0.782
Tupler 2006 None 11.7 62 60 -0.163 0.366
Whittle 2011 None 12.5 58 55 0.117 0.532
Yap 2008 None 12.5 55 51 0.140 0.469
Maller 2007b None 14.5 238 214 -0.238 0.012
Yurgelun-Todd 2003 None 14.6 13 24 0.111 0.742
Nosarti 2002 None 14.9 31 17 0.614 0.043
Head 2004 Young 22.5 26 24 -0.275 0.326
Murphy 1996 Young 25.9 13 11 -1.383 0.002
Narr 2004 None 26.4 30 30 -0.215 0.401
Szabo 2003 None 28.0 15 19 -0.670 0.054
Jack 1989 None 30.0 27 25 0.000 1.000
Gao 2012 None 31.3 13 12 -0.467 0.234
Bhatia 1993 None 34.2 15 14 0.000 1.000
Maller 2007a TBV-corrected 37.3 13 17 0.346 0.339
Li 2007 None 37.8 29 32 0.167 0.511
Bigler 1997 None 40.5 37 59 -0.645 0.002
Rodrigue 2012 None 54.0 37 76 0.066 0.742
Maller 2006 TBV-corrected 62.3 76 74 -0.329 0.044
Murphy 1996 Old 70.0 12 12 0.000 1.000
McHugh 2007 None 70.6 12 28 -0.092 0.786
Greenberg 2008 None 71.0 16 66 0.248 0.371
Bai 2009 None 71.2 12 11 0.568 0.167
Lloyd 2004 None 73.1 10 29 0.000 1.000
Head 2004 Old 76.5 14 36 -0.113 0.715
Wolf 2004 None 78.7 14 21 -0.678 0.050
1003 1132 -0.112 0.070
-2.00 -1.00 0.00 1.00 2.00
Larger in females Larger in males
Overall
Largerinfemales LargerinmalesLargerinfemales Largerinmales
Nosexdifferenceinhippocampalvolume
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“Malebrainsappearedtobewiredfronttoback,withfewconnectionsbridgingthetwohemispheres…Infemales,thepathwayscriss-crossed betweenleftandright…Thesedifferencesmightexplainwhymen,ingeneral,tendtobebetteratlearningandperformingasingletask,likecyclingornavigating,whereaswomenaremoreequippedformultitasking.”
ButGoogleNewssayswe’rewireddifferently!
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Neurosexism,2013
“IfVerma andhercolleaguesareright,oneconsequencewouldappeartobetoweakenthecaseforformalorinformalquotasforfemaleparticipationincorporatemanagement,inuniversities,andinfundamentalscience.”
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WhatthePenngroupreallyfound
§ Smalleffectsthatrequirednearly1000subjectstodetect.
§ Nocontrolforbrainsize!!
§ Differenceslargestinmid-adolescence(13-17yrs),comparedtochildhoodandadults,solikelyreflectsatemporarymale-femalematurationaldifference.
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Sameexperiment,controllingforbrainsize
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OTHERMYTHS
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“Mentendtouseonlyonebrainhemisphereata
time,butwomenemploy‘wholebrain’thinking.”
www.girlslearndifferently.com
WRONG, according to meta-analysis: Bishop & Wahlsten (1997) Sex differences in the human corpus callosum: Myth or Reality? Neurosci. & Biobehav. Revs. 21:581-601.
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Wrong:accordingtofMRIlateralizationAugust14,2013DOI:10.1371/journal.pone.0071275
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Butaren’tmenmorelateralizedforlanguage?
Nature(1995),cited1640times
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“NO,”accordingtometa-analysis
I.E.Sommer etal.(2008)Sexdifferencesinhandedness,asymmetryoftheplanumtemporale andfunctionallanguagelateralization.BrainRes., 1206:76-88.
199citations
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AlsoWRONGaccordingtorestingfMRI:Bothmenandwomenarelefthemispheredominant(Liuetal.,n=300)
§ MerrillHiscock:4exhaustivesurveys,1994-2001,inJ.Clin.Exp.Neuropsychologyasking“Isthereasexdifferenceinhumanlaterality?”
§ Founda“weakpopulation-levelsexdifferenceinhemisphericspecialization” forauditory,visual,tactile&dual-taskassays,accountingfor1-2percentofvariance.
§ Similarfindingsinmeta-analysisbyVoyer (1996):0.1%ofvariance.
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Biasand“excesssignificance”inthefMRIcorpus
§ Davidetal.(incl.JohnIoannides)identifiedandanalyzed179fMRIstudiesofsexdifference.
§ Predictedapositivecorrelationbetween#fociofsignificantsexdifferenceandsamplesize.
§ Resultssuggestover-reportingofsexdifferenceinsmallstudies(TypeIerror;falsepositives)andunder-reportingofnon-significanteffects.
predicted
actual
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Sexdifferencesaresexy!
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RestingfMRIactivityfrom1,414participants,35sites:
LE
Smalldifferenceinrestingstateconnectivity
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Andnoneinadolescents
Dosenbach etal.Science,329:1358-61(2010);n=238.
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BrainFallacy
§ Justbecauseasexdifferenceinthebrainis“biological”doesnotmeanitis“hardwired.”
§ Considerthisexperiment:Brainactivationintwodifferentsubjectswhileperformingthesameself-judgmenttask.
§ Genderlearningisatleastaspotentasotherculturalexperienceinshapingbrainfunction.
Han & Northoff (2008) Culture-sensitive neural substrates of human cognition: a transcultural neuroimaging approach. Nature Neuroscience, 9:646-54.
SubjectX
SubjectY
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SUMMARYOFHUMANBRAINSEXDIFFERENCE
§ MRI-baseddifferencesinstructureandactivityaresmallandstatistical(notbinary),requiringverylargepopulationstofindreproducibledifferences.
§ Couldreflect“gender”orsocial-statusasmuchasbiologicalsex(simplyhasnotbeentested!).
§ Noclearcorrelatesofprenataltestosteroneonbrainstructure.
§ Menandwomen’sbrainsarenot“sexuallydimorphic”inthepropersenseoftheterm(e.g.,ovariesvs.testes).
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Ch 4:HOWCULTURESHAPESTHEBRAIN(&GENDERDISPARITIES)
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Sexorstatus?§ Menhavegreaterwealthandpowerineverymodernsociety,somany
male/femalebehavioraldifferencescouldaseasilyderivefromstatusdifferences:– E.g.smiling,empathy,neuroticism
§ Statusdisparitybeginsinchildhood:– Names(“Leslie,Carol,Jordan,
Morgan”)migratefromgirlstoboys,butnevervice-versa.
– Boysexhibitlesscross-genderplaythangirlsduetogreatersocialcost.
– E.g.,“Tonythrowslikeagirl”or“Michaelisagirl”isthegreatestinsulttoboys.
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Socialgenderlearning
• Family,peers,teachers&largerculturedemonstrablyshapechildren’sgenderaspirations:– Toypreference– Motorskills– Mentalrotation– Mathperformance– Verbal,reading,andwritingabilities– Risk-taking– Physicalaggression– Emotionalexpression
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Movement&risk-takingexpectations
• Mothersofgirlsunderestimatedtheslopetheirinfantswouldcrawldown,butmothersofboyswereaccurate.
• Therewasnodifferenceintheactualslopeboysandgirlsdescended.
• Similarstudiesofplaygroundbehaviorfindparentsmoreoftencautiondaughters,butencouragesons’physicalrisk-taking.
Mondschein, Adolph, & Tamis-LeMonda (2000) Gender bias in mothers’ expectations about infant crawling. J. Exp.Child Psychol, 77, 304-316.
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Nosexdifferenceininfantgrossmotormilestones
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Googleprovesparentalgenderbias
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Birthcongratulationcards
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Twonewbooksforkids!
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Gendered crayons
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@CostCo
RealcalculatorToycalculator?
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Crummypinksciencetoys
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http://lettoysbetoys.org.uk/
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Effectofgenderseparation&distinction
§ Decadesofresearchinsocialpsychologyhavedemonstratedthatsegregationpromotesstereotypingandprejudice,whereasintergroupcontactreducesthem.(Pettigrewetal.J.Pers.Soc.Psychol.,90:751,2006)
§ Children,inparticular,learnwhichsocialcategoriesareimportantanddeveloptheirownbiasesaccordingtothewayadultsgrouppeople.
§ See“DevelopmentalIntergroupTheory”(Bigler &Liben,Adv.ChildDev.Behav.,34:39,2006)
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Self-stereotypingbeginsearly:ChildImplicitAssociationTest
“Themath–genderstereotypeisacquiredearlyandinfluencesemergingmathself-conceptspriortoagesatwhichthereareactualdifferencesinmathachievement.”(Cvencek,Meltzoff&Greenwald,ChildDev.,82:766–779,2011)
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Alas,teachersarealsobiased• Whetherweworkwithpreschoolersormedicalstudents,eachofusbringsourexperienceandexpectationsintotheclassroom.
• Experiencetellsusmenandwomenaredifferent,whichunconsciouslytiltsthewayweperceivemalevs.femalestudents.
• Wecanuseknowledgeofgenderdifferencestoeitherreinforce orcounteract stereotypes.
• Thesameistrueforstudentsofcolor,poverty,etc.
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Whenteachersemphasizegender,sodokidsHilliard&Liben(2010)ChildDev.81:1787-98.
§ Artificiallyincreasedgendersalienceforjust2weeksinpreschoolbylabelinggender,separatingbulletinboardsforboysandgirls,groupingbygender,etc.
§ Greaterattentionandmemoryforsamesexplay,rolemodels,etc.
§ Increasedidentificationwithsamegroupandrejectionofout-group.
gend
erflexibility
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§ Atage5,mostboysandgirlsratedmembersoftheirowngenderasboth“brilliant”AND“nice,”butbyages6-7,allchildrenwerelikeliertojudgemalesas“brilliant”andfemalesas“nice.”
§ Ratingsat6-7correlatedwithgreaterselectionofboystoplaygames“forchildrenwhoarereally,reallysmart”(versusnogenderpreferencefor“childrenwhotry really,reallyhard”).
Whogetscalled“brilliant”?
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Meanwhile,themapgaphasdisappeared!
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Internationally,themathgapisalsotrivial
§ Acrossallcountries,themeangenderdifferenceissmall(-0.11<d<0.15)andhasnotablydeclinedinrecentdecades.Varianceratioisalsosmall.
§ Nonetheless,boysreportmorepositivemathattitude(d=0.33).
§ Gendergapsvarywith:1)equityinschoolenrollment,2)women’srepresentationinparliament,3)women’sshareofresearchjobs
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Whatdoesittaketobeasuccessfulscientist/engineer/programmer
• Math,logic,syntax• Self-regulation(organized,focused,disciplined)• Communication(writing,speaking,listening)• Interpersonal(teamwork,empathy,leadership)
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§ Braingenderdifferencesareslightandstatistical,notbinary,andimportantlyshapedbylearningandexperience.
§ Thereisno:“MaleBrain,”or“FemaleBrain”or“GayBrain”or“TransBrain”
§ Genderseparationanddistinctionslimitchildren’sdevelopment...tothedetrimentofbothgirlsand boysandofamoreequal,harmonious,andproductivesociety.
Take-homemessage
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De-biasingstrategies
1. Education
2. Deliberation
3. Accountability
4. Exposuretocounter-stereotypes
5. Reducebiascuesintheenvironment
6. Inter-groupcontact
7. Embracemulti-culturalism(genderdiversity)
8. Perspective-takingexercises
