GENDtr,R AND SOCItr,TY EssaysBased on Herbert Spencer LecturesGiven in the (Jniversitv of Oxford. Edited by COLIN BLAKEMORE WaynfleteProfessor of Physiology and Fellow of Magdalen College. SUSAN IVERSEN Professorof Experimental Psychologyand Fellow of Magdalen College. OXTORD UNIVERSITY PRESS OX'FORD IJNIVERSITY PRESS Grcat ClarendonStrce t. Oxford ox: 6ot' Oxford UniversityPress is a departmentof the Universityol Oxford. It furthersthe University'sobjective of excellencein rescarch.scholarship. and educationby publishingworldwide in CONTENTS Oxford Ncw York Athens Auckland Bangkok Bogotii BuenosAires Calcutta CapeTown Chennai Dar es SalaamDelhi FlorenceHong Kong Istanbul Karachi KualaLumpur Madrid MclbourneMexico Citv Munrbai 'laipci 'lbkyo 'lbrottlo Nairobi I)arisSito l)itulo Singapore Warsaw and associatedcompanies in Berlin lbadan List of Figures \rl Oxlord is a registered trademark of Oxford UniversityPrcss in the UK andcertain other countries Vi Publishedin the UnitedStates Lisr of Tables by Oxford University PressInc., New York O the SeveralContributors 2ooo List of Contributors vll The moral rightsof the authorhave been asser(cd Databaseright Oxford University Press(maker) First publishedzooo Sex and Molecular Biology All rightsreserved. No part of thispublication may be reproduced, PETER N. GOODFELLOW storedin a retrievalsystem. or transmitted.in any form or by any means, rvithoutthe prior permissionin writingof Oxford UnivcrsityPre ss, or asexpressly permitted by law,or undcrterms agrecd with the appropriatc Gender and Population r3 reprographicsrights organizations.Enquiries concerning reproduction outsidethe scopeof the aboveshould be sentto the RightsDepartment. SUSAN COTTS WATKINS Oxford Univcrsity Prcss,at the addressabove You mustnot circulatelhis book in any otherbinding ()r cover and you mustimposc the samecondition on any acquiror SexualDifferentiation and CognitiveFunction LUCIA JACOBS BritishLibrary Cataloguing in PublicationData Data available Libraryof CongressCataloging in PublicationData A Little Learning:Womenand (lntellectual)Work 97 Genderand society: the HerbertSpencer lectures / editedby Colin Blakemore, MICHELE LE DOEUFF SusanIversen. Includesbibliographical references and index. t. Sexrole. z. Sexdifferences. 3, Women-Socialconditions. l. Blakemore,Colin. Il. Iversen.Susan D.. 1940- VictimsNo Longer:Feminismand the Reformof HQro75 .G.q6r9:ooo 3o5.3-dczr gg-o'7t9"+ CriminalLaw r r'l ISBN o-t9-1129792<r GERMAINE GREER r3579ro8642 - pesetby Best-setTypesetter Ltd., Hong Kong Printedin Great Britain RaisingDarwin's Consciousness: Sexual Selection on acid-lreepapcr by L J.Intcrnational Ltd andthe PrehominidOrigins of Patriarchy r.+3 Padsto\rCornwall SARAH BLAFFER HRDY Index 20t J SexualDifferentiation and CognitiveFunction LUCIA JACOBS ,l In 1588,Michel de Montaigne concluded, say that male and female are cast in the same mold: save for education and customthe difference betweenthem is not great' [62].If Montaigne could be asked about the relative prop".ii., of men and women in the area not only of morphologv and outward behaviour,but also of cognition I suspecthe *,oulcl give the sameanswer, perhaps more adamantly.yet il is an interestingquestion: how do the sexesdiffer in their percep- tion and processingof information about their external world? And if such differencesexist, do they develop 'education due to and custom',or are cognitivesex diffeiences a consequenceof sexual differentiation? And if such dif- ferences exist, can we supposethat they are functional (i.e. do they occur in other speciesand have they arisenthrough processesof natural selection?). Questions about sex, gender, and cognitive ability are topics of intrinsic and universalinterest, a field of enquirv which hasgenerated tens of thousandsof schorarryarticrei. It is also a field mined with potential political dangersand divisions,and one into which biology vintures at great risk. The firm establishmentof the principles and ramificationsof I would like to thankKim Beenran,Marc Breedrove,John Dark. Kare onstort. Presro'' Margo,wilson, and carol worrhman for helpfuldiscussion otllt*.lf lne ldeas drscussedhere. I rvould also like t;r acknorvledgithe financial supportof the Universityof Californiaat Berkelev. )J Lucia Jacobs Sexualdifferentiation snd cogrtitivefunctiort sexualdifferences, unrelated to culturalcontext, is an impor- functionalexplanation for this sexualdimorphism is that in tant goal,but it lieson the far sideof treacherousintellectual polygynousspecies, males compete amongst themselves for terrain.But we can,at thisjuncture of the expedition,find u..Lrt to females,and thereforerequire proportionately placesto setour feetthat will not leadto disaster.generali- largerbody sizesthan femalesin order to reproduce'In the zationsthat, presumptuousthough they may be, biologists red deer(Cervus elaphtts), for example'larger stags are more feel will survivetheir time and their cultural context.For successfulin defendinga haremof hindsand hencea stag's example,I would arguethat it is a landscapethat must be bodysize is directlyproportional to hisreproductive success understoodwithin a historicalframework. which. to a biolo- Itz]. gist, is the frameworkof evolutionby naturalselection. Despitethe controversy, all would agreethat we haveat least threegood landmarks on which to baseour map.These are: Sexual selection and song first,that in all vertebratespecies, male and femalecognitive abilitiesand brains are more alikethan different;second, that Sexual dimorphisms in body size or antler weight mav suchdifferences can arise through the actionof hormoneson have little to do with cognition,but illustratethe adaptive neuraldevelopment;and third, that the internal environment significanceof sex differences.The boldest and most easilv of the hormonalmilieu is influencedboth by the geneticsof explainedexample of a cognitivesex difference is alsofounc sexdetermination and by the externalenvironment. Hence, in the context of malescompeting for fenralematcs.llris is sexdifferences in the brainand in cognitiveabilities can be the ability of songbirds,also known as passerinebirds. to stronglyinfluenced by the combinedactions of the environ- learn their species-specificsong. Passerinebirds contprise mentand an individual'sgenetic make-up. over half of all bird speciesin the world. and in manv s;recics Using theselandmarks, each discipline constructs its own males must learn to sing [57].These song-learningspecies mapof thisterrain, each perhaps with a distinctivedistortion, show much variability in the timing and tutoring of song: 'View much as SaulSteinberg's 1975 of the World from 9th some specieslearn only at one time period during develop- Avenue'is a tcpclcgicallycorrect but geometricallydistorted ment (criticalperiod or age-limitedlearners) and somelearn representationof the world from the point of view of a New throughout life (open-endedlearners), some learn from a Yorker [Z:]. My route throughthis terrain is basedon the parentand somelearn from surroundingadults. Yet acrossall map of a cognitivepsychologist trained in the pracriceof song learning species,there is a sex difference:males sing ethologyand the rheoryof evolution.I beginwith the bio- more complexsongs than females.Although it is true that in logicalunderpinnings: the distributionof cognitivesex dif- some speciesfemales and malessing duets.where eachpart ferencesin speciesother than our own, and the causesand is of equal complexity,in no speciesdo femaleslearn to sing consequencesof this patternin other species. more complexsongs than males[76]. The puzzleunderlying cognitive sex differences is why sucl, The function of this distinctsex differenceis clear:males a fundamentaltrait as cognitionshould differ oetweenthe require learned song to attract fen:ale mates and to compete sexes.Yet the samecan be saidof even more fundamental againstmale rivals.The ability to learn song is thus subject traits,such as body size.For example,in many polygynous to sexual selection,the selectivepressure rvhich result from mammals.despite similarities in ecologicalniche between competition anong individualsof the same sex h6]. Song malesand females,males are larger than females[4]. The learningability lendsan advantageboth in territory disputes 56 57 Lucia Jacobs Sexualdifferentiation and cognitivcfitnctiort and in female preference:in open-endedlearners, males with its neural basis. The different hormonal milieu of males large song repertoires attract more females.A larg,3rspsl- and females produce sex differences throughout the fine toire is also necessaryfor effective territory defence,because structure of these brain areas (e.g. the volume of brain in many species,the mode of competition among males is regions,the number of neurons,the size of neuronal cell their ability to match the songsof their rivals.Neighbouring bodies, the length of dendrites, and the distribution of males mimic each other's repertoire, song for song, appar- receptors for steroid hormones). Yet if hatchling females ently an efficient method by which they size up each other's are injectedwith the steroidhormone oestrogen,the volume repertoire[8]. Sincerepertoire often increaseswith age,this of song nuclei areas are increasedvia reduced neuronal may providethe listeningbird with someestimate of the com- death and such females rvill both sing and learn sonq petitive characteristicsof his neighbour. syllablesfrom a tutor. If these femalescontinue to receive For these and other reasons,birdsong is considereda sex-