Intelligence and giftedness: The contributions of heredity and early environment

Pprron. mrlrruL Dlf Vol II. So. 3. pp. 3’5-316. Pcrgamon Press pk. Pnnted m Great Entam

1991

SPECIAL A neo-Lamarckian

MILES D. STORFER: Intelligence and Gifiedness: Francisco, CA (1990). xxii + 636 pp. 535.00.

REVIEW

theory of the secular rise of intelligence

The Contributions of Heredi1.v and Ear!,

Enrironnrenr. Jossey-Bass.

San

Miles Storfer has written a stimulating synthesis of research studies on intelligence with particular emphasis on the questton of how intelligence can be raised by environmental intervention. Among the many interesting issues discussed in the book, the IWO most important are the analyses of the conditions affecting the development of intelligence in early childhood and of the factors responsible for the increases which have taken place over the course of the present century in the intelligence levels of the populations of the economically developd nations. The book is divided into six parts. The first consists of an overview of the genetic and environmental determinants of intelligence and presents mainstream and generally uncontroversial conclusions. Storfer summarises the twin and adoption studies and concludes that they indicate that approx. 70% of the variance in intelligence is genetically determined. The remaining variance is environmentally determined by two sets of factors. namely intra-uterine effects acting on the foctus and cognitive slimulation efTccts acting on babies and infants. The intra-uterine cfkts consist largely of the adequacy of the nutrition which the foetus receives from the mother and can bc inferred from the well established positive relationship bctwcen birthwcight and intclligcnce which holds even among identical twins. The positive impact of early cognilive stimulation can hc inferred from studies of the effects on intelligcncc of (a) birth order, where first horns tend to receive grcatcr maternal attention and to have higher IQ%; (b) parental age. whcrc older mothers tend IO give greater attention to their chlldrcn and IO have children of higher intclligcnce; (c) family size. where children in smaller families tend to rcceire more attention and to have higher IQ%; and (d) adoption into middle class families which normally provide more attcntlon and which raise the IQ$ of children by around I? IQ points. II is argued that both the quantity and the quality of maternal attention have aJvatl~;~gcous clficts in raising the child’s IQ. Part two of the hook dc;~ls with the prohlcm of the rise of intclligcnce which has been recorded in a numher of counlries over the course of the Prcscnt ccnlury. The magn~~udc of the increase is estimated at 22 IQ points in the Umtcd States and the rate of incrcasc 1s approx. 2.2 IQ poinls per dccadc. About the same rate of incrcasc has been found in several other countries. II is nolrd that the incrcasc has been grcatcr for the visuospatial abilities than for verbal comprehension and vocabulary. Storfcr rcjrcts Flynn’s (19X7) view that the rise in intelligence is an artcfact and dots not reflect genuine incrcascs in mental abililies. llc bclicvcs th3( the rise is genuine and that il has made a significant contribution lo the many rcmarkablc ccicnlilic and technological advances which have taken place in the present century. The causes of the incrc;lses arc considcrcd IO lit in improvcmcnts in social and environmental conditions. We found this ;I well informed and thoroughly senslblc rcvicw :md discussion. The remainder of Part Two deals with the black-white difference in intelligence. II is pointed out that since the black white dilt’crcncc is approx. I5 IQ points, and since the mean IQ in the United States has risen by around 22 IQ points since 1918, thr mean IQ of contemporary blacks must bc higher than that of whites in the early decades of the century is wholly This cannot bc disputed. However. the author argues that this shows that the black-white dilfcrential environmental and this does not follow. The improvements that have taken place in environmental conditions for both blacks and whi[cs has. as Storfcr himself argues, raissd considerably their respective mean IQs. but this does not rule OUI the possibilily of gcnctic dill’crcncrs contributing to the intelligence differences at any one point in time. In a discussion of the causes of the black-white disparity in intelligence. it is argued that about one third of the dilfcrence can bc artributcd to adverse intra-uterine and family contigur~tion factors in blacks arising from the large numbers born IO unmarried teenage girls, who tend to have low birthweight babies and a low level of family support. Thr additional impact of low socio-economic ~131~s can account for almost half the black -white disparity, but no explanation for the rrmainmg half is otTered. The aurhor concludes by wondering why there are so many black teenage stnglr mothers. and raises the question of whsthcr this may not itself have some genetic basis. In his conclusion to this discussion he has apparently changsd his mind about thr cnvironmcntal causation of the black-whlrr IQ ditfercntial and he leaves the possible gcnerlc conrribution to this clltliirential as an open question. Parr Three cxamincs the eKccts of the home environmcnl on the development of intclligcnce in young children. A number of srudics are rcvicwed which Icd the author to conclude that the crucial factors are morhers rocking their infanls. imirllring their vocalisations. gazing 31 them. encouraging attention IO objects and events in the environment. responding promptly IO their ovcrturcs and talking intelligently IO them. Sludies of outstanding individuals and geniuses are reviewed and arc considered IO confirm the thesis thar a high degree of attenlion by mothers IO infants fosters high intelligence in the growing child. ParI Four looks in closer detail at the bcncficial etTects of the cognitive srimulation of infanrs on raising inrclligence. It reviews work by William Fowlcr. Rick Hcbcr and orhcrs claiming that the intensive cognitive training of babies and toddlers mists their intelligence by something of the order of 30 IQ points. II is noted that these enrichment programmes have generally been found IO raise verbal comprehension as measured by the Stanford Binct more than non-verbal problem solving and visuospatial abilities. Storfer is well aware that a number of critics have argued that the cognitive gains made as a result of early enrichment programmcs tend IO fade away after a few years. but he discounts these claims and maintains that the gains are pcrmanenl. He argues that the cognitive stimulation of infants accelcratcs the growth of the dendrites and that this is the neurological basis for its efTectiveness in bringing about a permanent increase in intelligence. As further instances of the cognitive stimulation thesis. chapters are devoted IO the intelligence of the Japanese and the Jews as IWO groups who have some disrinctive high abilities. The Japanese have high visuospatial abilities but weak verbal 323

311

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RE\ IEU

abtllrws. This cqmtlre pattern IS attributed to Japanese mothers’ emphasis on rockq and on the \ISU.II stlmulatwn of their children combined wth a de-emphasis on talklnp to them. wth a consequent failure to develop their herbal abllitws The fact that the s;lme patrern of abllltlrs IS present among the ethmc .Amerlcan Chinese uho have bern resident III rhe Um~sd States for more thdn .I century IS not consldered and may tend to suggest a genrtlc basis to this ahlilt) pdtrrrn. .A contrasting populatwn 13 the Jew. H ho ha\e been found m a number of studies to ha\e htgh genercll mwlllgencr. strong verbal and numerical atnhtles but beaker vlsuospatial abilities. This cognlti\e pattern 1s expressed an JeHlsh dchle\ement. Hhlch has been outstandmg in man) areds of wence but less so m architecture and pdlntlng This pattern IS attrtbuted to Jwlsh child reartng prJctlces uhlch rmphaslse rocking and talking IO infants The author does not considrr the alternatlke theor) of Weyl f 1966) to the effcvt that a long hIstory of persecution has acted as a selection pressure for Increased mtelllgence In the Jeus and that the social mores requtrmg verbally gifted rabbis to ha\e children ha\ been the mu,or factor responsible for the strong Jewtsh herbal ablllttes. The problem raised b> Storfsr’s an~l>s~s of high Japanese \~suospa~~al ability and high Jev.Ish verbal ability is Hhy Japanese and Jeutsh mothers should adopt their partlculdr respective styles of child rearing conducive to fostering these Jbllitles. So doubt Japanese mothers emphaslse visuospdtlal ablhtlcs because they themselves habe s1rong \~suospat~al abllltles. and no doubt they haxe strong blsuospattal .tbllltles because their mothers had them. and so on back doun the generatwns. and con\ersell wth the emphaw of Jeuish mothers on verbal dblllties. We are Inclined to plxc a qucstwn mark wer whether a wholly en\ironmentA explanJtwn can plJustbl> bc maIntained for the strong wsuospattnl ablllttcs of the Japanese and other Oriental and reIdted peoples. including the Chlncse and Eskimos and equalI> for the high general tntslhgence and verbal ability of the Jews. Thus the first four parts of this book are concerned wth ertabllshing the case th,tt the cognitive stImuLItwn of Infants in the first t%o >ears of Ilfe h.is a mayor effect on the development of their mtclligence. This thesis accounts for the enhancement of the intelllgencc of children adopted by mlddle class famllies. for the negative rel,~tionshlp betuecn intelltgence and family six. for the SUKESS of hcadbtart programmes and for much of the secular incrcaw in intelligence during the present centur). It follows 1h.11 If mothers could be given instruction 111the appropriate intelhgcncc raising tcchnqucs-among which rocking IS one of the moot Important-tntelllecnce Icvcls could be raised to much hlghcr lcvcls than those of today.

I’.lrt

f.‘l\e IS conccrncd Hlth the ncuruloplcal and brain mechanisms underlying glftcdne\s. It hcytns uith .I CIexrIptIon \)stcmr idunt~lied as Epiwdlc (memory for evenls), Thematic (I;ICIS org.lnwxl into rchcma1.t) and I low-to hlemq (rsmcmhcrlny hw to do thlngb). Each of thebe kind\ of memory h.ls three Ic\cl\ of permanence. n,rmcly short term memory \rhlch IS yu1cI.1) IOSI (c.g_ for new teiephonc numbers). intermcdxtts or working memory and long term memory where Inl’~~rmatwn IS pcrmanen1l) ~tursd. It 1s ru~gcsrsd that some anlm.ll> with quite small braIn\ hJve well dc~cloped Epl~dlc mcmor~. ?.lany hlrdx hrl\e ewellent spatial memorich for thclr cnvironnwnts. It IS m Thcmatw memory th.11 hum.ln> excel anJ thl> pl.lr an m~port.lnt part in hun1.m intelligence. The rcm.ilnder of this scct~on reiIcH\ m.tn) of the principal nsurophgsioloyical correlates of intclhycnce and oti2rs a \arlct! of spccuI.ItIon\ to c1pl.1111 them. The correlate5 ~ncludr myopia. allerglcs. uric acid Ic\el>. the Gze ofcor1lcal neurones and thslr number of wnncctlons, rc;lctIon tlmss and inqwction times. It is suggested tha1 in glftcd indl\iJual\ neuroncs scr\lng \i\ual an.ll>x~\ h.L\c been rcdcplo>cd IO perform language funs1wns. thereby generatIng a correlation bcr*ecn m~o,p~.~ and bcrh.11 .thihty. E~~rn~n.~~~un of Einstein’s bratn haa revwlcd the prcwnce of large ncuronec with numerous connectwns in the ~swc~at~on cortex of the left hcmlsphcrc (in which lobe IS unspccificd) bu1 not el~whcrc. suggesting that th!s formed the ncuroloylc.tl h.l\l\ of tiln\tc~n’r genius. Rcactwn limes and inspection limes are lntrrprctcd %ismeasures of the rpeed of nourolo+l proccwng unJerl>lng in~clllyencc and necessary hut not sullicient for excepttonal plftcdncss. The scctwn end, ulth wmc qwculativnu conccrnlng the rclarwnship of the two ccrcbral hcmlspheres in whtch It is proposed that m hIghI) glftcd individuals the rlyht and left hemispheres lirst dcbclop their rcspcctibe specialibatlons III spLitid and rerhal an;tl>sis and then bccomc lntcpratcd so tha1 the brain as a whole becomes bilatcraliscd. The speculations on 1hc neuroloylcal proccsws undcrl>ln?: intsll~gncc prcscntrd in this part of 1hc book may provide useful h>pothcscs which call for further cmplrlcal tcs1ing. The SIlth and tins1 part of the hook presents the mw1 novel. arrrstlng and provocat!\c ~dcas which ledd the aurhor IO a nco-Lamarcktan theory of the e\olutlon of intelligence positing 1he inheri1ance of acquired characteristics. The dlscussion which has taken place during the present century. It starts wth a reconsldcratwn of the 22 IQ point rise in intelligence is estlmuted that Improvements in health and nutrition account for about 4 IQ points of thi$ increase, and improbements

of threerncm~~r~

SPECIAL REVIEW

33

in the early environment in which infants are reared (smaller families. more educatIonal toys. parents with more leisure to play wtth 1he1r children. etc.) can explam a further 7 IQ pomts Thus. these tuo factors together can explain about I I of the 22 IQ points mcrease which has taken place. How therefore can the remaminp I1 IQ points of the mcrease be explained? Storfer develops a Lamarckian evolutionary model to account for the rise. hypothesislng that inter-generatIonal changes in the functioning or structure of the genetic system whrch underpins intelligence has been involved. He notes that the speed of the change precludes the Darwinian process of natural selection acting on available genetic variation or nobel mutations. and to save his hypothesis boldly proposes that a Lamarcklan mechanism determmes what he calls ‘intellectual evolution’. According to this notion. when parents acquire a relatively high level of mtelhgence through effort or envIronmental Influences. a process operates whereby developmental changes which habe taken place during the acquisition of their intelhgence are passed on to their children. who then develop a high level of mtelhgence wl1hout having to acquire it. If they in turn acquire a higher level of intelligence than their parents. this is passed on to their children. In this way the mean intelhgence of the population increases from generation to generation much more quickly than would be expected b) traditional evolutionary processes or through environmental changes. The formidable problem which all Lamarckian hypotheses encounter is that there is no known mechanism which enables the DSA of eamctes to be reorganised to reflect changes in somatic cells. in this case the cells of the nervous system. so it is not surprising that such hypotheses have been viewed with scepticism. To resolve the problem. Storfer develops a cornpIe\ model based on his Interpretation of recent Iindlnps in molecular biology. According to the model. the major genetic alteratlons are brought about in the sperm cells of the male. and are changes m the regulatory system which controls gene expression rarher than 1n gene structure pt*r se. Interactions between chohnerglc neurones and the Sertoli cells closely Involved with sprm development. 11 IS argued. mediate the modifications of the regulatory system. most of the process taking place in the dcvelopmentnlly ‘plas1ic‘ pre-pubertal period. This KIGI is certainly inlcrestinp. and If such a process wcrc to be dix-overcd. i1 would be the mos1 important advance in our knowledge ofcvolutwn since the puhllcatlon of the “f/u* Orr,c~~ o/‘.%/x*u~z’. However it is hlphly speculative. and the style in which Storfcr dcvclops 1hc model IS uncomfortably evangelical. The implications of 1hc rcscarch he asscmblcs arc ovcrsratcd and slan~cd toward lus i&as to ;LII unwarranted dcgrce. %luch more concrc1c and unambiguous molecular cvidcnce for the proposed Informa1lonal interplay hc1wccn 1hc nervous and rcproductlhe systems would have to be available bcforc mtnlm.ll crcdcncc could bc glvcn to the model. 1s 1hc rtsc in IQ \corcs sulliclcntly anomalous IO rcquirc a novel cvoluttonary crpl,ln.L1ion? In dcvclopinp his cast. Storfcr is overly d~rrntsslvc of ;~ltcrn;~tlve c~pI;~na~~ons. and doe% IWI sutiiclcntly acknowledge our lack of knowlcdgc ofdcvclopment in hlghcr organlw’\. or the dcvclopncnt (II’ 1n1cll1pcncc tn partlcul.~r. S1;111\1tcalev~dcncc shows that gcnotypc cnvlronment intcrac1ton 1s of crucl;tl Import;lncc 111~hc gcnc~lc .Irchltccturc of lntclllgcncc in 1hc population. yc~ 1hc ways 111which 1hc gcnomc mtcrac1s wi1h cnvIronmcn1;1I Inllucnccs In rhc dcvcloprncnt of Ind1vidu;tl organisms is SIIII larpcly a mystery. To s1udy this prohlcm mc:~nIngfuIIy, WC need more knowlctlgc of how multlccllular phcnotypc’c arc cncodcd and cxprcsscdLnowlcdpc which IS hcing gcncr;ltcd rapIdly wI1h the appllca1ion of rccomhlnant DSA 1cchmquc\. When more IS known of 1hc y~cm by which ncuroncs xuh\crbc ~n~clltgcncc. ant1 of its mschanl\m of dcvclopmcn~. II may hu that the rise in IQ will ml1 po\c much of an anom.~ly . ant1 hhc o1hcr psychologtcal phcnomcna. such ds :dlrui\m. will in the cd lit nc;~tly ill10 Ihc O;IrwIm.in p.lr;itllpni. This new cvolu1lcmary 1hcory rcp~csen~~ such a profound modllicafion of 1hc fundamental principles of gcnc1ic theory th;t1 11amounts IO an a11cmptcd \clcn1llic rcvolutlon In cvalua1iny S1orfcr.s thehI\. we hclwvc it right to apply fhc gcnsral princlplc 1ha1 well c\-t;~bl~~hcd ~CICIIIII‘ICthcorlcs shoultl not he overturned unless thcrc are very compelling reasons for downy 50. In 1hc prcscn1 GM wc d~uh~ uhcthcr .~ny Guch compelling reasons cxzst. The crux of the argumcn1 is that improvcmrn1s in health. nu1rl1lon and early cnvironmcn1aI cond111ons arc only capable of explaining half of ths secular increase !n mtrll~gcnce .~nd 1hcrcIi)rc 111.11II is ncccs\ary 11) posif neo-Lamarckian mechanism, 10 caplain the remaining half. Wc doubt whcthcr 1h13 argumcn1 can he acccp~cd. In our view any supposed increases in 1hc cognitive sttmula!ion o1 young chtldrrn have proh;lhly con1rlbufcd 11111~or nothing to the secular IQ increases, since for the reasons g1vcn earlier we doubt whrrhcr early childhood cognlrtvc s[imuI.ihon has any permanent clrcc1 on mtclhgcnce. Fur1hcrrnore. If mcreases in 1hc cognitive s1lmul;itton of young chlldrcn pl;~yed any appreciable par1 in 1hc secular ribc of Inrclligcnce. the verbal ahlli1les should have rlscn more than the v~suosp;~t~;~lahlhtics because the verbal abilities respond more to cognilivs stlrnul.ltlon. We 1hercfors Jgrcc that mcreases in cognitive s1lmulation. e\cn if thehe could be shown to bc present. cannot c.xplain the secular increahc tin inrslligencc. However. the role of improbemcn1s in nu1rl1lon cannot he dirmisbcd so ligh1ly. Secular Improvcmcn1s in nu1rltion in the economically developed natIons have been considerable over the courbe of this ccn1ur) and have led IO tncreases In hcigh1 and brain si7e of approalmarely 1hc same m.lgnitude as those which have taken pl.~cc in Intclhgcncc. Slorfer d~srn~s~s ~mprovsmon1s in nulrition as having relativclj I111lcclfcc~ on the grounds 1hat thcrc arc onl, low pob111vccorrslarions betuecn height and intelligence. This is a misconception. IIclgh1 and In1clligence are both under Indspcndcn1 ycnc1ic conlrol and this prcvsn1s the appearance of high corrclarions between them. BUI because improkcmcnrs in nutrtllon have brought abou1 consldcrablc increases in hetght and brain size over thr course of the prcscn1 cenlury we consider i1 pl.iusible 1h;k1they hare had a similar c!Tect on intelllgcnce. The argument is set out in de1ail in Lynn (1990) \Vc consldcr 1hls 1hcsis prcfcrable 10 the replacement of 1he well cstabhshed principles of gcncfic theory wirh a nco-Lam.irckian model. AlthtJugh we arc unconkinccd by S1orfer’s two principal theses-the siynlficance attached IO the efTec1sofclrrly childhood s1imularlon on mrclllgcncs and 1he nco-Lamarckian theory of the gcnctic transmission of acquired charac1eristics-we ncvcr1hele>s found much of lntcrcst in 1hl5 hook. Srorfer has amassed a grea1 deal of evidence in suppor1 of his thcorics and his clear cxpoai1ion forces the rcadcr in1o :I careful consideration of the evidence and of possible counter argumenls and aIIerndli\e explanations. Al1hough we arc sccptical about Srorfcr’s maJor theses. this is a book tha1 commands respect and uhich wtll repay a11enrlon by srudcnrs of inrclhgcnce. RICHARD Lrss ROSZIE WILSOS

REFERENCES Clarke. A. hi. & Clarke. A. D. B. (1989). The la1er cognitive effects of early in1erkention. f~~ell~,~cncc*, 13, 289-298. Flynn. J. R. (1987). Massive IQ gains in I4 nations: what IQ tests really mean. Ps~chologico~ Bulkrin. IO/. 171-191.

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Lynn.

R. (1990). The role of nutrition

in the secular

REVIEW

increases

in intelligence.

Personolir~

and hdiciduul

Difewnces.

I/.

273-285.

Plomin. R. (1986). Derelopmenr, generics and psychology. Hillsdale. NJ: Lawrence Erlbaum. Starr. S. & Weinberg. R. A. (1978). The influence of family background on intellectual attainment. Review, 43. 674-692.

Weyl. N. (1966).

7%e creorire

elite in America

Washington.

DC: Public

Affairs

Press.

Ameriron

Sociologiol