Insight into intelligence

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Unformatted text preview: structure of a dodecamer with the intrastrand G—G crosslink in the centre, and the picture is very informative. The double helix is bent towards the major groove by about 45°. This value is in striking agreement with that determined by Crothers and Lippard for cis-platinated DNA by gel electrophoresis”. The central base pairs, including those containing the adjacent G-Cs, are propeller twisted but remain hydrogen bonded. The overall conformation of the duplex changes smoothly but abruptly from the B-form to A—like. This A/B-type hybrid, with its more open and flatter minor groove, may be a recognition element for the HMG- containing proteins. One of the ammine ligands on the platinum forms a hydrogen bond to a phosphate oxygen, which may explain the observed requirement of at least one N-H group for clinically active antitumour compounds. Finally, the plat— inum atom is significantly displaced from the plane of its guanine ligands, a distor- tion that might be relieved when an HMG-domain protein binds. In all, the structure suggests that cis- platin binding to DNA facilitates the con- formational changes that must occur when HMG—domain proteins bind”. Presum— ably (although this is not yet established), the adducts formed by the trans isomer do not have these conformational features. The structural information presented by Takahara et al.1 suggests that other compounds that induce similar structural changes may have antitumour properties. In the rush to find or create such mole- cules, it would be well to remember that the rigid, precise geometries of inorganic and organometallic complexes make them attractive candidates for rational design projects. Van Halen and Metallica fans take note: heavy metal may yet be the wave of the future. Gregory A. Petsko is at the Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachu- setts 02254, USA. 1. Takahara, P. M., Rosenzweig, A, C., Frederick, C. A. & Lippard, S. J. Nature 317, 649—652 (1995). 2. Rosenberg, B, in Nucleic Acid~Metal Ion Interactions (ed. Spiro. T. G.) 1, 1—29 (Wiley, New York, 1980), 3. Werner, A. Z. Anorg. Chem. 3, 267~33O (1893). 4. Comess, K. M. & Lippard. S. J. in Molecular Aspects of Anticancer DrugiflNA Interactions (ed, Neidle, S.) 1, 1347168 (Macmillan, London, 1993), 5. Jantzen, H.-M., Admon, A., Bell, 8. P. & Tjian, R. Nature 344, 830—836 (1990). 6, Huang, J.C., Zamble, D. B., Reardon, J. T., Lippard, S. J. 84 Sancar, A. Proc. natn. Acad. Sci. U.S.A. 91. 10394—10398 (1994). 7. McA’Nulty, M. M. & Lippard, S. J. in Nucleic Acids and Molecular Biology (eds Eckstein. F. & Lilley, D. M. J.) 9, 264—284 (Springer, Berlin, 1995), 8. Sherman, S. E., Gibson, D., Wang, A. H.7J. & Lippard, S. J. Science 230, 412—417 (1985). 9. Admiraal, G. et al. J. Am. chem. Soc. 109, 592—594 (1987). 10. den Hartog. J. H. J. et al. J. biomolec. Struct. Dyn. 2, 1137—1155 (1985). 11. Rice, J. A., Crothers, D. M., Pinto, A. L. & Lippard, S. J. Proc. natn. Acad. Sci. U.S,A. 85, 41584161 (1988). 12. King, C.—Y. & Weiss, M. A. Proc. natn. Acad. Sci, U.S.A. 90, 11990—11994 (1993). NATURE - VOL 377 - 19 OCTOBER 1995 PSYCHOLOGY NEWS AND VIEWS Insight into intelligence Nicholas J. Mackintosh WHAT is intelligence? What does it mean to say that one person is more or less intelligent than another? Are differences in intelligence more or less important than differences in, say, ambition, hard work, ruthlessness, or sheer good fortune in accounting for the success of some and the failure of others? And do IQ tests really measure intelligence — in all or in only some of its aspects? Is it nature or nurture that causes differences in IQ, and how do these causes operate? Do differ— ent groups in our society differ in average IQ, and does this matter? These are seemingly perennial ques— tions , and the fact that they are still being asked suggests a depressing lack of progress. They were very much in evi- dence at a symposium* organized last month under the auspices of the Galton Institute — ironical, considering that many of them were first asked (and confi- dently answered) by Francis Galton him- self more than 100 years ago. On one question at least, participants at the symposium were agreed: IQ has significant, even substantial heritability. A cynic might retort that they would say that, wouldn’t they? But, in truth, the evidence of the past 20 years or so has made an already pretty well established conclusion well-nigh irrefutable. Two studies of separated identical twins pub- lished in the past five years (T. Bouchard, Univ. Minnesota) have reported correla— tions of over 0.70 in their IQ scores; separated non-identical twins resemble one another much less closely. Several adoption studies have found that biologi— cally unrelated people living in the same adoptive family show less resemblance in IQ than biological relatives. To turn a phrase of Leon Kamin (a well known critic of IQ tests) on its head: no prudent person would now accept that the heri- tability of IQ was zero. That question is settled and there are now more interesting questions to ask. Thus we may not know precisely how any genetic effects are mediated, but two con- clusions are emerging. First, some genetic effects are mediated in a very roundabout way via the environment: a particular genetic make—up may predispose someone towards selecting, or fashioning for them— selves, a particular kind of environment that then works back to affect their IQ. Second (as noted by P. McGuffin, Univ. Wales), molecular genetics research has demonstrated that a continuously variable trait (as IQ is) may be influenced by sur- prisingly few genes, with two or three *Sympos/um on Biological and Social Aspects of Intelligence, The Galton Institute, London, UK, 21—22 September 1995. doing most of the work and two or three more completing the picture. No one, of course, is even close to identifying a single major gene with a powerful influ- ence on IQ within the normal range, but this idea may not be in the realm of science fiction. But behaviour genetics has more to say than this. For example, if the heritability of IQ is not much more than 50 per cent, then something like half the variance in IQ can be attributed to environmental factors. But what are these environmental sources of variation? The standard answer has always been family background. Indeed, critics of IQ tests have usually denounced them as thinly disguised mea- sures of conformity to white, middle-class values, and argued that differences in IQ are simply a consequence of the large dif- ference in social, cultural and educational opportunities permitted by an unjust so- ciety. But (as argued by T. Bouchard and by R. Plomin, Inst. of Psychiatry, Univ. London) there is increasing evidence that, as children grow older, so the environ— mental influence of family background on IQ becomes less important. For example, adopted children brought up in the same adoptive family may show a modest resemblance in IQ when they are young, but none at all by the time they are teenagers. The implication is that, by this age, the major source of environmentally induced variance in IQ occurs within fam— ilies, rather than between one family and another. As with many discoveries in social sci- ence, it is easy to remark in retrospect that this is tremendously unsurprising. No doubt. All parents know that they do not treat all their children in the same way. But what is being implied is that it is these differences in individual interaction, prob- ably coupled with experiences that grow- ing children create for themselves outside the family, that eventually exert more influence on IQ than do global measures of family background such as those associ- ated with social class. Behaviour genetics have, paradoxically, probably contributed to our understand- ing of environmental influences on IQ as much as direct studies of the environ- ment itself, which have yielded an ever- lengthening list of factors with small and sometimes only short-lived effects. Only rarely does a study advance our under- standing of how the factor in question exerts its influence. Thus there is evidence (R. Morley, Univ. Cambridge) that infants fed on breast milk rather than formula feeds develop higher IQ scores, but it is not clear what the magic ingredient is, let alone what its more immediate effects are. 581 NEWS AND VIEWS Infectious diseases, parasitic worms or poor nutrition in developing countries (R. Nokes, Univ. Oxford) do not always significantly affect test scores or edu- cational attainment. The only environ— mental factor that seems to have a reasonably large and long-lasting effect on children's IQ scores is adoption into a nice, middle-class family. Of course, adoptive homes represent a rather restricted set of environments: criminals or drunkards are not normally eligible to adopt children, and some people who choose to adopt may be more committed parents than others who, so to speak, have children thrust upon them. Thus it is significant that even within this restricted range, the social class of the adoptive home shows a modest correlation with the adopted child’s IQ — although there are no longi- tudinal data establishing that adoption exerts a long-term effect on children’s test scores. One contentious claim is that various groups differ in average IQ — recently extended to include the two sexes. Francis Galton, like many men of his generation, had no doubt that women were the intel~ lectual inferiors of men. But IQ tests have usually been considered to lend little support to male chauvinism, and the undoubted fact that women tend to have smaller brains than men was attributed to a difference in average body size. More recent examination of this evidence has suggested that this is not true: even when the comparison is between men and women of the same size, women tend to have smaller brains. This, coupled with recent evidence of a significant correla- tion between brain size and IQ, has revived the suggestion that there must be a sex difference in intelligence‘. Whether there really is such a difference may never be answered, for the fact is that while men outscore women on some IQ tests, women outscore men on others, and on some there are no reliable differences worth speaking of. It is obvious enough that different tests must be measuring rather different things. But which is the true measure of intelligence? One answer, of course, is that there is no single true measure of intelligence because there is no single thing called intelligence — only a number of separate, independent abilities“. Most IQ testers acknowledge that there are distinctions between tests of verbal and spatial ability, abstract reasoning and speed of informa- tion processing, but point out, quite correctly, that these tests all correlate positively with one another. It is, there- fore, at best misleading to say that these tests measure wholly independent abili- ties. More plausibly, they measure a set of overlapping processes whose importance varies from one kind of test to another. Whether there is a single, underlying 582 process of general intelligence that is more important than the others is simply not known, and dogmatic pronounce- ments from critics and supporters alike are misplaced. There is no dispute that some groups differ substantially in average scores on Virtually all kinds of IQ test — the most widely publicized example being that between blacks and whites in the United States. Those who study such differences, and have argued that they are probably in part genetically mediated, have sought to defend themselves against a charge of racism by insisting that, in a just society where people are judged as individuals rather than as members of a group, dif- ferences in average IQ between groups would be of no consequence. A forceful counter-argument (J. Flynn, Univ. Otago) is that people do, and are virtually bound to, judge others as members of groups: car insurance companies and police offi— cers take a different View of young males and of middle-aged, respectable females, and if the young male is black, their view will be even more jaundiced. Of course this leads to much injustice but it is also understandable and perhaps even rational: the fact of the matter is that young male drivers are relatively bad insurance risks, and young male blacks commit more crimes than some other sec- tions of society. Viewed from one per- spective, therefore, affirmative action is no more than society’s recompense for other, well-nigh inevitable injustices. One of the theses of The Bell Curve4 was that affirmative action should be abandoned. But the central argument of that widely denounced book was simply that IQ scores matter: whatever IQ tests measure, whether or not they capture everything that everyone might mean by intelligence, IQ does predict educational and occupational success (and much else besides), rather better than the popular alternatives of social class or family back- ground. There is probably a fair measure of truth in this observation. The Bell Curve may be criticized for oversimplification, in particular for frequently falling into the trap of assuming that prediction or corre- lation implies causation. But the sociology of IQ testing will not achieve the maturity now evident in the behaviour genetics of IQ until social scientists start seeking to understand this correlation rather than continuing to wish it away. Nicholas J. Mackintosh is in the Depart- ment of Experimental Psychology, University of Cambridge, Downing Street, Cambridge CB2 3E3, UK. 1. Lynn, R. Person. lndiv. Diff. 17, 2577271 (1994). 2. Gould, S. J. The Mismeasure of Man (Norton, New York, 1981). 3. Gardner, H. Frames of Mind: A Theory of Multiple Intelligence (Basic Books, New York, 1983). 4. Herrnstein, R. J. & Murray, C. The Beli Curve (Free Press, New York, 1994). DAEDALUS Travelling wave IN the popular sport of surf-riding, the rider stands on an exposed board which slides down the face of an advancing wave as fast as the wave itself travels. Much skill is needed to maintain the board’s position on the wave, as it is always in unstable equilibrium. Daedalus once proposed a inverse form of the sport, ‘inverted surfing’. This required a buoyant but submerged board, positioned under the water surface at the back face of the moving wave. It kept pace with the wave from behind, by constantly tending to float up to its crest. It too would be unstable; much skill would be needed to keep it in position. For consistency, felt Daedalus, it should be ridden from beneath by a rider suspended upside down from it and wearing an aqualung. Not surprisingly, inverted surfing never rivalled the conventional variety. But Daedalus now plans to combine the two. A normal surfboard on the front face of a wave, coupled to a inverted board on the back face, should be quite stable. The combination would straddle the wave like a pitched roof, and travel with it dependably, with no need for human skill. Surfers may sneer at such an unsporting craft; but the invention is not aimed at them. Daedalus sees it as an unmanned ocean research vehicle. Without the drag and loading imposed by a human cargo, it could ride not merely the steepened breakers of a shelving beach, but the broader, shallower ocean waves themselves. Daedalus's ‘straddle- surfer’ oceanographic platform will be carried out to sea on a boat, and launched onto a selected wave. It will ride away on it at the typical wave speed of 20—80 km hr‘l, sharing its path and fate. It could relay its position, together with the local temperature, salinity, wind and so on, by satellite radio. When the wave reached shore, maybe thousands of kilometres away, the straddle-surfer would be cast up on the beach. A public- spirited finder might even deliver it to the local coastguards for return to the sender. Straddle-surfers would be so cheap that dozens could be launched together on successive waves as a sort of convoy. The distance between them (measured perhaps by on-board radar or satellite geodesy) would usefully give the wavelength of the swell. A few might lose lock on their waves and be left wallowing, but the rest would travel on. A regular traffic of straddle-surfers might even become a new oceanic resource. Sea-birds could take to riding them, as a more restful form of migration. And those wistful souls who send messages in bottles might turn to small, fast—running straddle-surfers as a form of express post. David Jones NATURE - VOL 377 - 19 OCTOBER 1995 ...
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Insight into intelligence - structure of a dodecamer with...

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