Intelligence_A Very Short Introduction

by Ian J. Deary

  Ulric Neisser, Professor of Psychology at Emory University, was appointed chair. Other members were chosen by an extended consultative process, with the aim of representing a broad range of expertise and opinion, and included nominees from the APA Board on the Advancement of Psychology in the Public Interest, the Committee on Psychological Tests and Assessment and the Council of Representatives. Disputes were resolved by discussion. As a result, the report had the unanimous support of the entire Task Force.

  It is difficult to overestimate the importance of this Task Force for wider communication about the study and understanding of human intelligence differences. Ulric Neisser is one of the best-known research psychologists in the world, the father of ‘cognitive psychology’, the area of psychology that studies mental processes. Much respected, he had not previously been associated with mental testing and was clearly both disinterested and authoritative. On the panel itself was a range of experts one might have expected to argue vigorously and acrimoniously rather than to agree. There were well-known researchers from the field of the genetic–environmental studies of intelligence (Thomas Bouchard and John Loehlin – their work was featured in Chapter 4), and from the more exclusively environmental approach (Stephen Ceci). There were people who took a broader view of intelligence: for example, Nathan Brody, who had dispassionately summarized the area of intelligence difference for fellow academics; and Robert Sternberg, whose theories of intelligence differences go far beyond the typical conceptions of mental ability as encapsulated in IQ tests. There were representatives from the USA’s Educational Testing Service (Gwyneth Boodoo) and people with an interest in the education of minority groups (A. Wade Boykin), in differences between the sexes (Diane Halpern), and in testing as applied to occupational outcomes (Robert Perloff). This was the world’s largest and most influential psychological association knocking some very respected and disparately opinioned heads together and mandating them to come up with a clear, unanimous statement about the knowns and unknowns of human intelligence differences.

  There follows a guide to the contents of the Task Force’s report: I have indicated where it picks up issues raised in this book.

  Concepts of intelligence

  The first topic the Task Force addressed was the key question of what psychologists mean when they study intelligence. They agreed that the word covered many aspects of mental working and their relative efficiency but that

  When two dozen prominent theorists were recently asked to define intelligence, they gave two dozen somewhat different definitions … Such disagreements are not cause for dismay. Scientific research rarely begins with fully agreed definitions, though it may lead to them.

  They did recognize that the main conception of intelligence differences was encapsulated in the so-called psychometric approach. Psychometric means measurement applied to aspects of the mind, and this is the field that tends to be associated with the idea of intelligence testing. As we saw in Chapter 1, tests of mental measurement cover a wide range of mental abilities. In addition, though, the Task Force recognized the part played by conceptions of intelligence that emphasize aspects of mental ability that are not covered by typical IQ-type tests. To repeat, what is tested by mental ability (intelligence) tests is by no means all that human brains are capable of. The Task Force report discusses a wide range of conceptions of intelligence that attempt to go beyond an IQ-type view of mental abilities.

  Intelligence tests and their correlates

  This next section of the Task Force’s report asked whether mental test scores relate to anything else. A scientist may measure some aspect of mental functioning and find that some people score better than others: however, in all honesty he cannot claim that the test scores derive from some prior definition of intelligence. Unlike height or blood pressure, there is no scale from zero to whatever. The measurements of mental ability are not reflecting known aspects of the body’s functioning. The cognitive tasks involved in the intelligence tests might be demonstrably mental, but why should one be interested in them? For three reasons, perhaps.

  First, if the test scores are substantially stable through our lives, then some partly consistent aspect of our mental ability has been reckoned. This was covered in my Chapter 2, and the Task Force report usefully summarizes other research in this area.

  Second, if the tests’ scores can usefully help to predict some aspects of human life that are independent of the test materials, then they have significance that is wider than the surface content. The areas of life in which the tests are applied are work, school, and clinic. These issues are often to do with the tests’ capacity to act as a convenient aid to selection and prediction. The Task Force report discussed in some detail the associations between intelligence test scores and school performance, years of education, job performance, and broader social outcomes such as crime and delinquency. Some aspects of these – mainly selection in the workplace – were described in Chapter 5 of this book.

  Third, there is another aspect of correlates of intelligence test scores to do with where the differences in scores come from. That is, can we discover anything about the brain’s performance that relates to mental test score differences? If this were possible, and if some of the differences in mental test scores were related to aspects of brain processing, then we would be in a better position to understand how the differences in brains produce differences in mental ability. The Task Force’s report discusses how intelligence test scores correlate with components of cognition, reaction time, inspection time, and aspects of neurological function. In Chapter 3 of this book some of these supposedly simpler aspects of brain function that relate to mental test scores were introduced.

  The genes and environment and intelligence

  The APA Task Force’s report considered the evidence for genetic and environmental contributions to differences between people in their mental abilities. Their report goes into more detail and covers more individual studies and topics than was possible in this book (Chapter 4). With regard to the environment, the Task Force agreed that one of the most intriguing findings to emerge in recent years is the generation-upon-generation rise in IQ test scores (discussed here in Chapter 6).

  Group differences in intelligence

  The last topic which the APA’s Task Force addressed was group differences in intelligence. These ‘groups’ were based upon the sexes and ethnic groups. I have not dealt with these topics in the present book and I recommend the Task Force’s treatment of these at times controversial issues.

  I end this summary of the Task Force’s report by listing some of the critical factors that its members believed remain unanswered or mysterious about human intelligence, despite almost a century of research. Here, according to the Task Force’s report, are some of intelligence researchers’ unknowns, some challenges for future research.

  • There is some influence of genes on intelligence, but its exact nature is unknown.

  • The aspects of the environment that affect intelligence are unknown.

  • It is not clear how nutrition affects intelligence.

  • It is not known why intelligence test scores correlate with simpler measures of human performance (see Chapter 3 of this book for examples of these ‘simpler’ measures).

  • There is no satisfactory explanation of why intelligence test scores are increasing with successive generations.

  • The reasons for intelligence test score differences between various groups are not known.

  • There is too little known about the important human abilities that are not tested by intelligence tests (creativity, wisdom, practical sense, social sensitivity).

  To follow this area up…

  I can’t repeat enough that this piece is a must if you want to know more about human intelligence. It is even-handed, well-informed, wide-ranging, and easy to read. This is very definitely the next thing to read on human intelligence.

  Neisser, U. (et al.) (1996). Intelligence: knowns and unknowns. American Psychologis
t, 51, 77–101.

  Further reading

  I hope this Very Short Introduction has stimulated your interest in human intelligence differences. If you want to go further, this section provides some general guidelines. More detail on sources and suggestions for further reading by topic appeared at the end of each chapter in the book.

  Resources on the internet

  The best place to start is the excellent report called ‘Intelligence: knowns and unknowns’ by the American Psychological Association’s Task Force. This is comprehensive, concise, non-technical, and disinterested and tackles controversial topics in a way that is open and sensible. The American Psychological Association’s own summary of this report is available on the world wide web at http://www.apa.org/releases/intell.html and the entire report is available free at http://www.lrainc.com/swtaboo/taboos/apa_01.html. You can also contact the APA’s public office for a copy of the report.

  Another very good summary of the field of research on human intelligence differences was a special issue of the magazine Scientific American Presents. The Winter 1998 edition (volume 9, number 4) was called ‘exploring intelligence’ and had accessible articles on intelligence testing, multiple intelligences, general intelligence, the Bell Curve study, gifted children, the evolution of intelligence, and animal intelligence.

  There’s a free copy of Linda Gottfredson’s article on general intelligence and its importance on the internet at http://www.sciam.com/specialissues/

  1198intelligence/1198gottfred.html. Gottfredson is an able, strong, and persuasive advocate of general intelligence and its practical importance and impact. Her article nicely broadens the work of Hunter that we saw in Chapter 5.

  If you feel you would like some sort of ‘reaction’ to the intelligence orthodoxies I have served up here, I feel a duty to point you toward some intelligence dissenters and sceptics. In the interests of balance, then, Howard Gardner gives a thoughtful account of some key recent issues in intelligence – whether there is more than one type of intelligence, whether intelligence is heritable, and whether emotional intelligence is a valid idea – in an article in the Atlantic Monthly in February 1999, entitled ‘Who owns intelligence?’. He’s the psychologist who wrote the popular Multiple Intelligences. He takes the view that there’s a lot more to intelligence than that which is measured by the sorts of tests I have focused on. You can find it at http://www.theatlantic.com/issues/99feb/intel.html.

  General searches on the internet by title of work or author may lead you to other interesting sites. One further site which I can recommend has many articles on intelligence (history, testing, applications, beyond intelligence). It’s at http://www.sccu.edu/psychology/webintelligence.html.

  Printed resources

  1 Sources for the general reader

  First, I have not laid a great deal of emphasis on introducing what mental test items look like, and I have not knocked up a quick-and-dirty IQ test for this book. If you want more detail on what a test might look like, there are loads of cheap, IQ self-testing books. I should not lay great store on the scores they give or the rank that they put you in. However, at least they offer an inkling of the sorts of mental work some intelligence tests demand. Eysenck (1990) is the one I would recommend.

  Eamon Butler & Masden Pirie. (1983) Test Your IQ. London: Pan.

  Hans J. Eysenck. (1990). Know Your Own IQ. Harmondsworth: Penguin.

  Hans J. Eysenck. (1994). Test Your IQ. London: Thorsons.

  Ken Russell & Phillip Carter. (1999). Test Your IQ. London: Foulsham.

  Most general books on intelligence decry rather than defend the study and applications of intelligence tests. I must be frank: I do not agree with much of the opinion expressed in the three books that follow, but all are well written and make some interesting points. You might as well know the range of opinion that this area of research attracts and you could not do better in getting the critical voice than to read one or more of these.

  Stephen J. Gould. (1997, 2nd edn). The Mismeasure of Man. Harmondsworth: Penguin.

  This is almost entirely critical of the idea of intelligence testing, especially the notion of general intelligence. It’s an odd book, because it has sold very well despite having quite a lot of technical information, about the history of intelligence testing and the statistics involved in mental measurement: it is superbly written. Note that the sections on brain size are out of date and he has refused to correct this despite being sent newly available published data by researchers. People in my research field have severely criticized his account of the statistics of mental measurement. A flawed book, but a great read.

  Michael Howe. (1997). IQ in Question. London: Sage Publications.

  This is an entirely critical account of testing intelligence, genetics and intelligence, applications of intelligence, and group differences in intelligence. Short, clearly written, but a very one-sided book.

  Ken Richardson. (1999). The Making of Intelligence. London: Weidenfeld and Nicolson.

  This energetically points out the flaws in intelligence testing and especially decries studies on the genetics of intelligence, suggesting that intelligence testing should be banned because it is a social evil. Again, this is a one-sided account that makes no disingenuous efforts at ‘balance’.

  We can’t ignore the elephant sitting in the corner, and if you want to be a credible commentator on intelligence’s recent family row it’s worth having a look at The Bell Curve.

  Richard J. Herrnstein & Charles Murray. (1996). The Bell Curve. New York: Free Press.

  Oddly for a book with hundreds of pages of technical, statistical information and calculations, it is extremely easy to understand. The book is a strange mixture. In part it is a thesis about the emergence of a cognitive elite in American society and the danger of a social apartheid based on cognitive ability differences. In part it is a series of analyses of the predictive power of IQ and social class on some of life’s outcomes. The authors certainly wrote some of the clearest accounts of statistical analyses I have ever read, and they communicated widely, selling over half a million copies in the USA. However, the book has spawned volumes and volumes of critical books and articles, amounting to what has been called ‘The Bell Curve Wars’. Just search the internet using the search term ‘Bell Curve’ and you’ll see what I mean.

  2 Sources intended for students

  Colin Cooper. (1999). Intelligence and Abilities. London: Routledge.

  Readable and up to date, Cooper’s book deals with a similar range of topics to that covered in this book, sometimes focusing on different datasets. It has more statistics, and if you want to get more of a handle on the technical issues, this is quite a good, though still selective, introduction.

  N. J. Mackintosh. (1998). IQ and Human Intelligence. Oxford: Oxford University Press.

  A heavyweight, comprehensive account of the topic from the Professor of Psychology at Cambridge University, this book does assume some basic knowledge of statistics, but it is readable and has a stentorian, at times wry and dyspeptic, ‘voice’ commenting on research on intelligence. This is one book used with my students. If you want to get something that is detailed, covers the whole area, and is well written, this is the best book.

  Arthur R. Jensen. (1998). The g Factor. London: Praeger.

  Long, technical, comprehensive, and definitely a book that is on the side of the intelligence tester, this massively well-documented treatise on why general mental ability exists and is important is the book you must visit if you want to know why Gould, Howe, and Richardson (see above) get so worked up.

  Robert J. Sternberg (ed.). (2000). Handbook of Intelligence. Cambridge: Cambridge University Press.

  This is a near-700-page book, covering most aspects of intelligence. Each chapter is written by an acknowledged expert in the area. I have to declare an interest and say that I wrote one of the chapters (on intelligence and simple information processing). The book’s sections are: the nature of intelligence and its measurement; de
velopment of intelligence; group analyses of intelligence; biology of intelligence; intelligence and information processing; kinds of intelligence; testing and teaching intelligence; intelligence, society and culture; intelligence in relation to allied constructs. This is another key book used with my students.

  If you want to get into the general area of the genetic and environmental contributions to human intelligence and other aspects of human psychology, the best book on the market is the following. The authors bend over backwards to make technical material comprehensible.

  Plomin, R. (et al.) (2001, 4th edn). Behavioral Genetics. New York: W. H. Freeman.