Some questions about intelligence are hard to answer, at least for scientists. Are people more intelligent than animals? Will machines soon be more intelligent than people? Is good intelligence necessary for office work, for obtaining a university degree, for organising a modern family holiday, for enjoying any art that is worthy of the name, or for harnessing creatively the deeper human instincts and impulses? Or might society organize such matters so that no great intelligence was required? Could 'intelligence' retain whatever is its usual meaning if it were sharply distinguished - as some say it must be - from whatever IQ tests measure?
These are fascinating questions about intelligence; but they do not look answerable at present. For example, what tests of abilities could provide a fair method of comparison between people and animals? Humans do not fly, echo-locate or navigate by built-in magnetic compasses; and even man's closest fellow-primates do not have the capacity for propositional thought that human language provides. Assuming that intelligence is not just some general 'capacity to adapt' (which might be attributed loosely to virtually any species - cf Schull et al., 1990), it must have evolved (when it did) against the background of the radically different sensory worlds and ecological requirements of different species (see Candland, 1993, for full consideration). Recent primate research has provided a new appreciation of the capacity of apes to learn arbitrary symbols and interact with humans (Marler, 1995); but such communication is not assisted by a grammar that highlights agency and the sequencing of events. Because of such differences in faculties between species, virtually any intended test of intelligence would be 'biassed' except when the species to be compared were closely related. It is thus no wonder that Mackintosh (1988) should think that "the central task of a comparative psychology of intelligence is....to analyse the idea of intelligence - to the point where we can probably dispense with it entirely." For the 'intelligence' differences that distinguish homo sapiens from other mammals might simply turn out to be different principally in quality from those that distinguish eagles from other birds, whales from mammals or pigs from other farmyard animals; and such an observation would rule out any useful talk of all the differences involving any single characteristic of 'intelligence'.
Human-computer comparisons are similarly problematic. Computers 'crunch' supplied numbers impressively; whereas people possess knowledge of a wide environment - and of its dangers and its opportunities for them. No current robot would have a conventional, all-round IQ as high as 2 without the help of a human guide, interpreter and button-pusher; yet a computer allowed a human operator of mediocre intelligence would easily do far better on some tests - for example, if arithmetical operations, spelling or the provision of common synonyms were required. The point is that fair comparison is only possible when the various 'testees' - whether people or animals or computers - can all make a start with the types of problem that are to be set, and when the tests sample the range of activities that the testees might be said to undertake intelligently. Animal intelligence cannot be gainsaid because of lack of symbol use; and computer intelligence cannot be proved by superlative performance at chess. Yet to assess a person's intelligence without examining symbol use or to assess a computer's abilities without considering speed of information processing would be equally unfair and strangely neglectful of important capacities.
Questions involving species comparisons cannot be answered until there are sensible and systematic ways of comparing species. Other questions about intelligence, however, are hard to answer even for man alone; and even the best-thought-out definition of intelligence cannot be guaranteed to prevail over future empirical discoveries and social changes. To work out and establish tests for a new concept of intelligence that was unrelated to IQ would require a discovery of correlations between mental abilities that had escaped the notice of IQ's many critics for almost a century. Any such 'new IQ' would have to be expressed in a wide range of tests and tricks that correlated with each other, but not with the 'old' IQ tests. Yet such a huge change might just be conceivable as people work increasingly in tandem with computers and word-processors and differ in their adjustments to changing social expectations. Abilities summarised as 'computer literacy', 'skill at virtual reality games', 'social sensitivity' or even 'political correctness' might replace IQ testing in future - just as IQ tests themselves once replaced knowledge of Latin, Greek and English grammar as publicly usable criteria of people's employability. If a society encourages the performance of certain rituals - whether demonstration of familiarity with the works of Jacques Derrida, or the scrupulous avoidance of wearing ties - supposedly intelligent people will presumably be over-represented among the first to grasp what are the latest local requirements for ease of passage and socio-economic success.
Some of the above questions will doubtless be answered one day; and this book is intended provide some pointers - though the very latest apparent yardsticks of intelligence will always invite controversy. Meanwhile, however, there are four main questions about intelligence that do seem to border on being answerable in the present. It is these more manageable, yet still contested questions that are the concern of this book - just as they have been the concern of psychologists throughout the twentieth century.
- Are there general intellectual differences between people which affect most mental abilities and which can be reliably and fairly 'measured' by current psychometric techniques?
- If individual differences in 'general intelligence'(g ) can be identified and assessed, what is known of g's essential nature - of the underlying psychological mechanisms and processes that yield the conspicuous differences in test-scores and everyday abilities?
- How do such measured g differences arise developmentally between people - from genetic and/or environmental sources and their psychogenetic interplay?
- Must g differences be considered to be of psychotelic importance to people's individual personalities, attainments, life chances and responsiveness to educational provision - perhaps suggesting some biosocial purpose, function or survival-value?
The four chapters of the book deal in turn with these four questions. Such questions - about psychometrics, psychology, psychogenetics and psychotelics - are the four classic questions of differential psychology: they can be asked in principle about any proposed 'dimension' of personality, ability, motivation or belief.
More limited as these four questions might seem than questions about other species and other times, they have nevertheless remained controversial both in psychology and in the biosocial sciences as a whole despite excellent selections of material for general and more sophisticated audiences - e.g. in the specialist works of Hans Eysenck (1979), Arthur Jensen (1980, 1981), Nat Brody (1992) and Charles Locurto (1991), and in the contributions to public debate by Herrnstein & Murray (1994), Itzkoff (1994), Rushton (1995) and Wooldridge (1994). Perhaps because there really are four broad questions that are all controversial, arguments about human differences in intelligence often take an unhelpful, question-hopping form. Discussions of IQ's degree of heritability can veer off into questions about whether there is 'any such one thing' as intelligence; and discussion of the fairness of tests can end in proclamations that what mental tests measure is anyhow unimportant. Herrnstein & Murray's The Bell Curve (1994) is an example of sustained and engaging presentation of new material about one of the questions about IQ - the fourth, psychotelic question; but it (quite deliberately) offered less coverage of the other three traditional questions. To that extent it did not help readers exercised by the full range of disputes about IQ and found itself criticized for ignoring other types of intelligence, for not saying what intelligence really was, and for vagueness about the role of heredity: instead of addressing the book's main psychotelic propositions, critics hopped to other questions that the authors had expressly set aside. The present book therefore tries to introduce all of the four questions and some of the main evidence relevant to each of them. While this approach risks superficiality, especially in a short introduction to intelligence, it is hoped to provide signposting to, and exemplifying detail of the main modern answers to all four questions. No bolt-hole will be left unflagged.
This book also makes a second assumption. It is not just that all four main questions about intelligence that need to be addressed within the same covers. The full range of arguments about intelligence is not always admitted by psychological writers. It can be attractive to concentrate on factual essentials and to encourage belief in a professional consensus among 'experts' - the works of Snyderman & Rothman (1989) and Seligman (1992/3) have this appeal. Yet drawing a veil over dissension with modern psychology may actually lose the confidence of readers. It probably needs to be admitted frankly that many educational, occupational, cognitive and developmental psychologists have remained edgy with, or sullenly hostile to the g factor - for all that few of them have at their command the daring or the scholarship of a Leon Kamin (1974, 1995). The lines of reply to them thus need to be sketched - though readers requiring detail will have to consult longer volumes. Thus the present short book tries to indicate the full range of issues that are at stake and the main lines of traditional and modern argument within psychology about each of them. In particular, relatively full coverage is given in turn to the specially controversial questions of:
- whether tests of the g type are fair to minorities;
- whether fundamental understanding of intelligence needs to be in terms of 'multiple components', 'cognitive strategies' and 'complex developmental interactions';
- whether accepting the existence of heritable g differences is to set out in the direction of 'fascism' or compulsory eugenics; and
- whether accepting the educational relevance of g would necessarily lead to a reimposition of educational streaming, segregation or any still wider apartheid.
The hope is that there is an advantage in facing up to these questions more directly than is usual in introductions to intelligence: research may thus be easier to consider dispassionately than when it is feared that its findings have implications that are both unadmitted unacceptable.
No-one can work seriously in the field of intelligence today without becoming involved in the controversies that arise as science begins to illuminate human nature and to challenge aspects of conservative, egalitarian, liberal or utopian ideologies. The problems are the more delicate in so far as today's familiar packages of social attitudes have themselves replaced packages of the past that were frankly tyrannical in tendency and grievously ill-informed. However, controversy yields comradeship too. So it is a pleasant duty for me to thank in particular friends, colleagues and students without whose help, encouragement and greatly valued criticism this book could hardly have been written: Dr Gail Addis, Professor Michael Anderson (University of Western Australia), Professor Tom Bouchard, Trish Connolly, Professor Ian Deary, Dr Vincent Egan, Professor Ray Fancher, Professor Peter Hacker, Professor Arthur Jensen, Dr Geoffrey Madell, Professor Nick Martin, George McMeekin, Zuleika von Meck, Magie Mieze, John Pate, Deirdre Quinn, Andrew Sadler, Dr Boris Semeonoff , Mary Stewart, Dr Con Stough, John Wakelin and Kate Ward. All who are familiar with these scholars and supporters of scholarship will know that they are emphatically not responsible for the book's mistakes.
EDINBURGH - January 1996