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BOOK RFVIEWS 165

depth is, alas, another matter. They say that only eight thousand of the twenty thousand questionnaires which were sent out were returned completed. A rough count suggests that British psychologists are in general no better represented than those of other countries, since there are about 750 entries for the United Kingdom.

Despite its shortcomings, which are in no way the responsibility of the editors, this Directory is a most valuable one; it does not, of course, include American psychologists, because the Directory of the American Psychological Association is readily available. c. B. FRISBY

Genetic and Environmental Factors in Human Ability. Edited by J. E. MEADE and A. s. PARKF.S. London; Oliver and Boyd, 1966. Pp. xi + 242. Price 57s. 6d.

This volume contains a report of the proceedings of the second of the series of symposia held by the Eugenics Society, with the object of bringing together experts from tbe various fields of genetics, physiology, psychology, and other branches of the social sciences to promote an exchange of ideas. The general theme of this symposium, held in October 1965, was a need for fresh thinking about some of the more vital aspects of the educational system. There are four main parts, entitled respectively 'The Nature and Meaning of Intelligence Tests', 'Selection for Higher Education', 'Aspects of Subnormality' and 'Differential Fertility and Intelligence".

The contributions are necessarily short and of varying quality. Few have anything new to say, except papers in the last section, and some are anecdotal rather than scientific. There are some interesting contradictions; thus geneticists seem to be more firmly convinced of the heritability of individual differences in intelligence than are the psychologists (except Professor Wiseman, who presents much new and interesting material). The geneticists probably have the better of it; some of the psychological contributions are not as clear and unambiguous as they might be. Even P. E. Vernon in his chapter comes perilously close to self- contradiction in his attempt to devalue the genetic approach. Thus he says 'identical twins tend to be brought up much more alike than ordinary siblings or fraternal twins and thus would be expected to show higher correlations'. He then comments on the evidence from identical twins brought up apart which he considers impossible to interpret 'since the members of separate pairs are unlikely to be placed in different environments at random'. But the most comprehensive study by Shields, not quoted by Vernon, shows that identical twins brought up in different environments are very slightly more alike in intelligence test scores than are identical twins brought up together in the same family. Here then is the contradiction: Vernon has to assume that the rather slight differences in environmental treatment meted out to identical and fraternal twins respectively fhis 'much more alike' is surely an exaggeration, and not supported by any research I am familiar with) produce tremendous differences in the intra-class correlations, whereas the surely much greater differences, as meted out to identical twins brought up in different families produce no difference in intra-class correlations whatsoever. Thus environment, rather like the aether of the pre-Einstein physicists, is endowed with contradictory qualities.

In a similar way Himmelweit seems to beg the question when ;5he points out that correlations between social class, school performance, and early leaving tend to be_ in the region of 0,25; 'these results certainly show that many thousands of children do not realise their intellectual potential and that this constitutes a serious social problem requiring remedial action'. There seems to be an 'un-

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distributed middle' somewhere; certainly the argument only makes sense if we discount the influence of heredity completely.

The book is worth its price for the well-written and informative biological papers, particularly perhaps those dealing with differential fertility which contain some interesting new applications of statistical methods to social and psychological problems. There are of course many other points of interest too, although their relevance to the main theme of the relevance to educational systems is not always evident. Probably none of the participants would quarrel with Lord Robbins's final conclusion 'that we need more university places than have been promised hitherto', and that mental tests, whatever the contribution of heredity and environment, cannot provide an alternative. H. J. EYSENCK

Mental Deficiency: The Changing Outlook. Edited by ANN M. cr,ARKE and A. D. B. CLARKE. Second Edition. London: Methuen, 1966. Pp. xxi + 596. Price 63 s.

This is the second, revised edition, of the book originally published seven years earlier; the first edition immediately achieved considerable success, and the second edition will undoubtedly become equally widely accepted. The eighteen chapters which make up the three parts (background; theoretical problems; practical problems) are written by different authors but extremely well integrated. There is a valuable list of some 1,200 references, although this list is somewhat inflated by the inclusion of quite useless and irrelevant material; thus Gunzburg, on page 310. gives a long series of references to tests which, as he himself points out, have not been widely used in mental deficiency work! The reason for the inclusion, apparently, is that these might in time produce valuable material, a hopeful prognostication which the reviewer does not share, particularly as the tests in question have been singularly barren even when they have been put to use in other contexts.

It is impossible to review in detail a book so packed with factual information and dealing with so wide a range of problems. Inevitably small errors and dubious statements occur. Thus it is said on page 96 that 'there is reason to believe that environment, both pre- and post-natal, of identical twins is more similar for each pair than for fraternals'. No reference is given but the evidence suggests that the prenatal environment of identical twins is in fact less similar than that of fraternals. Neither is it true, as stated on the same page, that 'differentiation of identical from fraternal twins is not perhaps as straightforward as it might seem'. A very high degree of accuracy can in fact be achieved with relative ease, and even simple questionnaire methods have been found surprisingly accurate when checked against more sophisticated blood type and finger print tests. In any case. as should perhaps have been pointed out. any errors in diagnosis lower the estimation of heritability below the true value.

In spite of minor infelicities of this kind, the book preserves an admirable level of factual accuracy, theoretical sophistication and unbiased assessment of complex and difficult issues. Editors and authors are to be congratulated on not only having wrought a revolution in our general attitude towards mental deficiency, but also for having painted so clear a picture of the present position. H. J. EYSENCK