Richard Lynn - Sex Differences in Intelligence: The Developmental Theory

Arktos
London 2021

Copyright 2021 by Arktos Media Ltd.

All rights reserved. No part of this book may be reproduced or utilised in any form or by any means (whether electronic or mechanical), including photocopying, recording or by any information storage and retrieval system, without permission in writing from the publisher.

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ISBN

978-1-914208-65-2 (Softcover)

978-1-914208-66-9 (Hardback)

978-1-914208-67-6 (Ebook)

Editing

Constantin von Hoffmeister

Cover and Layout

Tor Westman

Chapter 1

A number of books and many thousands of papers have been published during the last century and a half on sex differences in intelligence as defined by Johnson, Carothers and Deary (2009) to mean the ability to use combinations of pre-existing knowledge and abstract reasoning to solve any of a variety of problems designed to assess the extent to which individuals can benefit from instruction or the amount of instruction that will be necessary to attain a given level of competence and measured as the IQ derived as the average of cognitive abilities obtained in tests like the Wechsler, the Stanford-Binet, the Cattell Culture Fair and numerous others. From the early twentieth century, virtually all authorities have contended that males and females have the same average intelligence. This book disputes this position and presents the developmental theory which states that in infants aged up to 4 years, girls have a higher average intelligence than boys, from the age of 6 to 15 there is little or no sex differences in intelligence, while from the age of 16 males begin to have higher average intelligence than females reaching an advantage of 4 to 5 IQ points in adults aged 21 and older.

In the nineteenth century, several authorities contended that men have a larger average brain size than women, that brain size is a determinant of intelligence and consequently that men have a higher average intelligence than women. This contention was advanced by Paul Broca (1861), the French physician and professor of medicine at the University of Paris, who is best known for his discovery that language is normally located toward the front of the brains left hemisphere, a region that is known as Brocas area. A decade later, the same contention was asserted by Charles Darwin, who wrote in The Descent of Man : The chief distinction in the intellectual powers of the two sexes is shown by man attaining to a higher eminence, in whatever he takes up, than woman can attainwhether requiring deep thought, or imagination, or merely the use of the senses and hands (Darwin, 1871). In the next decade, George Romanes, professor of medicine at the University of Oxford, took the same view: Seeing that the average brain weight of women is about five ounces less than that of men, on merely anatomical grounds we should expect a marked inferiority of intellectual power in the former In actual fact, we find the inferiority displays itself most conspicuously in a comparative absence of originality, and this more especially in the higher levels of intellectual work (Romanes, 1887).

With the invention of the intelligence test in the early twentieth century in France by Binet & Simon (1905a, 1905b), studies began to be published on sex differences in intelligence in which most authorities asserted that there is no difference between males and females. One of the first to advance this conclusion was Thorndike (1910, p. 35), who wrote of the trivial difference between the central tendency of men and women which is the common finding of psychological tests. This contention was also advanced in early studies in the United States by Terman (1916), who wrote that in the American standardisation sample of the Stanford-Binet test on 416 year-olds the superiority of girls over boys is so slight that for practical purposes it would seem negligible, and in England by Burt & Moore (1912).

In 1932, this contention was confirmed in the survey of the intelligence of all 11-year-olds in Scotland, in which boys (N=44,210) obtained a score of 34.506 and girls (N=43,288) obtained an almost identical score of 34.411 (Scottish Council, 1933). This study also found that the range of IQs was significantly greater in boys than in girls, given as IQ standard deviations of 14.9 for boys and 14.1 for girls by Deary (2020, p. 41). The effect of this is that 58.6 per cent with IQs below 60 were boys and 57.7 per cent with IQs above 130 were boys. Many later studies have confirmed that males have greater variance of intelligence than that of females, e.g., Lohman & Lakin (2009).

Many subsequent studies repeated the contention that males and females have equal intelligence. Thus Roberts (1945, p. 727): It is a striking fact that in mean performance on intelligence-test scales there should be no difference between boys and girls; Cattell (1971, p. 131): It is now demonstrated by countless and large samples that on the two main general cognitive abilitiesfluid and crystallized intelligencemen and women, boys and girls, show no significant differences; Hutt (1972, p. 88): There is little evidence that men and women differ in average intelligence; Maccoby & Jacklin (1974, p. 65): It is still a reliable generalisation that the sexes do not differ consistently in tests of total (or composite) abilities; Brody (1992, p. 323): Gender differences in general intelligence are small and virtually non-existent; Eysenck (1981, p. 40): Men and women average pretty much the same IQ; Herrnstein & Murray (1994, p. 275): The consistent story has been that men and women have nearly identical IQs; Jensen & Johnson (1994, p. 330): It remains a major unresolved puzzle in differential psychology and neuroscience that the large sex difference in head and brain size is not reflected by the mean IQ difference between males and females, which is virtually nil; Mackintosh (1996): There is no sex difference in general intelligence worth speaking of; Geary (1998, p. 310): The overall pattern suggests there are no sex differences, or only a small and unimportant advantage of boys and men, in average IQ scores.

The assertions that males and females have the same average IQ continued to be made in the twenty-first century. Thus: Lubinski (2000): Most investigators concur on the conclusion that the sexes manifest comparable means on general intelligence; Colom et al. (2000): We can conclude that there is no sex difference in general intelligence; Loehlin (2000, p. 177): There are no consistent and dependable male-female differences in general intelligence; Lippa (2002): There are no meaningful sex differences in general intelligence; Jorm et al. (2004): There are negligible differences in general intelligence; Bartholomew (2004, p. 91): Men on average have larger brains than women but display no significant advantage in cognitive performance; Anderson (2004, p. 829): The evidence that there is no sex difference in general ability is overwhelming; Haier, Jung, Head & Alkire (2004, p. 1): Comparisons of general intelligence assessed with standard measures like the WAIS show essentially no differences between men and women; Camarata & Woodcock (2006, p. 231): There appears to be general consensus for the view that males and females are not different in terms of general intellectual ability; Spelke & Grace (2007, p. 65): Men and women have equal cognitive capacity; Hines (2007, p. 103): There appears to be no sex difference in general intelligence; claims that men are more intelligent than women are not supported by existing data; Haier (2007): General intelligence does not differ between men and women; Halpern (2007, p. 123):There is no difference in intelligence between males and femalesoverall, the sexes are equally smart; Pinker (2008, p. 13): The two sexes are well matched in most areas, including intelligence; Mackintosh (2011, p. 380): The two sexes do not differ consistently in average IQ; Halpern (2012, p. 233): Females and males score identically on IQ tests; Lakin (2013, p. 263): Research indicates that men and women have equal or nearly equal ability in general intelligence; Dunst, Benedek, Koschutnig, Jauk & Neubauer (2014): There are no sex differences in general intelligence; Sternberg (2014, p. 178): There is no evidence, overall, of sex differences in levels of intelligence; Ritchie (2015, p. 105): Women tend to do better than men on verbal measures, and men tend to outperform women on tests of spatial ability; these small differences balance out so that the average general score is the same; Saini (2017, p. 85): When it comes to intelligence, it has been convincingly established that there are no differences between the average woman and man; Halpern & Kanaya (2017): There are no overall differences in female and male intelligence; Toivainen, Papageorgiou, Tosto & Kovas (2017, p. 81): Sex differences in general cognitive ability are overall small, if not negligible; Ackerman (2018, p. 8):There are negligible gender differences in omnibus IQ assessments; Warne (2020, p. 245): Males and females are equal in average intelligence; Halpern & Wai (2020, p. 335): Data showing differences between men and women in intelligence do not support the notion of a smarter sex; Deary, Cox & Hill (2021): There are very small or no sex differences in mean intelligence.