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Sex Differences in Intelligence

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Richard Lynn at Ulster University
Richard Lynn
Gerhard Meisenberg at Ross University, School of Medicine
Gerhard Meisenberg
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MANKIND QUARTERLY 2016 57:1 5-8
5
Editorial
Sex Differences in Intelligence
This special issue presents a number of papers challenging the widespread
consensus that there is no sex difference in general intelligence defined as the
IQ obtained from tests of a suite of reasoning, verbal, perceptual, memory and
spatial abilities like the Wechsler, Stanford-Binet and numerous others. This
position was asserted a century ago by Terman (1916) in reporting his
standardization of the Stanford-Binet in the United States in which he wrote “the
superiority of girls over boys is so slight … that for practical purposes it would
seem negligible.” This conclusion was frequently reasserted in the second half of
the twentieth century. Typical conclusions by leading authorities were those of
Cattell (1971, p. 131): “it is now demonstrated by countless and large samples
that on the two main general cognitive abilities – fluid and crystallized intelligence
– men and women, boys and girls, show no significant differences”; Brody (1992,
p. 323): “gender differences in general intelligence are small and virtually non-
existent”; and Jensen (1980, p. 360): “the sex difference in psychometric gis
either totally non-existent or is of uncertain direction and of inconsequential
magnitude.” Others who stated the same conclusion included Hutt (1972, p. 88),
Maccoby and Jacklin (1974, p. 65), Eysenck (1981, p. 40), and Herrnstein and
Murray (1994, p. 275).
This consensus was disputed by Lynn (1994), who advanced a
developmental theory of sex differences in intelligence stating that while there is
virtually no sex difference up to the age of 16 years, from this age onwards males
develop an advantage that increases with age reaching approximately 4 IQ points
among adults (Lynn, 1994). Further data documenting this male advantage was
given in Lynn (1999) and in a meta-analysis of sex differences on the Progressive
Matrices by Lynn and Irwing (2004) concluding that among adults males obtain a
5 points higher IQ than females.
The most frequent reaction to Lynn's theory has been to ignore it and
continue to assert that there is no sex difference in intelligence. For instance:
“Women’s brains are 10% smaller than men’s, but their IQ is on average the
same” (Butterworth, 1999, p. 293); “It is an important finding of intelligence testing
that there is no difference between the sexes in average intellectual ability; this is
true whether general ability is defined as an IQ score calculated from an omnibus
test of intellectual abilities such as the various Wechsler tests, or whether it is
MANKIND QUARTERLY 2016 57:1
6
defined as a score on a single test of general intelligence, such as Raven’s
Matrices... the evidence that there is no sex difference in general ability is
overwhelming” (Anderson, 2004, p. 829); “Men and women have equal cognitive
capacity” (Speke, 2007, p. 65); “There appears to be no sex difference in general
intelligence; claims that men are more intelligent than women are not supported
by experimental data” (Hines, 2007, p. 103); “General intelligence does not differ
between men and women” (Haier, 2007); “There is no difference in intelligence
between males and females…overall, the sexes are equally smart” (Halpern,
2007, p. 123); “The two sexes do not differ consistently in average IQ”
(Mackintosh, 2011, p. 380); “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”
(Ritchie, 2015, p. 105); “In adulthood, there is scant evidence for sex differences
in g, although women tend to perform better than men in verbal tasks, whilst men
outperform women slightly in spatial tasks” (Cooper, 2015, p. 207).
These quotations illustrate that there are two questions that need to be
examined. One is the possibility that there is a sex difference in the general ability
factor g, which is technically defined as the unrotated first factor or principal
component of a factor analysis or principal components analysis and is very close
to the IQ calculated from a battery of diverse tests. The other is the possibility that
there are sex differences on specialized abilities rather than on g, such that
women excel in some abilities and men in others. The likely presence of both
kinds of difference adds complexity to the question, and explains the often
inconsistent results that studies of sex differences at the latent factor level have
produced in the past (e.g., Keith et al., 2008; Lemos et al., 2013).
The ongoing debate about sex differences is based almost exclusively on
results from modern Western societies. It does not take account of the possibility
that there could be systematic differences between countries with different school
systems, cultural traditions, and gender roles. Thus there is an urgent need to
expand the evidence base on which theories about sex differences are built by
including results from a greater variety of countries.
Filling this gap is the aim of this special issue of Mankind Quarterly, which
presents new results about sex differences in Brazil, Chile, the United States,
Sweden, Russia, Korea, Taiwan, Thailand, Egypt, Libya, Sudan and Yemen.
Most results show sex differences in “general” ability to be small, and most show
marginal to solid male advantages. Those who expect large and systematic
differences between countries in the size, direction or pattern of sex differences
may be disappointed. The results indicate that such differences between
EDITORIAL
7
countries and world regions, if present, are not of large magnitude and may be
difficult to demonstrate in more systematic surveys of the literature.
However, this “null” result is itself interesting because it suggests that cultural
and in particular educational and ideological forces have limited ability in shaping
sex differences in the levels and patterns of ability and achievement. For
example, if it is considered desirable to masculinize female ability and
achievement patterns by raising women’s mechanical comprehension and
reducing their psychomotor speed and social skills to male levels, education and
indoctrination may not be sufficient. Something else may be required. One option
would be prenatal testosterone treatment for female fetuses. Clinical studies
suggest that this may actually work (Hampson, Rovet & Altmann, 1998; Hier &
Crowley, 1982).
References
Anderson, M. (2004). Sex differences in general intelligence. In: R.L. Gregory (ed.), The
Oxford Companion to the Mind. Oxford: Oxford University Press.
Brody, N. (1992). Intelligence. San Diego, CA: Academic Press.
Butterworth, B. (1999). The Mathematical Brain. London: Macmillan.
Cattell, R.B. (1971). Abilities: Their Structure, Growth and Action. Boston: Houghton
Mifflin.
Cooper, C. (2015). Intelligence and Human Abilities. London: Routledge.
Eysenck, H.J. (1981). In H.J. Eysenck and L. Kamin: Intelligence: The Battle for the Mind:
H.J. Eysenck versus Leon Kamin, pp. 11-89. London: Pan.
Haier, R. (2007). Brains, bias, and biology: Follow the data. In: S.J. Ceci & W.M. Williams
(eds.), Why Aren’t There More Women in Science? Washington, D.C.: American
Psychological Association.
Halpern, D. (2007). Science, sex and good sense: Why women are underrepresented in
some areas of science and math. In S.J.Ceci & W.M.Williams (eds.), Why Aren’t There
More Women in Science? Washington, D.C.: American Psychological Association.
Hampson, E., Rovet, J.F. & Altmann, D. (1998). Spatial reasoning in children with
congenital adrenal hyperplasia due to 21-hydroxylase deficiency. Developmental
Neuropsychology 14: 299-320.
Herrnstein, R. & Murray, C. (1994). The Bell Curve. New York: Random House.
MANKIND QUARTERLY 2016 57:1
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Hier, D.B. & Crowley, W.F. (1982). Spatial ability in androgen-deficient men. New England
Journal of Medicine 306: 1202-1205.
Hines, M. (2007). Do sex differences in cognition cause the shortage of women in
science? In: S.J. Ceci & W.M. Williams (eds.), Why Aren’t There More Women in
Science? Washington, D.C.: American Psychological Association.
Hutt, C. (1972). Males and Females. Harmondsworth, UK: Penguin Books.
Jensen, A.R. (1980). Bias in Mental Testing. London: Methuen.
Keith, T.Z., Reynolds, M.R., Patel, P.G. & Ridley, K.P. (2008). Sex differences in latent
cognitive abilities ages 6 to 59: Evidence from the Woodcock-Johnson III tests of cognitive
abilities. Intelligence 36: 502-525.
Lemos, G.C., Abad, F.J., Almeida, L.S. & Colom, R. (2013). Sex differences on gand
non-gintellectual performance reveal potential sources of STEM discrepancies.
Intelligence 41: 11-18.
Lynn, R. (1994). Sex differences in brain size and intelligence: A paradox resolved.
Personality and Individual Differences 17: 257-271.
Lynn, R. (1999). Sex differences in intelligence and brain size: A developmental theory.
Intelligence 27: 1-12.
Lynn, R. & Irwing, P. (2004). Sex differences on the Progressive Matrices: A meta-
analysis. Intelligence 32: 481-498.
Maccoby, E.E. & Jacklin, C.N. (1974). The Psychology of Sex Differences. Stanford, CA:
Stanford University Press.
Mackintosh, N.J. (2011). IQ and Human Intelligence, 2nd edition. Oxford: University Press.
Ritchie, S. (2015). Intelligence. London: John Murray Learning.
Speke, E. (2007). Sex, math and science. In: S.J. Ceci & W.M. Williams (eds): Why Aren’t
There More Women in Science? Washington, D.C.: American Psychological Association.
Terman, L.M. (1916). The Measurement of Intelligence. Boston, MA: Houghton Mifflin.
Richard Lynn
Gerhard Meisenberg
... This lack of a major sex difference in negative creativity -which has now been found with samples from two countries -is puzzling. Moreover, intelligence is an important component of creativity (Eysenck, 1993), and while some researchers aver that adult males have the same IQ as adult females (Flynn, 2012) others argue that there is some evidence that adult males possess an IQ advantage of approximately 4 points (Lynn, 2021). Certainly, males are over-represented at the IQ-extremes; there is more male variability (Lynn, 2021). ...
... Moreover, intelligence is an important component of creativity (Eysenck, 1993), and while some researchers aver that adult males have the same IQ as adult females (Flynn, 2012) others argue that there is some evidence that adult males possess an IQ advantage of approximately 4 points (Lynn, 2021). Certainly, males are over-represented at the IQ-extremes; there is more male variability (Lynn, 2021). Secondly, the MCBS scale may have low content validity with regard to the construct of malevolent creativity, as well as to creativity more generally. ...
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Malevolent creativity refers to employing creative processes for one's own selfish gain, often combined with detrimental effects on others. Sex differences in malevolent or negative creativity are to be expected due to the established finding that males are higher in the Dark Triad traits. However, the only previous study of this issue, using a sample of Indian students, did not find a sex difference. Here, we administered the Malevolent Creativity Behaviour Scale (MCBS) to a sample of 1619 Sudanese students, and found a small sex difference in that females rated themselves higher. Reasons for the finding are explored, including possible problems with the MCBS instrument.
Is Success or Failure at Solving Complex Problems Related to Intellectual Ability?
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  • Jun 2003
INTRODUCTION Imagine you are elected mayor of a town and are given absolute power over all town resources. You may hire workers for the local factory, raise taxes, have schools built, and close down local businesses. The one goal you are to strive for is to make certain that the town prospers. A situation like this, simulated on a computer, was used in the early 1980s by Dietrich Dörner and his colleagues (e.g., Dörner & Kreuzig, 1983; Dörner, Kreuzig, Reither, & Stäudel, 1983) in Bamberg, Germany, to study individual differences in the human ability to solve complex problems. Dörner was interested in understanding why some of his research participants were much more successful in building prosperous towns than were others. One of his rather striking and hotly debated conclusions was that individual differences in the ability to govern the simulated town were not at all related to the individuals' IQs. Rather, an individual's ability to turn the town into a prosperous community seemed to be related to his or her extroversion and self-confidence. In this chapter we are concerned with the question of what determines individual differences in complex problem-solving competence. The answer to this question may be traced from many different viewpoints: cognitive, social, biological, and evolutionary, to name just a few. Here, we focus on the contribution of cognitive psychology to providing an answer to the question.
Testing the developmental theory of sex differences in intelligence on 12–18 year olds
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Full-text available
The consensus view states that there are no sex differences in intelligence. However, Lynn (1994, 1999) has formulated a developmental theory of sex differences in intelligence that challenges that view. The theory states that boys and girls mature at different rates such that the growth of girls accelerates at the age of about 9 years and remains in advance of boys until 14–15 years. At 15–16 years the growth of girls decelerates relative to boys. As boys continue to grow from this age their height and their mean IQs increase relative to those of girls. This paper presents new evidence for the theory from the Spanish standardization sample of the fifth edition of the DAT. 1027 boys and 924 girls between 12 and 18 years were tested. The general trend shows that girls do better at the younger ages and their performance declines relative to boys among older age groups, which supports the developmental theory. The sex difference for the DAT as a whole for 18 year olds is a 4.3 IQ advantage for boys, very close to the advantage that can be predicted from their larger brain size (4.4 IQ points). The profile of sex differences in abilities among the Spanish sample is closely similar to that in the United States and Britain, which is testimony to the robustness of the difference in these different cultures.
Sex differences on the progressive matrices among adolescents: Some data from Estonia
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It has long been asserted that there are no sex differences on the Progressive Matrices. Contrary to this position, it has been contended by Lynn (1994, 1998) that there is a small difference favoring females from the age of approximately 9–14 years, and a difference favouring males from the age of 16 onwards, reaching approximately 2.4 IQ points among adults. Data to test these two theories are reported from a standardization of the Progressive Matrices on a sample of 2689 12–18 year olds in Estonia. The results confirm the Lynn theory and show a female advantage of 3.8 IQ points among 12–15 year olds and a male advantage of 1.6 IQ points among 16–18 year olds. Boys had a significantly larger standard deviation than girls. The results provide further confirmation that in early adolescence girls outperform boys on abstract (non-verbal) reasoning ability but that in later adolescence boys outperform girls.
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This review paper examines two related areas of research: studies dating back over 50 years on lay theories of the nature and measurement of intelligence, and more recent research on sex and culture differences on self-estimated intelligence. The latter focus is on the nearly 20 published papers on estimated intelligence. Studies have shown consistent sex differences with males rating themselves higher than females. There are also consistent generational effects with adult participants believing around a half standard deviation difference in intelligence with their grandparents being least intelligent and children most. Self-estimated and psychometric intelligence only correlates weakly. Studies looking at self and other estimates of multiple intelligence indicated that participants seemed to believe that intelligence was male normative in that it was specifically those types of intelligence (mathematical and spatial) that most differentiated between the sexes that were themselves more predictive of general overall intelligence. Implications of these findings for intelligence testing are considered.
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Sex differential item functioning in the Raven's Advanced Progressive Matrices: Evidence for bias
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Spatial reasoning in children with congenital adrenal hyperplasia due to 21‐hydroxylase deficiency
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Full-text available
  • Jan 1998
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Full-text available
In 1992, it was reported by Ankney and Rushton that males have larger average brain size than females even when allowance is made for body size. It is known that brain size is associated with intelligence, and it would therefore be expected that males would have higher intelligence than females. Yet it has been universally maintained that there is no difference in intelligence between the sexes. It is proposed that this anomaly can be resolved by a developmental theory of sex differences in intelligence which states that girls mature more rapidly in brain size and neurological development than boys up to the age of 15 years. The faster maturation of girls up to this age compensates for their smaller brain size with the result that sex differences in intelligence are very small, except for some of the spatial abilities. From the age of 16 years onwards, the growth rate of girls decelerates relative to that of boys. The effect of this is that a discernible male advantage of about 4 IQ points develops from the age of 16 into adulthood, consistent with the larger average male brain size. This paper presents new evidence on the developmental theory of sex differences in intelligence and discusses alternative attempts to deal with the anomaly by Ankney (1995), Mackintosh (1996), and Jensen (1998).
The Psychology of Sex Differences
Book
  • Jan 1974
Sex differences in general intelligence: A reappraisal
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  • Jan 2005
The Bell Curve
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Bias in Mental Testing
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  • Jul 1980
Sex differences on g and non-g intellectual performance reveal potential sources of STEM discrepancies
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The analysis of sex differences in cognitive abilities is largely confusing because these differences are masked by the pervasive influence of the general factor of intelligence (g). In this study a battery of five reasoning tests (abstract [AR], numerical [NR], verbal [VR], mechanical [MR], and spatial [SR]) was completed by a sample of 3233 young and old adolescents representative of the population. Using a latent variable approach, mean differences on the general factor were estimated after examining measurement invariance. Results show that the difference, favoring boys in latent g increases with age from two to four IQ points. Further, boys outperform girls in all the subtests and the observed differences were generally explained by g. However, mechanical reasoning is a systematic and strong exception to this finding. For the young adolescents, the observed difference in MR is equivalent to 10 IQ points, and this difference increases to 13 IQ points for the old adolescents. Only 1 (young) or 2 (old) IQ points of the sex difference in MR can be accounted for by g. The findings suggest that the persistent – and usually neglected average large advantage of boys in mechanical reasoning (MR) — orthogonal to g – might be behind their higher presence in STEM (science, technology, engineering, and math) disciplines. A new look at this relevant social issue is proposed in this study.
Do Sex Differences in Cognition Cause the Shortage of Women in Science?
Article
I have spent much of my research career (about 30 years now) studying the influences of sex hormones, particularly androgens, such as testosterone, and estrogens, such as estradiol, on behavior. I am trained as a clinical psychologist and as a personality and developmental psychologist, as well as a neuroendocrinologist and neuroscientist, and I bring all of these perspectives to my work. Much of my research has investigated cognitive outcomes in individuals with genetic abnormalities causing sex-atypical hormone exposure prenatally or has evaluated the consequences of hormone treatment, either prenatally or in adulthood, on human cognition. On the basis of my 30 years of work, I believe the short answer to the question posed in the title of this chapter is "no." Innate sex differences in cognitive abilities do not cause the shortage of women in science. A somewhat longer answer follows. It draws heavily on my book, Brain Gender (Hines, 2004), and interested readers are referred there for a more detailed discussion of the points made here. Topics covered in this chapter include cognitive sex differences, gonadal hormones prenatally and human cognition (organizational influences), and gonadal hormones in adulthood and human cognition (activational influences). (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Abilities: Their Structure, Growth, and Action
Article
The Measurement of Intelligence
Article
  • Jan 1916
Adapted from The measurement of intelligence Houghton, Mifflin and Co. (see record 2004-16193-000) by L. M. Terman. Terman's revision and extension of Binet and Simon's tests, known as the Stanford-Binet, was the first to have adequate standardization through the school years, and quickly became the most widely used individual intelligence test. Although the Binet scale quickly demonstrated its value as an instrument for the classification of mentally-retarded and otherwise exceptional children, it had, nevertheless, several imperfections which greatly limited its usefulness. There was a dearth of tests at the higher mental levels, the procedure was so inadequately defined that needless disagreement came about in the interpretation of data, and so many of the tests were misplaced as to make the results of an examination more or less misleading, particularly in the case of very young subjects and those near the adult level. It was for the purpose of correcting these and certain other faults that the Stanford investigation was planned. This chapter examines: sources of data; method of arriving at a revision; a brief summary of the results of the investigation of 1,000 intelligence quotients; validity of the IQ; sex differences; intelligence of the different social classes; relation of IQ to the quality of the child's school work; relation between IQ and school progress; and correlation between IQ; and the teacher's estimates of the child's intelligence. (PsycINFO Database Record (c) 2012 APA, all rights reserved)