Sex differences are in the news. A male Google employee reviewed some of the literature on the topic in the context of his workplace practices, and got sacked. A book questioning the role of testosterone in sex differences, and more generally the veracity of innate biological sex differences, got the Royal Society Science Book prize, though it was not reviewed by Royal Society Fellows expert in that area of knowledge. More generally, there are frequent news items about the lack of women in STEM subjects, in technology jobs and in corporate boardrooms, and these discussions often blame a glass ceiling of misogyny impeding women’s progress. Meanwhile, with rather less publicity, Prof Richard Lynn has revisited his 1994 paper in the light of recent research, and invited critics to take his finding apart.
As Editor Gerhard Meisenberg comments:
In this issue of Mankind Quarterly, Richard Lynn presents a data-rich summary of his developmental theory, followed by 10 comments by scholars working in the field and a reply to the comments. Many of the commentators add pieces of empirical evidence to the puzzle of sex differences, while others propose theoretical alternatives or refinements to the developmental theory. Taken together, the target article and comments offer a fairly representative overview of the current status of research on cognitive sex differences and the theoretical approaches used by different researchers in the field.
Here are the papers:
Sex Differences in Intelligence: The Developmental Theory. Richard Lynn
Male and Female Balance Sheet. James R. Flynn
Counting is not Measuring: Comment on Richard Lynn’s Developmental Theory of Sex Differences in Intelligence. Roberto Colom
Common Paradoxes in the Study of Sex Differences in Intelligence. Helmuth Nyborg
Cognitive Sex Differences: Evolution and History. David Becker and Heiner Rindermann
The Male Brain, Testosterone and Sex Differences in Professional Achievement. Edward Dutton
Sex Differences in Intelligence: Developmental Origin Yes, Jensen Effect No. Gerhard Meisenberg
Sex Differences in Self-Estimated Intelligence, Competitiveness and Risk-Taking. Adrian Furnham
Sex Differences in Intelligence: A Genetics Perspective. Davide Piffer
Presumption and Prejudice: Quotas May Solve Some Problems,but Create Many More.
Sex Differences in Cognitively Demanding Games: Poker, Backgammon and Mahjong.
Heitor B.F. Fernandes
Sex Differences in the Performance of Professional Go Players. Mingrui Wang
Sex Differences in Intelligence: Reply to Comments. Richard Lynn
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Prof Lynn begins with the following observation:
It is a paradox that males have a larger average brain size than females, that brain size is positively associated with intelligence, and yet numerous experts have asserted that there is no sex difference in intelligence. This paper presents the developmental theory of sex differences in intelligence as a solution to this problem. This states that boys and girls have about the same IQ up to the age of 15 years but from the age of 16 the average IQ of males becomes higher than that of females with an advantage increasing to approximately 4 IQ points in adulthood.
Lynn goes on to show that most experts in the field assert that there are no sex differences in intelligence, or that such differences that exist cancel each other out. He then goes on to consider the obvious anomaly, that since brain size is related to intelligence, and men have larger brains than women, they ought to be more intelligent.
Pakkenberg and Gundersen (1997) reported that men have an average of four billion more neurons than women, a difference of 16 percent. Further data showing that men have more neurons than women, have been given by Pelvig et al. (2008).
Lynn then explains how he made his prediction about higher male intelligence:
To calculate the magnitude of the higher adult male IQ that would be predicted from the larger male brain size I took Ankney’s figure of the male-female difference in brain size expressed in standard deviation units of 0.78d and Willerman et al.’s (1991) estimate of the correlation between brain size and intelligence of 0.35. These figures would give adult males a higher average IQ of 0.78 multiplied by 0.35 = .27d = 4.0 IQ points. In my 1994 paper I presented data showing adult male advantages of 1.7 IQ points on verbal ability, 2.1 IQ points on verbal and non-verbal reasoning ability, and 7.5 IQ points on spatial, giving an average male advantage among adults of 3.8 IQ points and thus very close to the predicted advantage of 4.0 IQ points. I published further data for this male advantage in Lynn (1998, 1999). The male advantages given by Meisenberg (2009) given in Table 1 of 0.42d for whites and 0.30d for blacks are reasonably consistent with these results.
Eysenck accepted my thesis that men have a 4 points higher IQ than women and calculated that this advantage combined with the greater male variance of a standard deviation of 15 for men and 14 for women would produce 55 men and 5 women per 10,000 with an IQ of 160 and above, a ratio of 10:1. The same point has been made more recently by Nyborg (2015, p. 51), who presents data for a male advantage of 3.9 IQ points among American white 17 year olds and calculates that this advantage gives men a ratio of 5:1 to women at an IQ of 145 (approximately one per 300 males).
You may remember that I played around with these figures showing the male/female ratios which resulted from different assumptions about male/female differences in intelligence, and male/female differences in standard deviations.
Back to Lynn.
Table 1 shows how, as male brains become bigger their intelligence advantage grows bigger.
In fact, even on the children’s version of the Wechsler (ages 6 to 16) there is a male advantage, and clear sex differences in the four indexes of ability, girls showing a processing speed advantage. As Lynn wryly observes, everyone has been wrong that there are no sex differences on the Wechsler which is a broad test of abilities, administered face to face and thus able to monitor engagement and effort. Furthermore, he has been wrong that sex differences do not show up till 16. They are present before that.
On the adult Wechsler, over 33 studies show that there is a clear pattern of male advantage, equivalent to 3.8 IQ points.
The more detailed nature of adult sex differences in ability are shown in Table 6
Note that these differences are present even in the standardization samples of the test (shown with an asterisk), a finding the publishers are reluctant to publicize, and which Lynn only obtained by being the first to ask them for the data. That means that the Wechsler has found a sex difference but then standardized it away, so that when a clinician looks up results in the manual tables, an inherent sex difference is hidden. Something of a scandal, to my mind.
In fact, for a long time test constructors have worked to minimize male advantage, omitting tasks on which they had better scores, such as spatial perception and mental rotation of shapes, and mechanical knowledge (10 IQ difference for the latter).
The median male advantage of 3.6 IQ points on the WAIS Full Scale IQ in all 33 samples is a disconfirmation of the assertions by Halpern (2000, p. 91), Anderson (2004, p. 829) and Haier et al. (2004, p.1) that there is no sex difference on the WAIS Full Scale IQ. It is also a disconfirmation of Halpern’s (2012, p. 115) assertion that in the standardization sample of the American WAIS IV “the overall IQ score does not show sex differences”.
Turning to sex differences in high achievement, Lynn notes:
Howard reported that in 2012 there were 1324 men and 26 women Chess grandmasters and over the years 1975 to 2014 there was a male advantage of about one standard deviation in the performance of the top 10 and top 50 of all international players. He concluded that higher male ability is the most plausible explanation for the greater number of men among top Chess players: “Males score higher on average in visuospatial abilities and many more males score at the upper IQ extreme” and that the male predominance in Chess is “probably partly innate” (p. 219-20). He was right that the much greater number of men with high IQs is part of the explanation for their much greater number of among top Chess players.
There is much more in this paper, which you can read for yourselves, but my feeling is that Lynn has made a strong case for a male advantage in intelligence, and critics must now engage him on the detailed results he presents.
Have they done so? That is enough for now. Later I will talk about the replies to his paper contained in the special issue, and also draw attention to the non-replies, on the Sherlock Holmes principle that the dogs that do not bark are also worthy of attention.
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